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  • 251.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Rocchio-Heller, Riston
    Oerlikon Metco, Westbury, USA.
    Liu, Jing
    Oerlikon Metco, Westbury, USA.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery, Fingspång, Sweden.
    Östergren, Lars
    GKN Aerospace, Trollhättan, Sweden.
    Multilayered suspension plasma sprayed thermal barrier coatings for high temperature gas turbine applications2017In: Proceedings of the International Thermal Spray Conference & Exposition (ITSC 2017), New York: Curran Associates, Inc , 2017, p. 382-387Conference paper (Refereed)
    Abstract [en]

    Improvement in the performance of thermal barrier coating systems (TBCs) is one of the key objectives for further development of gas turbine applications. The material most commonly used as TBC topcoat is yttria stabilised zirconia (YSZ). However, the usage of YSZ is limited by the operating temperature range which in turn restricts the engine efficiency. Materials such as pyrochlores, perovskites, rare earth garnets, etc. are suitable candidates which could replace YSZ as they exhibit lower thermal conductivity and higher phase stability at elevated temperatures.The objective of this work was to investigate different multi-layered TBCs consisting of advanced topcoat materials fabricated by Suspension Plasma Spraying (SPS). The investigated topcoat materials were YSZ, dysprosia stabilised zirconia, gadolinium zirconiate, cerium doped YSZ and yttria fully stabilised zirconia. All topcoats were deposited with TriplexPro-210 plasma spray gun and radial injection of suspension. Lifetime of these samples was examined by thermal cyclic fatigue and thermal shock testing. Microstructure analysis of as-sprayed and failed specimens was performed with scanning electron microscope. The failure mechanisms in each case have been discussed in this article. The results show that SPS could be a promising route to produce multilayered TBCs for high temperature applications.

  • 252.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    A modelling approach to design of microstructures in thermal barrier coatings2013In: Journal of Ceramic Science and Technology, ISSN 2190-9385, Vol. 4, no 2, p. 85-92Article in journal (Refereed)
    Abstract [en]

    Thermo-mechanical properties of TBCs are strongly influenced by coating defects, such as delaminations and pores, thus making it essential to have a fundamental understanding of microstructure-property relationships in TBCs to produce a desired coating. Object-Oriented Finite element analysis (OOF) has been shown previously as an effective tool for evaluating thermal and mechanical material behaviour, as this method is capable of incorporating the inherent material microstructure as an input to the model. In this work, OOF was used to predict the thermal conductivity and effective Young's modulus of TBC topcoats. A Design of Experiments (DoE) was conducted by varying selected spray parameters for spraying Yttria Stabilized Zirconia (YSZ) topcoat. Microstructure was assessed with SEM and image analysis was used to characterize porosity content. The relationships between microstructural features and properties predicted by modelling are discussed. The microstructural features having the most beneficial effect on properties were sprayed with another spray gun so as to verify the results obtained from modelling. Characterisation of the coatings included microstructure evaluation, thermal conductivity and lifetime measurements. The modelling approach in combination with experiments undertaken in this study was shown to be an effective way in achieving coatings with optimised thermo-mechanical properties.

  • 253.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nylén, Per
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Structure-property Relationships in Thermal Barrier Coatings by Finite Element Modelling2012In: Surface Modification Technologies XXV : proceedings of the Twenty Fifth International Conference on Surface Modification Technologies: SMT25, Trollhättan, June 20-22, 2011 / [ed] T. S. Sudarshan, and P. Nylén, [Chennai]: Valardocs , 2012, p. 175-184Conference paper (Refereed)
    Abstract [en]

    The thermal and mechanical properties of Thermal Barrier Coating systems (TBCs) are strongly influenced by coating defects, such as delaminations and pores, thus making it essential to have a fundamental understanding of microstructure-property relationships in TBCs, to produce a desired coating. Object-Oriented Finite element analysis (OOF) has been shown previously as an effective tool for evaluating thermal and mechanical material behaviour, as this method is capable of incorporating the inherent material microstructure as an input to the model. In this work, OOF was used to predict the thermal conductivity and effective Young’s modulus of TBC topcoats. A Design of Experiments (DoE) was conducted by varying selected spray parameters for spraying Yttria Partially Stabilized Zirconia (YPSZ) topcoat. Characterisation of the coatings included microstructure, porosity and crack content and thermal conductivity measurements. The relationships between microstructural features, thermal conductivity and Young’s modulus are discussed.

  • 254.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Skogsberg, Kristoffer
    University West, Department of Engineering Science.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Influence of topcoat-bondcoat interface roughness on stresses and lifetime in Thermal Barrier Coatings2013In: Proceedings of the International Thermal Spray Conference / [ed] Editor: Rogerio S. Lima, Arvind Agarwal, Margaret M. Hyland, Yuk-Chiu Lau, Georg Mauer, André McDonald, and Filofteia-Laura, ASM International, 2013, p. 596-601Conference paper (Refereed)
    Abstract [en]

    Failure in Atmospheric Plasma Sprayed (APS) Thermal Barrier Coatings (TBCs) is associated with the thermomechanical stresses developing due to the Thermally Grown Oxide (TGO) layer growth and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs. Modeling has been shown as an effective tool to understand the effect of interface roughness on induced stresses. In previous work done by the research group, it was observed that APS bondcoats performed better than the bondcoats sprayed with High Velocity OxyFuel (HVOF) process which is contrary to the present literature data. The objective of this work was to understand this observed difference in life-time with the help of finite element modeling by using real surface topographies. Different TGO layer thicknesses were evaluated. The modeling results were also compared with existing theories established on simplified sinusoidal profiles published in earlier works. It was shown that modeling can be used as an effective tool to understand the stress behavior in TBCs with different roughness profiles.

  • 255.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Skogsberg, Kristoffer
    University West, Department of Engineering Science.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Influence of Topcoat-Bondcoat Interface Roughness on Stresses and Lifetime inThermal Barrier Coatings2014In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 23, no 1-2, p. 170-181Article in journal (Refereed)
    Abstract [en]

    Failure in Atmospheric Plasma Sprayed (APS) Thermal Barrier Coatings (TBCs) is associated with the thermo-mechanical stresses developing due to the Thermally Grown Oxide (TGO) layer growth and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs. Modeling has been shown as an effective tool to understand the effect of interface roughness on induced stresses. In previous work done by our research group, it was observed that APS bondcoats performed better than the bondcoats sprayed with High Velocity Oxy-Fuel (HVOF) process which is contrary to the present literature data. The objective of this work was to understand this observed difference in lifetime with the help of finite element modeling by using real surface topographies. Different TGO layer thicknesses were evaluated. The modeling results were also compared with existing theories established on simplified sinusoidal profiles published in earlier works. It was shown that modeling can be used as an effective tool to understand the stress behavior in TBCs with different roughness profiles.

  • 256.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Weber, A.
    Karlsruhe Institute of Technology, Karlsruhe, Germany .
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Gindrat, M.
    Oerlikon Metco, Wohlen, Switzerland.
    Electrochemical performance of plasma sprayed metal supported planar solid oxide fuel cells2015In: ECS Transactions, ISSN 1938-5862, E-ISSN 1938-6737, Vol. 68, no 1, p. 1791-1802Article in journal (Refereed)
    Abstract [en]

    High production cost is one of the major barriers to widespread commercialization of solid oxide fuel cells (SOFCs). Thermal spray techniques are a low cost alternative for the production of SOFCs. The objective of this work was to evaluate the electrochemical performance of half-cells produced by plasma spraying. The anode was deposited on a porous metallic support by atmospheric plasma spraying (APS) whereas the electrolyte was deposited by plasma spray-thin film (PS-TF) technique which can produce thin and dense coatings at high deposition rates. The cathode was deposited by screen-printing. The electrochemical tests were performed at 650-800°C. Current-voltage characteristics and impedance spectra were measured and analyzed. The impact of electrolyte composition and layer thickness on the gas tightness of the electrolyte and the area specific resistance of the cell is discussed. The results show that the applied thermal spraying techniques are a potential alternative for producing SOFCs. © The Electrochemical Society.

  • 257.
    Gutnichenko, O
    et al.
    Division of Production and Materials Engineering, Lund University, Lund, S-22100, Sweden.
    Agic, Adnan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. SECO Tools AB, Björnbacksvägen 2, Fagersta, 73782, Sweden.
    Ståhl, J-E
    Division of Production and Materials Engineering, Lund University, Lund, S-22100, Sweden.
    Modeling of Force Build-up Process and Optimization of Tool Geometry when Intermittent Turning2017In: Procedia CIRP, ISSN 2212-8271, E-ISSN 2212-8271, Vol. 58, p. 393-398Article in journal (Refereed)
    Abstract [en]

    Intermittent turning the slotted workpieces is always accompanied with a high impact load of the machine tool during the entry phase of the cutting edge. The process leads to a strong dynamic response of the system and results in vibrations arose and potential tool life and surface finish issues. The present study addresses the modeling of cutting force build-up process with further optimization of cutting edge geometry where tooltip overshoot during the tool entry is selected as an objective function. The model takes into consideration the interaction between three units of the machine tool such as a tool, toolpost, and workpiece as well as an influence of the process on the system's dynamics.

  • 258.
    Haas, Sylvio
    et al.
    Photon Science, DESY, Hamburg, Germany.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Fisk, Martin
    Malmö University, Materials Science and Applied Mathematics, Malmö, Sweden Division of Solid Mechanics, Lund University, Lund, Sweden.
    Park, Jun-Sang
    X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, USA.
    Lienert, Ulrich
    Photon Science, DESY, Hamburg, Germany.
    Correlation of precipitate evolution with Vickers hardness in Haynes® 282® superalloy: In-situ high-energy SAXS/WAXS investigation2018In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 11, p. 250-258Article in journal (Refereed)
    Abstract [en]

    The aim of this work is to characterize the precipitation kinetics in Haynes® 282® superalloys using in-situ high-energy Small Angle X-ray Scattering (SAXS) together with Wide Angle X-ray Scattering (WAXS). The phases identified by WAXS include γ (matrix), γ′ (hardening precipitates), MC (metallic carbides), and M23C6/M6C (secondary metallic carbides). The γ'-precipitates are spheroids with a diameter of several nanometres, depending on the temperature and ageing time. From the SAXS data, quantitative parameters such as volume fraction, number density and inter-particle distance were determined and correlated with ex-situ Vickers microhardness measurements. The strengthening components associated with precipitates and solid solutions are differentiated using the measured Vickers microhardness and SAXS model parameters. A square root dependence between strengthening attributable to the precipitates and the product of volume fraction and mean precipitate radius is found. The solid solution strengthening component correlates with the total volume fraction of precipitates.

  • 259.
    Hagqvist, Petter
    University West, Department of Engineering Science, Division of Automation Systems. Department of Signals and Systems Automatic control, Automation and Mechatronics, Chalmers University of Technology.
    Non-intrusive instrumentation and estimation: Applications for control of an additive manufacturing process2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    For integration of additive manufacturing into industrial production, there is a need for capable yet robust automation solutions. Such solutions are to ensure consistent process outputs, both with regard to deposit geometry and material properties. In this thesis, instrumentation and control solutions have been investigated for the laser metal wire deposition additive manufacturing process. This particular process is promising with regard to e.g. high deposition rates and negligible material waste. However, due to its inherent dynamics, it requires automatic control in order to prove competitive. A large number of process parameters affect the resulting quality of the deposit. Successful control of these parameters is crucial for turning laser metal wire deposition into an industrially tractable process. This requires relevant and reliable process information such as the temperature of the deposit and the positioning of the tool relative to the workpiece. Due to the particular requirements of instrumenting the process, only non-intrusive measurement methods are viable. In this thesis, such measurement solutions are presented that advance automatic control of the laser metal wire deposition. In response to the need for accurate temperature measurements for the process, a new temperature measurement method has been developed. By adopting the novel concept of temporal, rather than spectral, constraints for solving the multispectral pyrometry problem, it opens up for temperature measurements which compensates for e.g. an oxidising deposit. For maintaining a good deposition process in laser metal wire deposition, control of tool position and wire feed rate is required. Based on measurements of resistance through the weld pool, a simple yet well performing control system is presented in this thesis. The control system obtains geometrical input information from resistance measurements made in-situ, and feeds this information to an iterative learning controller. This results in a robust, cheap and practical control solution for laser metal wire deposition, which is suitable for industrial use and that can easily be retrofitted to existing equipment.

  • 260.
    Hagqvist, Petter
    et al.
    University West, Department of Engineering Science, Division of Automation Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Automation Systems.
    Heralic, Almir
    GKN Aerospace.
    Automation of a laser welding system for additive manufacturing2015In: Proceedings of the 2015 IEEE International Conference on Automation Science and Engineering / [ed] Kazuhiro Saitou, Univ. of Michigan, IEEE, 2015, p. 900-905Conference paper (Refereed)
    Abstract [en]

    This paper presents the benefits and challenges ofusing a standard robotised laser welding cell for additive manufacturing(AM). Additive manufacturing, sometimes denoted3D-printing or rapid prototyping, has lately met strong interestin several areas of society, and a variety of technologies andmaterials have been in focus. The current paper summarisesautomation efforts for AM of advanced aero engine componentsusing high power laser with welding optics as power source formelting metal wire and using an industrial robot for obtaininga 3-dimensional feature shape. The challenges are related to theprocess itself encountering high and repeated temperatures withmelting and solidification of the metal as the main players. Themajor research solutions discussed in this paper are relatedto automation issues for obtaining a stable process and tohave control of the temperatures and temperature changes thatthe metals encounter during the process. The solutions aresuccessfully implemented in an industrial laser welding cell.

  • 261.
    Hagqvist, Petter
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Heralic, Almir
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Lennartson, Bengt
    University West, Department of Engineering Science, Division of Manufacturing Processes. University West, Department of Engineering Science, Division of Production System. Chalmers.
    Resistance based iterative learning control of additive manufacturing with wire2015In: Mechatronics (Oxford), ISSN 0957-4158, E-ISSN 1873-4006, Vol. 31, p. 116-123Article in journal (Refereed)
    Abstract [en]

    This paper presents successful feed forward control of additive manufacturing of fully dense metallic components. The study is a refinement of former control solutions of the process, providing more robust and industrially acceptable measurement techniques. The system uses a solid state laser that melts metal wire, which in turn is deposited and solidified to build the desired solid feature on a substrate. The process is inherently subjected to disturbances that might hinder consecutive layers to be deposited appropriately. The control action is a modified wire feed rate depending on the surface of the deposited former layer, in this case measured as a resistance. The resistance of the wire stick-out and the weld pool has shown to give an accurate measure of the process stability, and a solution is proposed on how to measure it. By controlling the wire feed rate based on the resistance measure, the next layer surface can be made more even. A second order iterative learning control algorithm is used for determining the wire feed rate, and the solution is implemented and validated in an industrial setting for building a single bead wall in titanium alloy. A comparison is made between a controlled and an uncontrolled situation when a relevant disturbance is introduced throughout all layers. The controller proves to successfully mitigate these disturbances and maintain stable deposition while the uncontrolled deposition fails.

  • 262.
    Hagqvist, Petter
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Kristoffersen, Hans
    Swerea IVF AB, Box 104, SE-431 22 Mölndal, Sweden.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Temperature Monitoring of Induction Hardening Using Spectral Pyrometry2014In: Proceedings of the 6th International Swedish Production Symposium 2014 / [ed] Stahre, Johan, Johansson, Björn & Björkman, Mats, 2014, p. 1-7Conference paper (Refereed)
    Abstract [en]

    In this study, a recently developed multispectral temperature measurement method is applied for temperature monitoring of induction hardening of steel. An industry-like induction heating process is used for evaluating the method and an automatic calibration procedure is presented. Thermocouples and a conventional pyrometer are used for comparison, showing that the multispectral method gives more accurate results than the conventional pyrometer. These results confirm that the multispectral method is well suited for accurate, non-contacting temperature measurements for induction hardening processes. Enabling measurements which have previously not been possible. This enables fast selection of process parameters which can improve productivity.

  • 263.
    Hameed, Pearlin
    et al.
    Centre for Biomaterials, Cellular & Molecular Theranostics (CBCMT), Vellore Institute of Technology, Vellore, 632014, India.
    Gopal, Vasanth
    Centre for Biomaterials, Cellular & Molecular Theranostics (CBCMT), Vellore Institute of Technology, Vellore, 632014, India; Department of Physics, School of Advanced Sciences, Vellore Institute of Technology, Vellore, 632014, India.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Ganvir, Ashish
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sen, Dwaipayan
    Centre for Biomaterials, Cellular & Molecular Theranostics (CBCMT), Vellore Institute of Technology, Vellore, 632014, India.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Manivasagam, Geetha
    Centre for Biomaterials, Cellular & Molecular Theranostics (CBCMT), Vellore Institute of Technology, Vellore, 632014, India.
    Axial Suspension Plasma Spraying: An ultimate technique to tailor Ti6Al4V surface with HAp for orthopaedic applications2019In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 173, p. 806-815Article in journal (Refereed)
    Abstract [en]

    Dissolution of atmospheric plasma sprayed (APS) hydroxyapatite (HAp) coatings on Ti-6Al-4 V medical implants have always been a challenge to overcome in the field of biomedical industry. In the present work, an attempt has been made to develop a HAp coating using a novel thermal spray process called axial suspension plasma spraying (SPS), which leads to thin adherent coatings. Two HAp coatings fabricated by APS (P1 and P2) and four SPS HAp coatings (S1, S2, S3 and S4) produced with varying spraying parameters were characterized in terms of (1) microstructure, porosity, hardness, adhesion strength, contact angle and phase purity; (2) corrosion resistance in 10% Fetal bovine serum (FBS); (3) in-vitro cell adherence and cell viability using human umbilical cord blood-derived mesenchymal stem cells (hMSCs). Amongst different APS and SPS coatings, P1 and S3 exhibited superior properties. S3 coating developed using SPS exhibited 1.3 times higher adhesion strength when compared to APS coating (P1) and 9.5 times higher corrosion resistance than P1. In addition, both S3 and P1 exhibited comparatively higher biocompatibility as evidenced by the presence of more than 92% viable hMSCs. © 2018 Elsevier B.V.

  • 264.
    Hanning, Fabian
    et al.
    Chalmers University of Technology, Department of Materials and Manufacturing Technology, Gothenburg, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    A Review of Strain Age Cracking in Nickel Based Superalloys2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. 1-7Conference paper (Refereed)
    Abstract [en]

    This paper reviews the literature with emphasis on strain age cracking, a cracking phenomenon that can occur during welding or heat treatment of precipitation hardening superalloys. The influence of chemical composition in terms of e.g. hardening elements and impurities, microstructure of base material and weld zone, precipitation-induced stress development, welding heat input, restraint and post weld heat treatment (PWHT) conditions is discussed and related to the cracking susceptibility of different nickel based superalloys. Furthermore, an overview on available testing methods is presented and scrutinized. As of now, neither a standardized nor universally applicable procedure is available where the now existing tests generally can be divided into two groups; procedures representing actual welds usually providing qualitative comparisons under specified conditions, and simulative tests like those based on the Gleeble® system which can provide fundamental insight into the ongoing mechanisms.

  • 265.
    Hanning, Fabian
    et al.
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    The Influence of Base Metal Microstructure on Weld Cracking in Manually GTA Repair Welded Cast ATI 718Plus®2018In: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives: Energy, Aerospace, and Industrial Applications / [ed] Ott, E., Liu, X., Andersson, J., Bi, Z., Bockenstedt, K., Dempster, I., Groh, J., Heck, K., Jablonski, P., Kaplan, M., Nagahama, D. and Sudbrack, C., 2018, p. 917-928Conference paper (Refereed)
    Abstract [en]

    The effect of base metal conditions on the weld cracking response of cast ATI 718Plus® was investigated in this study, comparing as cast microstructure with pseudo hot isostatic pressing (HIP) heat treatments at 1120, 1160 and 1190 °C for dwell times of 4 and 24 h. Linear grooves have been filled using multipass manual gas tungsten arc welding (GTAW) to simulate repair welding conditions. Metallographic investigation revealed cracks in both base metal heat affected zone and fusion zone layers. The heat treatment temperatures chosen below, at and above incipient laves melting temperature of ATI 718Plus® were found to have an effect on weld cracking behaviour, with an increased average total crack length in the base metal heat affected zone for both 1160 and 1190 °C as compared to the as cast condition and the 1120 °C homogenization treatment. The increase in cracking susceptibility shows a correlation with the amount of Nb-rich secondary phases, with lower amounts leading to crack concentration to solidification grain boundaries present from the casting process, increasing the average crack length.

  • 266.
    Hanning, Fabian
    et al.
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Weldability of wrought Haynes 282 repair welded using manual gas tungsten arc welding2018In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 62, no 1, p. 39-45Article in journal (Refereed)
    Abstract [en]

    The ability of the precipitation hardening superalloy Haynes® 282® to be repaired by multi-pass gas tungsten arc welding is investigated in this study. The repair welding has been carried out on forged discs having four pre weld heat treatments, resulting in different grain sizes and precipitate structures of the base material. Another set of discs has additionally been put through a post weld heat treatment. The tendency to form cracks in the heat-affected zone and the fusion zone has been investigated metallographically. No cracks in the base metal heat-affected zone were found,whereas solidification cracks were present in the weld fusion zone of all tested conditions. While high heat input during welding increased cracking by a factor of 1.5, none of the heat treatments had a measurable influence on the cracking behaviour. Voids with solid state crack-like appearance turned out tobe aluminium-rich oxides being present from the deposition of previous weld deposit layers.

  • 267.
    Hanning, Fabian
    et al.
    Chalmers University of Technology,Department of Industrial and Materials Science, S-Gothenburg, 41296, Sweden.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Measurement of the thermal cycle in the base metal heat affected zone of cast ATI ® 718Plus TM during manual multi-pass TIG welding2018In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 25, p. 443-449Article in journal (Refereed)
    Abstract [en]

    This paper presents a method to acquire thermal data in the base metal heat affected zone (HAZ) during manual multi-pass TIG welding of ATI ® 718Plus TM , representing conditions close to an actual repair welding operation. Thermocouples were mounted in different locations along side walls of linear grooves to record temperature data. The thermal cycling was found to be largely independent of location within the HAZ. The recorded temperatures were below the incipient laves melting temperature, indicating that the current test setup requires optimisation to study HAZ liquation. Based on the results of this study, a modified thermocouple mounting technique is proposed. © 2018 Elsevier B.V. All rights reserved.

  • 268.
    Harati, Ebrahim
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Fatigue strength of welds in 800 MPa yield strength steels: Effects of weld toe geometry and residual stress2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nowadays there is a strong demand for lighter vehicles in order to increase the pay load. Through this the specific fuel consumption is decreased, the amount of greenhouse gases is lowered and the transport economy improved. One possibility to optimize the weight is to make the components from high strength steels and join them by welding. Welding is the main joining method for fabrication of a large proportion of all engineering structures. Many components experience fatigue loading during all or part of their life time and welded connections are often the prime location of fatigue failure.Fatigue fracture in welded structures often initiates at the weld toe as aconsequence of large residual stresses and changes in geometry acting as stress concentrators. The objective of this research is to increase the understanding of the factors that control fatigue life in welded components made from very high strength steels with a yield strength of more than 800 MPa. In particular the influences of the local weld toe geometry (weld toe radius and angle) and residual stress on fatigue life have been studied. Residual stresses have been varied by welding with conventional as well as Low Transformation Temperature (LTT) filler materials. The three non-destructive techniques Weld Impression Analysis (WIA), Laser Scanning Profiling (LSP) and Structured Light Projection (SLP) have been applied to evaluate the weld toe geometry.Results suggest that all three methods could be used successfully to measure the weld toe radius and angle, but the obtained data are dependent on the evaluation procedure. WIA seems to be a suitable and economical choice when the aim is just finding the radius. However, SLP is a good method to fast obtain a threedimensional image of the weld profile, which also makes it more suitable for quality control in production. It was also found that the use of LTTconsumables increased fatigue life and that residual stress has a relatively larger influence than the weld toe geometry on fatigue strength of welded parts.

  • 269.
    Harati, Ebrahim
    University West, Department of Engineering Science, Division of Welding Technology.
    Improving fatigue properties of welded high strength steels2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In recent years a strong interest has been expressed to produce lighter structures.One possible solution to reduce the weight is to utilize high strength steels and use welding as the joining method. Many components experience fatigue loadingduring all or part of their life time and welded connections are often the prime location of fatigue failure. This becomes more critical in welded high strength steels as fatigue strength of welds does not increase by increasing the steel strength. A possible solution to overcome this issue is to use fatigue improvement methods.The main objectives of this project are, therefore, to increase understanding of the factors that control fatigue life and to investigate how the fatigue strength improvement methods; high frequency mechanical impact (HFMI) treatment and use of Low Transformation Temperature (LTT) consumables will affect fatigue properties of welds in high strength steels. In this regard, Gas Metal Arc Welding(GMAW) was used to produce butt and fillet welds using LTT or conventional fillers in steels with yield strengths ranging from 650-1021 MPa and T-joint weldsin a steel with 1300 MPa yield strength. The effect of HFMI on fatigue strength of the welds in 1300 MPa yield strength steels was also investigated. Butt and fillet welds in 650-1021 MPa steels were fatigue tested under constant amplitude tensile loading with a stress ratio of 0.1 while T-joints were fatigue tested under constant amplitude fully reversed bending load with a stress ratio of -1. The nominal stress approach was used for fatigue strength evaluation of butt and fillet welds whereas the effective notch stress approach was used in case of T-joints. Relative effectsof the main parameters such as residual stress and weld toe geometry influencing fatigue strength of welds were evaluated. Residual stresses were measured using X-ray diffraction for as-welded and HFMI treated welds. Neutron diffraction was additionally used to investigate the near surface residual stress distribution in 1300 MPa LTT welds.Results showed that use of LTT consumables increased fatigue strength of welds in steels with yield strengths ranging from 650-1021 MPa. For butt welds, the vii characteristic fatigue strength (FAT) of LTT welds at 2 million cycles was up to46% higher when compared to corresponding welds made with conventional fillermaterials. In fillet welds, a maximum improvement of 132% was achieved when using LTT wires. The increase in fatigue strength was attributed to the lower tensile residual stresses or even compressive stresses produced close to the weldtoe in LTT welds. Weld metals with martensite transformation start temperatures around 200 °C produced the highest fatigue strength. In 1300 MPa yield strength steel, similar FAT of 287 MPa was observed for LTT welds and 306 MPa for conventional welds, both much higher than the IIW FATvalue of 225 MPa. The relative transformation temperatures of the base and weldmetals, specimen geometry and loading type are possible reasons why the fatigue strength was not improved by use of LTT wires. Neutron diffraction showed that the LTT consumable was capable of inducing near surface compressive residual stresses in all directions at the weld toe. It was additionally found that there arevery steep stress gradients both transverse to the weld toe line and in the depth direction, at the weld toe. Due to difficulties to accurately measure residual stresses locally at the weld toe most often in the literature and recommendations residual stresses a few millimetre away from the weld toe are related to fatigue properties. However, this research shows that caution must be used when relating these to fatigue strength, in particular for LTT welds, as stress in the base materiala few millimetre from the weld toe can be very different from the stress locally at the weld toe.HFMI increased the mean fatigue strength of conventional welds in 1300 MPa steels about 26% and of LTT welds by 13%. It increased the weld toe radius slightly but produced a more uniform geometry along the treated weld toes. Large compressive residual stresses, especially in the longitudinal direction, were introduced adjacent to the weld toe for both LTT and conventional treated welds. It was concluded that the increase in fatigue strength by HFMI treatment is due to the combined effect of weld toe geometry modification, increase in surface hardness and introduction of compressive residual stresses in the treated region.It was concluded that the residual stress has a relatively larger influence than the weld toe geometry on fatigue strength of welds. This is based on the observation that a moderate decrease in residual stress of about 15% at the 300 MPa stress level had the same effect on fatigue strength as increasing the weld toe radius by approximately 85% from 1.4 mm to 2.6 mm, in fillet welds. Also, a higher fatigue strength was observed for HFMI treated conventional welds compared to as welded samples having similar weld toe radii but with different residual stresses.

  • 270.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Dalaei, Kamellia
    ESAB AB, Lindholmsallen 9, 40227 Gothenburg.
    Applicability of Low Transformation Temperature welding consumables to increase fatigue strength of welded high strength steels2017In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 97, p. 39-47Article in journal (Refereed)
    Abstract [en]

    Application of Low Transformation Temperature (LTT) consumables in welding is a recent approach to increase the fatigue strength of welds. In this paper high strength steels with yield strengths ranging from 650-1021 MPa were fillet and butt welded using different LTT and conventional consumables. The effects of weld metal chemical composition on phase transformation temperatures, residual stresses and fatigue strength were investigated. Lower transformation start temperatures and hence lower tensile or even compressive residual stresses were obtained close to the weld toe for LTT welds. Fatigue testing showed very good results for all combinations of LTT consumables and high strength steels with varying strength levels. For butt welds, the characteristic fatigue strength (FAT) of LTT welds at 2 million cycles was up to 46% higher when compared to corresponding welds made with conventional filler materials. In fillet welds, a minimum FAT improvement of 34% and a maximum improvement of 132% was achieved when using LTT wires. It is concluded that different LTT consumables can successfully be employed to increase fatigue strength of welds in high strength steels with yield strength up to 1021 MPa. Weld metals with martensite transformation start temperatures close to 200°C result in the highest fatigue strengths.

  • 271.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Dalaei, Kamellia
    ESAB AB, Gothenburg.
    The relative effects of residual stresses and weld toe geometry on fatigue life of weldments2015In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 77, p. 160-165Article in journal (Refereed)
    Abstract [en]

    The weld toe is one of the most probable fatigue crack initiation sites in welded components. In this paper, the relative influences of residual stresses and weld toe geometry on the fatigue life of cruciform welds was studied. Fatigue strength of cruciform welds produced using Low Transformation Temperature (LTT) filler material has been compared to that of welds produced with a conventional filler material. LTT welds had higher fatigue strength than conventional welds. A moderate decrease in residual stress of about 15% at the 300 MPa stress level had the same effect on fatigue strength as increasing the weld toe radius by approximately 85% from 1.4 mm to 2.6 mm. It was concluded that residual stress had a relatively larger influence than the weld toe geometry on fatigue strength.

  • 272.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Pirling, Thilo
    Institut Max von Laue-Paul Langevin, 6 rue Jules Horowitz, BP156, F-38042 Grenoble, France.
    Dalaei, Kamellia
    ESAB AB, Lindholmsallen 9, 40227 Gothenburg, Sweden.
    Neutron Diffraction Evaluation of Near Surface Residual Stresses at Welds in 1300 MPa Yield Strength Steel2017In: Materials, E-ISSN 1996-1944, Vol. 10, no 6, p. 1-14, article id E593Article in journal (Refereed)
    Abstract [en]

    Evaluation of residual stress in the weld toe region is of critical importance. In this paper, the residual stress distribution both near the surface and in depth around the weld toe was investigated using neutron diffraction, complemented with X-ray diffraction. Measurements were done on a 1300 MPa yield strength steel welded using a Low Transformation Temperature (LTT) consumable. Near surface residual stresses, as close as 39 µm below the surface, were measured using neutron diffraction and evaluated by applying a near surface data correction technique. Very steep surface stress gradients within 0.5 mm of the surface were found both at the weld toe and 2 mm into the heat affected zone (HAZ). Neutron results showed that the LTT consumable was capable of inducing near surface compressive residual stresses in all directions at the weld toe. It is concluded that there are very steep stress gradients both transverse to the weld toe line and in the depth direction, at the weld toe in LTT welds. Residual stress in the base material a few millimeters from the weld toe can be very different from the stress at the weld toe. Care must, therefore, be exercised when relating the residual stress to fatigue strength in LTT welds.

  • 273.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Ottosson, Mattias
    University West, Department of Engineering Science, Division of Automation Systems.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Non-destructive measurement of weld toe radius using Weld Impression Analysis, Laser Scanning Profiling and Structured Light Projection methods2014In: Proceedings of First International Conference on Welding and Non Destructive Testing (ICWNDT2014), 2014, p. 1-8Conference paper (Refereed)
  • 274.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Improving fatigue strength of welded 1300 MPa yield strength steel using HFMI treatment or LTT fillers2017In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 79, no September, p. 64-74Article in journal (Refereed)
    Abstract [en]

    Fatigue improvement techniques are widely used to increase fatigue strength of welded high strength steels. In this paper high frequency mechanical impact (HFMI) and a Low Transformation Temperature (LTT) filler material were employed to investigate the effect on fatigue strength of welded 1300 MPa yield strength steel. Fatigue testing was done under fully reversed, constant amplitude bending load on T-joint samples. Fatigue strength of LTT welds was the same as for welds produced using a conventional filler material. However, HFMI treatment increased the mean fatigue strength of conventional welds about 26% and of LTT welds about 13%. Similar distributions of residual stresses and almost the same weld toe radii were observed for welds produced using LTT and conventional consumables. HFMI increased the weld toe radius slightly and produced a more uniform geometry along the treated weld toes. Relatively large compressive residual stresses, adjacent to the weld toe were produced and the surface hardness was increased in the treated region for conventional welds after HFMI. For this specific combination of weld geometry, steel strength and loading conditions HFMI treatment gave higher fatigue strength than LTT consumables.

  • 275.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    The measurement of weld toe radius using three non-destructive techniques2014In: Proceedings of The 6th International Swedish Production Symposium 201416-18 September 2014 / [ed] Johan Stahre, Björn Johansson,Mats Björkman, 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

    The three non-destructive methods Weld Impression Analysis, Laser Scanning Profiling and Structured Light Projection were employed to measure the weld toe radius of fillet welds. All three methods could be used succesfully but results are dependent on evaluation procedure. The results show that the weld toe geometry cannot be considered uniform and varies along the weld. It was also found that the measured weld toe radii do not vary significantly with minor variations ofthe surface profile orientation.

  • 276.
    Harati, Ebrahim
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Widmark, Mattias
    Material Technology, Volvo Group Trucks Technology, Gothenburg, Sweden.
    Effect of high frequency mechanical impact treatment on fatigue strength of welded 1300 MPa yield strength steel2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 92, p. 96-106Article in journal (Refereed)
    Abstract [en]

    High frequency mechanical impact (HFMI) is a recent post weld treatment method which can be employed to increase the fatigue strength of welded components. In this paper the fatigue strength of as-welded and HFMI treated fillet welds in a 1300 MPa yield strength steel was compared. Fatigue testing was done under fully reversed, constant amplitude bending load. Finite element analysis was used to calculate the stress distribution in the weld toe region to permit evaluation of the fatigue data with the effective notch stress approach. As-welded samples showed a mean fatigue strength of 353 MPa and a characteristic fatigue strength of 306 MPa. HFMI treatment increased the mean fatigue strength by 26% and the characteristic fatigue strengths by 3%. The weld toe radii in as-welded condition were large. HFMI only increased the weld toe radii slightly but resulted in a more uniform weld toe geometry along the weld. A depth of indentation in the base metal in the range of 0.15–0.19 mm and a width of indentation in the range of 2.5–3 mm, were achieved. Maximum compressive residual stresses of about 800 MPa in the longitudinal and 250 MPa in the transverse direction were introduced by HFMI treatment, adjacent to the weld toe. The surface hardness was increased in the entire HFMI treated region. It is concluded that the increase in fatigue strength is due to the combined effects of the weld toe geometry modification, increase in surface hardness and creation of compressive residual stresses in the treated region.

  • 277.
    Hattinger, Monika
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Organizational e-learning readiness for technology enhanced competence initiatives in the manufacturing industry2015In: Global e-learning / [ed] Landeta Etxeberria, Ana, Madrid: Udima , 2015, 2Chapter in book (Other academic)
  • 278.
    Hattinger, Monika
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Eriksson, Kristina
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Action Design Research: Design of e-WIL for the Manufacturing Industry2015In: The 2015 Americas Conference on Information Systems (AMCIS 2015): Proceedings, 2015, p. 1-14Conference paper (Refereed)
    Abstract [en]

    This paper reports on a design process of e-learning courses for competence development of experienced employees in the manufacturing industry. Through a cross- organizational collaborative action design research project the aim was to design e-learning courses at university level to support work-integrated learning. Two design- and learning cycles were evaluated over two years. The first cycle identified challenges that were applied to a pilot course in Industrial automation. From evaluation of this course we derived design principles applied to two further courses in Machining and Negotiation skills. The results from our empirical data suggest general principles as competence mapping work, collaborative manufacturing e-WIL cases and interactive learning technologies for design of e-WIL courses as boundary crossing activities to reach transformative learning integrated in the manufacturing industry.

  • 279.
    Heralic, Almir
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Charles Murgau, Corinne
    University West, Department of Engineering Science, Division of Production Engineering.
    Dzevad, Imamovic
    Volvo Aero Coorporation.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Lennartson, Bengt
    Dep of signal and systems, Chalmers.
    Towards stable high-speed metal-wire deposition, Part I: Parameter studyIn: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387Article in journal (Refereed)
  • 280.
    Heralic, Almir
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Production Engineering.
    Ottosson, Mattias
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Lennartson, Bengt
    Chalmers.
    Control Design for Automation of Robotized Laser Metal-Wire Deposition2008In: Proceedings of the 17th IFAC World Congress, International Federation of Automatic Control , 2008, p. 14785-14791Conference paper (Other academic)
    Abstract [en]

    In this paper a novel approach towards automation of robotized laser metal-wire deposition (RLMwD) is described. The RLMwD technique is being developed at University West in cooperation with Swedish industry for solid freeform fabrication of fully dense metal structures. The process utilizes robotized fibre laser welding and metal wire filler material, together with a layered manufacturing method, to create metal structures directly from a CAD drawing. The RLMwD process can also be used for repair or modification of existing components. This paper faces the challenge of designing a control system for maintaining stable process variables, such as a constant layer height and a stable component temperature, during the entire manufacturing process. Several problems are identified and discussed in the paper, e.g. the difficulty of obtaining the bead height in the weld pool environment. The case study is a repair application for stamping tools, where worn out trim edges are to be repaired. Issues regarding the control design, system identification, and the practical implementation of this application are discussed.

  • 281.
    Heralic, Almir
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Christiansson, Anna-Karin
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Ottosson, Mattias
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Hurtig, Kjell
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Lennartson, Bengt
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Automation of Robotized Laser Metal-Wire Deposition2007In: Proceedings of the ninth IASTED International Conference on Control and Applications: Montreal, Canada, ACTA Press , 2007, p. ID 658-075-Conference paper (Refereed)
  • 282.
    Heralic, Almir
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Christiansson, Anna-Karin
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Ottosson, Mattias
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Hurtig, Kjell
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Lennartson, Bengt
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Freeform Fabrication using Laser Metal-wire Deposition2007In: Proceedings from the 1st Swedish Production Symposium: 28-30 August, Gothenburg, Sweden, 2007, p. session 1.2-Conference paper (Other academic)
  • 283.
    Heralic, Almir
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Ottosson, Mattias
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Production Engineering.
    Kristiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Visual feed-back for operator interaction in robotized laser metal deposition2008In: Proceedings of the 22nd International Conference on Surface Modification Technologies SMT22: Held at University West, Trollhättan, Sweden September 22-24, 2008 / [ed] T.S. Sudarshan & Per Nylen, 2008, p. 297-304Conference paper (Other academic)
  • 284.
    Hoier, P.
    et al.
    Chalmers University of Technology, Department of Materials and Manufacturing Technology,GothenburgSweden.
    Klement, Uta
    Chalmers University of Technology, Department of Materials and Manufacturing Technology,GothenburgSweden.
    Tamil Alagan, Nageswaran
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Beno, Tomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Wretland, A.
    KN Aerospace Engine Systems AB,Trollhättan,Sweden.
    Characterization of tool wear when machining alloy 718 with high-pressure cooling using conventional and surface-modified WC-Co tools2017In: Journal of Superhard Materials, ISSN 1063-4576, Vol. 39, no 3, p. 178-185Article in journal (Refereed)
    Abstract [en]

    Coolant supplied by high pressure into the cutting zone has shown the lower thermal loads on the tool when machining difficult-to-cut materials as the Alloy 718. In this study, we investigate how the combination of high-pressure cooling and tool-surface modifications can lead to further improvements regarding tool life. The general approach is to enhance the coolant-tool interaction by increasing the contact area. Therefore, we machined cooling features into flank and rake faces of commercially available cemented tungsten carbide inserts. In this way, the surface area was increased by similar to 12%. After the cutting tests, the tools were analyzed by scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. Compared with conventional tools, the tool modifications reduced the flank wear by 45% for the investigated cutting parameters. Furthermore, we were able to significantly increase the cutting speed and feed rate without failure of the tool. The investigated surface modifications have great potential to enhance the productivity of metal cutting processes.

  • 285.
    Hoier, Philipp
    et al.
    Chalmers University of Technology, Department of Materials and Manufacturing Technology, Gothenburg, Sweden.
    Klement, Uta
    Chalmers University of Technology, Department of Materials and Manufacturing Technology, Gothenburg, Sweden.
    Tamil Alagan, Nageswaran
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Beno, Tomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Wretland, Anders
    GKN Aerospace Engine Systems AB, Trollhättan, Sweden.
    Characterization of tool wear when machining Alloy 718 with high pressure cooling using conventional and surface-modified WC-Co tools2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. 1-7Conference paper (Refereed)
    Abstract [en]

    Coolant supplied by high pressure into the cutting zone has shown to lower thermal loads on the tool when machining difficult-to-cut materials as Alloy 718. In this study, we investigate how the combination of high pressure cooling and tool-surface modifications can lead to further improvements regarding tool life. The general approach is to enhance the coolant-tool interaction by increasing the contact area. Therefore, we machined cooling features into flank and rake faces of commercially available cemented tungsten carbide inserts. In this way, the surface area was increased by ~ 12%. After the cutting tests, the tools were analyzed by scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. Compared with conventional tools, the tool modifications reduced the flank wear by 45% for the investigated cutting parameters. Furthermore, we were able to significantly increase the cutting speed and feed rate without failure of the tool. The investigated surface modifications have great potential to enhance the productivityof metal cutting processes.

  • 286.
    Hoier, Philipp
    et al.
    Chalmers University of Technology, Department of Industrial and Materials Science,Gothenburg, Sweden.
    Klement, Uta
    Chalmers University of Technology, Department of Industrial and Materials Science,Gothenburg, Sweden.
    Tamil Alagan, Nageswaran
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Beno, Tomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Wretland, Anders
    GKN Aerospace Engine Systems AB, Trollhättan, Sweden.
    Flank wear characteristics of WC-Co tools when turning Alloy 718 with high-pressure coolant supply2017In: Journal of Manufacturing Processes, ISSN 1526-6125, Vol. 30, no Supplement C, p. 116-123Article in journal (Refereed)
    Abstract [en]

    In the present study, the tool wear mechanisms of uncoated cemented tungsten carbide (WC-Co) tools during machining Alloy 718 with high-pressure coolant supply are investigated. Worn flank faces are analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). With increasing spiral cutting length, larger areas on the tool surface are subjected to erosion of Co-binder by the coolant jet impact. Moreover, the amount and morphology of workpiece-precipitates adhered on worn flank surfaces are influenced significantly by the extent of flank wear land (due to increasing spiral cutting length). The reasons for the obtained results are addressed with respect to the underlying mechanisms. Possible implications for the tool wear behavior are discussed.

  • 287.
    Holmberg, Jonas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Surface integrity on post processed alloy 718 after nonconventional machining2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    There is a strong industrial driving force to find alternative production technologies in order to make the production of aero engine components of superalloys even more efficient than it is today. Introducing new and nonconventional machining technologies allows taking a giant leap to increase the material removal rate and thereby drastically increase the productivity. However, the end result is to meet the requirements set for today's machined surfaces.The present work has been dedicated to improving the knowledge of how the non-conventional machining methods Abrasive Water Jet Machining, AWJM, Laser Beam Machining, LBM, and Electrical Discharge Machining, EDM, affect the surface integrity. The aim has been to understand how the surface integrity could be altered to an acceptable level. The results of this work have shown that both EDM and AWJM are two possible candidates but EDM is the better alternative; mainly due to the method's ability to machine complex geometries. It has further been shown that both methods require post processing in order to clean the surface and to improve the topography and for the case of EDM ageneration of compressive residual stresses are also needed.Three cold working post processes have been evaluated in order to attain this: shot peening, grit blasting and high pressure water jet cleaning, HPWJC. There sults showed that a combination of two post processes is required in order to reach the specified level of surface integrity in terms of cleaning and generating compressive residual stresses and low surface roughness. The method of high pressure water jet cleaning was the most effective method for removing the EDM wire residuals, and shot peening generated the highest compressive residual stresses as well as improved the surface topography.To summarise: the most promising production flow alternative using nonconventional machining would be EDM followed by post processing using HPWJC and shot peening.

  • 288.
    Holmberg, Jonas
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Swerea IVF AB, Argongatan 30, Mölndal SE-431 53, Sweden.
    Prieto, Juan Manuel Rodri­guez
    Luleå University of Technology, Division of Mechanics of Solid Materials Department of Engineering Sciences and Mathematics. Luleå SE-971 87, Sweden.
    Berglund, Johan
    Swerea IVF AB, Argongatan 30, Mölndal SE-431 53, Sweden.
    Sveboda, Ales
    Luleå University of Technology, Division of Mechanics of Solid Materials Department of Engineering Sciences and Mathematics. Luleå SE-971 87, Sweden.
    Jonsén, Pärr
    Luleå University of Technology, Division of Mechanics of Solid Materials Department of Engineering Sciences and Mathematics. Luleå SE-971 87, Sweden.
    Experimental and PFEM-simulations of residual stresses from turning tests of a cylindrical Ti-6Al-4V shaft2018In: Procedia CIRP, ISSN 2212-8271, E-ISSN 2212-8271, Vol. 71, p. 144-149Article in journal (Refereed)
    Abstract [en]

    Alloy Ti-6Al-4V is a frequently used material in aero space applications due the high strength and low weight. This material is however often considered as a difficult to machine alloy due to several material properties such as the inherent characteristics of high hot hardness and strength which is causing an increased deformation of the cutting tool during machining. The thermal properties also cause a low thermal diffusion from locally high temperatures in the cutting zone that allows for reaction to the tool material resulting in increased tool wear. Predicting the behavior of machining of this alloy is therefore essential when selecting machining tools or machining strategies. If the surface integrity is predicted, the influence of different machining parameters could be studied using Particle Finite Element (PFEM)-simulations. In this investigation the influence from cutting speed and feed during turning on the residual stresses has been measured using x-ray diffraction and compared to PFEM-simulations. The results showed that cutting speed and feed have great impact on the residual stress state. The measured cutting force showed a strong correlation especially to the cutting feed. The microstructure, observed in SEM, showed highly deformed grains at the surface from the impact of the turning operation and the full width half maximum from the XDR measurements distinguish a clear impact from different cutting speed and feed which differed most for the higher feed rate. The experimental measurements of the residual stresses and the PFEM simulations did however not correlate. The surface stresses as well as the sign of the residuals stresses differed which might be due to the material model used and the assumption of using a Coulomb friction model that might not represent the cutting conditions in the investigated case.

  • 289.
    Holmberg, Jonas
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Swerea IVF AB, Argongatan 30, 431 22 Mölndal, Sweden.
    Steuwer, Axel
    Nelson Mandela Metropolitan University, Gardham Avenue, 6031 Port Elizabeth, South Africa.
    Stormvinter, Albin
    Swerea IVF AB, Argongatan 30, 431 22 Mölndal, Sweden.
    Kristofferson, Hans
    Swerea IVF AB, Argongatan 30, 431 22 Mölndal, Sweden.
    Haakanen, Merja
    Stresstech OY, Tikkutehtaantie 1, 40 800 Vaajakoski, Finland.
    Berglund, Johan
    Swerea IVF AB, Argongatan 30, 431 22 Mölndal, Sweden.
    Residual stress state in an induction hardened steel bar determined by synchrotron- and neutron diffraction compared to results from lab-XRD2016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 667, p. 199-207Article in journal (Refereed)
    Abstract [en]

    Induction hardening is a relatively rapid heat treatment method to increase mechanical properties of steel components. However, results from FE-simulation of the induction hardening process show that a tensile stress peak will build up in the transition zone in order to balance the high compressive stresses close to the surface. This tensile stress peak is located in the transition zone between the hardened zone and the core material. The main objective with this investigation has been to non-destructively validate the residual stress state throughout an induction hardened component. Thereby, allowing to experimentally confirming the existence and magnitude of the tensile stress peak arising from rapid heat treatment. For this purpose a cylindrical steel bar of grade C45 was induction hardened and characterised regarding the microstructure, hardness, hardening depth and residual stresses. This investigation shows that a combined measurement with synchrotron/neutron diffraction is well suited to non-destructively measure the strains through the steel bar of a diameter of 20 mm and thereby making it possible to calculate the residual stress profile. The result verified the high compressive stresses at the surface which rapidly changes to tensile stresses in the transition zone resulting in a large tensile stress peak. Measured stresses by conventional lab-XRD showed however that at depths below 1.5 mm the stresses were lower compared to the synchrotron and neutron data. This is believed to be an effect of stress relaxation from the layer removal. The FE-simulation predicts the depth of the tensile stress peak well but exaggerates the magnitude compared to the measured results by synchrotron/neutron measurements. This is an important knowledge when designing the component and the heat treatment process since this tensile stress peak will have great impact on the mechanical properties of the final component.

  • 290.
    Holmberg, Jonas
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Swerea-IVF AB, 431 22, Mölndal, Sweden.
    Wretland, Anders
    GKN Aerospace Engine Systems AB, Trollhättan, Sweden.
    Berglund, Johan
    Grit Blasting for Removal of Recast Layer from EDM Process on Inconel 718 Shaft: An Evaluation of Surface Integrity2016In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 25, no 12, p. 5540-5550Article in journal (Refereed)
    Abstract [en]

    The heat generated during EDM melts the work material and thereby allows large amounts to be removed,but an unfavorable surface of a recast layer (RCL) will also be created. This layer has entirely different properties compared to the bulk. Hence, it is of great interest to efficiently remove this layer and to verify that it has been removed. The main objective of this work has been to study the efficiency of grit blasting forremoval of RCL on an EDM aero space shaft. Additionally, x-ray fluorescence (XRF) has been evaluated asa nondestructive measurement to determine RCL presence. The results show that the grit-blasting processing parameters have strong influence on the ability to remove RCL and at the same time introduce beneficial compressive stresses even after short exposure time. Longer exposure will remove the RCL fromthe surface but also increase the risk that a larger amount of the blasting medium will get stuck into the surface. This investigation shows that a short exposure time in combination with a short grit-blasting nozzle distance is the most preferable process setting. It was further found that handheld XRF equipment can be used as a nondestructive measurement in order to evaluate the amount of RCL present on an EDM surface.This was realized by analyzing the residual elements from the EDM wire.

  • 291.
    Holmberg, Jonas
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Swerea-IVF AB, 431 22, Mölndal, Sweden.
    Wretland, Anders
    GKN Aerospace Engine Systems AB, Trollhättan, Sweden.
    Berglund, Johan
    Swerea IVF AB, Argongatan 30, 431 22 Mölndal, Sweden.
    Beno, Tomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Evaluation of surface integrity after high energy machining with EDM, Laser Beam Machining and Abrasive Water Jet Machining of Alloy 7182019In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 100, no 5-8, p. 1575-1591Article in journal (Refereed)
    Abstract [en]

    Development of future aero engine components based on new design strategies utilising topological optimisation and additive manufacturing has in the past years become a reality. This allows for designs that involve geometries of "free form" surfaces and material combinations that could be difficult to machine using conventional milling. Hence, alternative manufacturing routes using non-conventional high energy methods are interesting to explore. In this investigation, the three high energy machining methods abrasive water jet machining (AWJM), electrical discharge machining (EDM) and laser beam machining (LBM) have been compared in terms of surface integrity to the reference, a ball nosed end milled surface. The results showed great influence on the surface integrity from the different machining methods. It was concluded that AWJM resulted in the highest quality regarding surface integrity properties with compressive residual stresses in the surface region and a low surface roughness with texture from the abrasive erosion. Further, it was shown that EDM resulted in shallow tensile residual stresses in the surface and an isotropic surface texture with higher surface roughness. However, even though both methods could be considered as possible alternatives to conventional milling they require post processing. The reason is that the surfaces need to be cleaned from either abrasive medium from AWJM or recast layer from EDM. It was further concluded that LBM should not be considered as an alternative in this case due to the deep detrimental impact from the machining process.Keywords

  • 292.
    Holmberg, Jonas
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Manufacturing Swerea IVF AB Mölndal Sweden.
    Wretland, Anders
    GKN Aerospace Sweden AB Trollhättan Sweden.
    Berglund, Johan
    Manufacturing Swerea IVF AB Mölndal Sweden.
    Beno, Tomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Surface integrity after post processing of EDM processed Inconel 718 shaft2018In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 95, no 5-8, p. 2325-2337Article in journal (Refereed)
    Abstract [en]

    Electrical discharge machining (EDM) is considered as an efficient alternative to conventional material removal concepts that allows for much higher material removal rates. However, EDM generates unwanted features such as re-cast layer (RCL), tensile residual stresses and a rough surface. In order to recover the surface integrity, different post processes has been compared: high-pressure water jet (HPWJ), grit blasting (GB) and shot peening (SP). Surface integrity has been evaluated regarding microstructure, residual stresses, chemical content and surface roughness. The results showed that a combination of two post processes is required in order to restore an EDM processed surface of discontinuous islands of RCL. HPWJ was superior for removing RCL closely followed by grit blasting. However, grit blasting showed embedded grit blasting abrasive into the surface. Regarding surface roughness, it was shown that both grit blasting and HPWJ caused a roughening of the surface topography while shot peening generates a comparably smoother surface. All three post processes showed compressive residual stresses in the surface where shot peening generated the highest amplitude and penetration depths. However, the microstructure close to the surface revealed that shot peening had generated cracks parallel to the surface. The results strongly state how important it is to evaluate the surface at each of the different subsequent process steps in order to avoid initiation of cracks.

  • 293. Holmstrand, T
    et al.
    Mrdjanov, N.
    Barsoum, Z.
    Åstrand, Erik
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Fatigue life assessment of improved joints welded with alternative welding techniques2014In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 42, no July, p. 10-21Article in journal (Refereed)
    Abstract [en]

    In this study, the fatigue life improvement by adopting the toe weaving technique on nonload carrying cruciform welded joints has been investigated. Fatigue testing was conducted on two batches of specimens welded using double-pass manual welding. One batch had a straight second pass and the other was weaved. The influence of different weaving shape parameters was analyzed by performing crack growth analyses. The fatigue testing shows a slightly improved fatigue life for the two different batches compared to as-welded joints; the improvement is similar for both batches. The crack growth analysis concludes that the batch with the straight second pass should provide slightly higher fatigue life compared to the toe weaved batch. Measurements show a presence of undercuts in the vicinity of the crack initiation site. Nonetheless, an increased fatigue life is obtained, due to the low flank angle created during welding of the second pass, which reduces the stress concentration in the weld toe, prolonging the fatigue life.

  • 294.
    Hosseini, S.B.
    et al.
    Chalmers University of Technology, Department of Materials and Manufacturing Technology.
    Beno, Tomas
    University West, Department of Engineering Science, Division of Production Engineering. University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Johansson, S
    Lektronik, Ing.f:a, 424 49 Angered, Sweden .
    Klement, Uta
    Chalmers University of Technology, Department of Materials and Manufacturing Technology.
    Kaminski, J
    Chalmers University of Technology, Department of Materials and Manufacturing Technology.
    Ryttberg, K.
    AB SKF, 415 50 Gothenburg.
    Cutting temperatures during hard turning: Measurements and effects on white layer formation in AISI 521002014In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, no 6, p. 1293-1300Article in journal (Refereed)
    Abstract [en]

    This paper concerns the temperature evolution during white layer formation induced by hard turning of martensitic and bainitic hardened AISI 52100 steel, as well as the effects of cutting temperatures and surface cooling rates on the microstructure and properties of the induced white layers. The cutting temperatures were measured using a high speed two-colour pyrometer, equipped with an optical fibre allowing for temperature measurements at the cutting edge. Depending on the machining conditions, white layers were shown to have formed both above and well below the parent austenitic transformation temperature, Ac1, of about 750 C. Thus at least two different mechanisms, phase transformation above the Ac1 (thermally) and severe plastic deformation below the Ac1 (mechanically), have been active during white layer formation. In the case of the predominantly thermally induced white layers, the cutting temperatures were above 900 C, while for the predominantly mechanically induced white layers the cutting temperatures were approximately 550 C. The surface cooling rates during hard turning were shown to be as high as 104-105 C/s for cutting speeds between 30 and 260 m/min independent of whether the studied microstructure was martensitic or bainitic. Adding the results from the cutting temperature measurements to previous results on the retained austenite contents and residual stresses of the white layers, it can be summarised that thermally induced white layers contain significantly higher amounts of retained austenite compared to the unaffected material and display high tensile residual stresses. On the contrary, in the case of white layers formed mainly due to severe plastic deformation, no retained austenite could be measured and the surface and subsurface residual stresses were compressive. © 2014 Elsevier B.V.

  • 295.
    Hosseini, Seyed B.
    et al.
    Chalmers University of Technology, Department of Materials and Manufacturing Technology.
    Beno, Tomas
    University West, Department of Engineering Science, Division of Production Engineering. University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Johansson, S
    Lektronik, Ing.f:a, 424 49 Angered.
    Klement, Uta
    Chalmers University of Technology, Department of Materials and Manufacturing Technology.
    Kaminski, J
    Chalmers University of Technology, Department of Materials and Manufacturing Technology.
    Ryttberg, K.
    AB SKF, 415 50 Gothenburg.
    A Methodology for Temperature Correction When Using Two-Color Pyrometers: Compensation for Surface Topography and Material2014In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 54, no 3, p. 369-377Article in journal (Refereed)
    Abstract [en]

    In this investigation, the applicability of the two-color pyrometer technique for temperature measurements in dry hard turning of AISI 52100 steel was studied, where both machined surfaces as well as cutting tools were considered. The impacts of differing hard turned surface topography on the two-color pyrometer readings was studied by conducting temperature measurements on reference samples created using cutting tools with different degrees of tool flank wear. In order to conduct measurements in a controlled environment, a specially designed furnace was developed in which the samples were heated step-wise up to 1,000 °C in a protective atmosphere. At each testing temperature, the temperatures measured by the two-color pyrometer were compared with temperatures recorded by thermocouples. For all materials and surfaces as studied here, the two-color pyrometer generally recorded significantly lower temperatures than the thermocouples; for the hard turned surfaces, depending on the surface topography, the temperatures were as much as 20 % lower and for the CBN cutting tools, 13 % lower. To be able to use the two-color pyrometer technique for temperature measurements in hard turning of AISI 52100 steel, a linear approximation function was determined resulting in three unique equations, one for each of the studied materials and surfaces. By using the developed approximation function, the measured cutting temperatures can be adjusted to compensate for differing materials or surface topographies for comparable machining conditions. Even though the proposed equations are unique for the hard turning conditions as studied here, the proposed methodology can be applied to determine the temperature compensation required for other surface topographies, as well as other materials. © 2013 Society for Experimental Mechanics.

  • 296.
    Hosseini, Vahid
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of multiple welding cycles on microstructure and corrosion resistance of a super duplex stainless steel2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Super duplex stainless steel (SDSS) has found a wide use in demanding applications such as offshore, chemical and petrochemical industries thanks to its excellent combination of mechanical properties and corrosion resistance. Welding of SDSS, however, is associated with the risk of precipitation of secondary phases and formation of excessive amounts of ferrite in the weld metal and heat affected zone. The present study was therefore aimed at gaining knowledge about the effect of multiple welding thermal cycles on the microstructure and possible sensitization to corrosion of welds in SDSS.Controlled and repeatable thermal cycles were produced by robotic welding. Oneto four autogenous TIG-remelting passes were applied on 2507 type SDSS plates using low or high heat inputs with pure argon as shielding gas. Thermal cycles were recorded using several thermocouples attached to the plates. Thermodynamic calculations and temperature field modelling were performed in order to understand the microstructural development and to predict the pitting corrosion resistance. Etching revealed the formation of different zones with characteristic microstructures: the fused weld zone (WZ) and the heat affected zone composed of the fusion boundary zone (FBZ), next to the fusion boundary, and further out Zone 1 (Z1) and Zone 2 (Z2). The WZ had a high content of ferrite and often nitrides which increased with increasing number of passes and decreasing heati nput. Nitrogen content of the WZ decreased from 0.28 wt.% to 0.17 wt.% after four passes of low heat input and to 0.10 wt.% after four passes of high heatinput. The FBZ was reheated to high peak temperatures (near melting point) and contained equiaxed ferrite grains with austenite and nitrides. Zone 1 was free from precipitates and the ferrite content was similar to that of the unaffected base material. Sigma phase precipitated only in zone 2, which was heated to peak temperatures in the range of approximately 828°C to 1028°C. The content of sigma phase increased with the number of passes and increasing heat input. 

    All locations, except Z1, were susceptible to local corrosion after multiplere heating. Thermodynamic calculations predicted that a post weld heat treatment could restore the corrosion resistance of the FBZ and Z2. However, the pitting resistance of the WZ cannot be improved significantly due to the nitrogen loss. Steady state and linear fitting approaches were therefore employed to predict nitrogen loss in autogenous TIG welding with argon as shielding gas. Two practical formulas were derived giving nitrogen loss as functions of initial nitrogen content and arc energy both predicting a larger loss for higher heat input and higher base material nitrogen content. A practical recommendation based on the present study is that it is beneficial to perform welding with a minimum number of passes even if this results in a higherheat input as multiple reheating strongly promotes formation of deleterious phases.

  • 297.
    Hosseini, Vahid
    University West, Department of Engineering Science, Division of Welding Technology.
    Super duplex stainless steels: Microstructure and propertiesof physically simulated base and weld metal2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    High-temperature processing and application of super duplex stainless steel(SDSS) are associated with the risk of changes in the ferrite/austenite balance and precipitation of secondary phases. This study was therefore aimed at improving knowledge about effects of thermal cycles on the microstructure and properties of SDSS base and weld metal. Controlled and repeatable thermal cycles were physically simulated using the innovative multiple TIG reheating/remelting and the arc heat treatment techniques. In the first technique, one to four autogenous TIG-remelting passes were applied. During arc heat treatment, a stationary arc was applied on a disc mounted on a water-cooled chamber thereby subjecting the material to a steady state temperature gradient from 0.5 minute to 600 minutes. Microstructures and properties were assessed and linked to thermal history through thermal cycle analysis, thermodynamic calculations and temperature field modelling, Remelting studies showed that nitrogen loss from the melt pool was a function of arc energy and initial nitrogen content and could cause highly ferritic microstructures. Heat affected zones were sensitized by nitride formation next to the fusion boundary and sigma phase precipitation in regions subjected to peak temperatures of 828-1028°C. Accumulated time in the critical temperature range, peak temperature and the number of thermal cycles are the most relevant criteria when evaluating the risk of sigma phase precipitation. Arc heat treatment produced graded microstructures in SDSS base and weld metal with the formation of a ferritic region at high temperature due to solid-state nitrogen loss, precipitation of sigma, chi, nitrides, and R-phase with different morphologies at 550-1010°C and spinodal decomposition below 500°C. This caused sensitization and/or increased hardness and embrittlement. Results were summarized as time-temperature-precipitation and properties diagrams for base and weld metal together with guidelines for processing and welding of SDSS.

  • 298.
    Hosseini, Vahid A.
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Aashuri, H.
    Materials Science and Engineering Dep., Sharif University of Technology, Tehran, Iran.
    Kokabi, A. H.
    Materials Science and Engineering Dep., Sharif University of Technology, Tehran, Iran.
    Study of the effect of tool geometry on semisolid stir welding of a AZ91 magnesium alloy2015In: Proceedings of the 18th International Conference on Joining Materials, JOM-Institute , 2015, p. 1-10Conference paper (Refereed)
    Abstract [en]

    Semisolid stir welding is a newly developed method suitable for joining of the magnesium alloy AZ91. In this study, the effect of tool geometries on the joint properties such as bending strength and the occurrence of porosity are studied. A 2 mm-thick Mg-25%Zn interlayer was placed between two AZ91 plates and the plate was heated up to 530°C before joining. At this temperature, when both the interlayer and the base metal were in the semisolid state, a stirrer was introduced into the joint. Drill-tip and round shape stirrer tools were employed at three different stirring rates. Welds produced with the two methods showed similar properties in the shear punch test. However, using the round tool geometry resulted in welds with excellent bending strength closely matching that of the base metal especially at the highest stirring rate. The improved properties when using the round tool was a result of the formation of a very fine and uniform microstructure with a low content of porosity.

  • 299.
    Hosseini, Vahid A.
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes. Innovatum AB, Trollhättan, Sweden.
    Valiente Bermejo, María Asunción
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Gårdstam, Johannes
    Swerea KIMAB AB, Kista, Sweden.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Influence of multiple thermal cycles on microstructure of heat-affected zone in TIG-welded super duplex stainless steel2016In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 60, no 2, p. 233-245Article in journal (Refereed)
    Abstract [en]

    The influence of heat input and multiple welding cycles on the microstructure of the heat-affected zone in autogenously TIG-welded 6 mm 2507 type super duplex stainless steel plates was investigated. In order to produce multiple thermal cycles, one to four pass bead-on-plate welds were made with arc energies of 0.47 and 1.08 kJ/mm, corresponding to heat inputs of 0.37 and 0.87 kJ/mm. Several thermocouples were attached to record thermal cycles on the front and back sides of the plates. Finite element modelling was successfully done to map and correlate measured and calculated peak temperatures. Only minor changes were seen in the ferrite content at 1 and 2 mm from the fusion boundary. Nitrides formed in all passes of the low heat input samples in a region next to the fusion boundary, but only after the third and fourth passes of the high heat input samples. Sigma phase precipitated only in a zone heated to a peak temperature in the range of approximately 828 to 1028 °C. Multiple reheating was found to promote precipitation of sigma phase relatively more than slower cooling. A precipitation free zone was observed between the nitride and sigma phase bands. The precipitation behaviour could be understood from equilibrium phase diagrams, evaluation of local thermal cycles and by correlating results from the modelling and measurements of peak temperatures. It is suggested that the peak temperature, the accumulated time in the critical temperature range between approximately 828 and 1028 °C, and the number of thermal cycles are the most relevant criteria when evaluating the risk of sigma phase formation.

  • 300.
    Hosseini, Vahid A.
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Manufacturing Processes. Swerea KIMAB AB, Kista, Sweden.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nitrogen loss and effects on microstructure in multipass TIG welding of a super duplex stainless steel2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 98, no May, p. 88-97Article in journal (Refereed)
    Abstract [en]

    Nitrogen loss is an important phenomenon in welding of super duplex stainless steels. In this study, a super duplex stainless steel was autogenously TIG-welded with one to four bead-on-plate passes with low or high heat inputs using pure argon shielding gas. The goal was to monitor nitrogen content and microstructure for each weld pass. Nitrogen content, measured by wavelength dispersive X-ray spectrometry, was after four passes reduced from 0.28 wt% in the base metal to 0.17 wt% and 0.10 wt% in low and high heat input samples, respectively. Nitrogen loss resulted in a more ferritic structure with larger grains and nitride precipitates. The ferrite grain width markedly increased with increasing number of passes and heat input. Ferrite content increased from 55% in base metal to 75% at low and 79% at high heat inputs after four passes. An increasing amount of nitrides were seen with increasing number of weld passes. An equation was suggested for calculation of the final nitrogen content of the weld metal as functions of initial nitrogen content and arc energy. Acceptable ferrite contents were seen for one or two passes. The recommendation is to use nitrogen in shielding gas and proper filler metals.

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