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Publications (10 of 16) Show all publications
Kumara, C. (2023). Modeling and simulation of microstructures in metal additive manufacturing (1.ed.). In: Pederson, Robert, Andersson, Joel & Joshi, Shrikant V. (Ed.), Additive Manufacturing of High-Performance metallic Materials: (pp. 459-571). Elsevier
Open this publication in new window or tab >>Modeling and simulation of microstructures in metal additive manufacturing
2023 (English)In: Additive Manufacturing of High-Performance metallic Materials / [ed] Pederson, Robert, Andersson, Joel & Joshi, Shrikant V., Elsevier, 2023, 1., p. 459-571Chapter in book (Refereed)
Abstract [en]

In recent years, metal additive manufacturing (AM) has receivedincreasing interest in the field of manufacturing engineeringbecause of its attractive features compared with those ofconventional manufacturing methods. Due to the inherentnature of this process, complex thermal conditions drive phasetransformation from liquid to solid as well as phasetransformation in the solid state. A deeper and betterunderstanding of the relationships between the complex thermalconditions and the microstructure formation is vital for fullyutilizing the full potential of the AM processes. Achieving thisgoal with only an experimental approach is costly, timeconsuming, and in some cases, impractical. Consequently,computational modeling and simulation techniques areimportant complementary methods that help to achieve thisgoal. Different models are used to model different aspects of themicrostructure. The primary intention of this chapter is to givethe reader an overarching view (including a basic understanding of the formulation, limitations, applications, and challenges) ofcommonly used microstructure modeling and simulationtechniques in the context of the metal powder AM process.

Place, publisher, year, edition, pages
Elsevier, 2023 Edition: 1.
Keywords
Cellular-automata, JMAK, Mean-field, Microstructure, Modeling, Multiscale, Phase-field, Simulation
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-21075 (URN)9780323918855 (ISBN)9780323913829 (ISBN)
Available from: 2023-12-14 Created: 2023-12-14 Last updated: 2024-01-11Bibliographically approved
Adegoke, O., Kumara, C., Thuvander, M., Deirmina, F., Andersson, J., Brodin, H., . . . Pederson, R. (2023). Scanning electron microscopy and atom probe tomography characterization of laser powder bed fusion precipitation strengthening nickel-based superalloy. Micron, 171, Article ID 103472.
Open this publication in new window or tab >>Scanning electron microscopy and atom probe tomography characterization of laser powder bed fusion precipitation strengthening nickel-based superalloy
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2023 (English)In: Micron, ISSN 0968-4328, E-ISSN 1878-4291, Vol. 171, article id 103472Article in journal (Refereed) Epub ahead of print
Abstract [en]

Atom probe tomography (APT) was utilized to supplement scanning electron microscopy (SEM) characterizationof a precipitation strengthening nickel-based superalloy, Alloy 247LC, processed by laser powder bed fusion (LPBF). It was observed that the material in the as-built condition had a relatively high strength. Using both SEMand APT, it was concluded that the high strength was not attributed to the typical precipitation strengtheningeffect of γ’. In the absence of γ’ it could be reasonably inferred that the numerous black dots observed in thecells/grains with SEM were dislocations and as such should be contributing significantly to the strengthening.Thus, the current investigation demonstrated that relatively high strengthening can be attained in L-PBF even inthe absence of precipitated γ’. Even though γ’ was not precipitated, the APT analysis displayed a nanometer scalepartitioning of Cr that could be contributing to the strengthening. After heat-treatment, γ’ was precipitated and itdemonstrated the expected high strengthening behavior. Al, Ta and Ti partitioned to γ’. The strong partitioningof Ta in γ’ is indicative that the element, together with Al and Ti, was contributing to the strain-age crackingoccurring during heat-treatment. Cr, Mo and Co partitioned to the matrix γ phase. Hf, Ta, Ti and W were found inthe carbides corroborating previous reports that they are MC. 

Keywords
CM247LC, Superalloy, Additive manufacturing, atom probe tomography, Scanning electron microscopy, gamma prime
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-20014 (URN)10.1016/j.micron.2023.103472 (DOI)000999885100001 ()37146362 (PubMedID)2-s2.0-85154065448 (Scopus ID)
Available from: 2023-06-01 Created: 2023-06-01 Last updated: 2024-01-15Bibliographically approved
Zaikovska, L., Ekh, M. & Kumara, C. (2023). Virtual Testing of Synthetic Polycrystal Microstructures Predicting Elastic Properties of Additive Manufactured Alloy 718. In: Huihe Qiu, Marcello Iasiello,Yuwen Zhang (Ed.), Proceedings of the 9th World Congress on Mechanical, Chemical, and Material Engineering (MCM'23): August 06-08, 2023. Brunel University, London, United Kingdom. Paper presented at The 9 th World Congress on Mechanical, Chemical, and Material Engineering (MCM'23) Brunel University, London, United Kingdom - August 06-08, 2023. INTERNATIONAL ASET INC, Article ID ICMIE 147.
Open this publication in new window or tab >>Virtual Testing of Synthetic Polycrystal Microstructures Predicting Elastic Properties of Additive Manufactured Alloy 718
2023 (English)In: Proceedings of the 9th World Congress on Mechanical, Chemical, and Material Engineering (MCM'23): August 06-08, 2023. Brunel University, London, United Kingdom / [ed] Huihe Qiu, Marcello Iasiello,Yuwen Zhang, INTERNATIONAL ASET INC , 2023, article id ICMIE 147Conference paper, Published paper (Refereed)
Abstract [en]

Additive manufacturing (AM) is gaining significant attention in manufacturing engineering owing to its advantages compared to traditional manufacturing methods. Microstructures that result from the AM process often lead to anisotropic mechanical properties of produced components. In this study the Ni-based Alloy 718 is analysed. It has been shown that the microstructure of this polycrystalline material can be tailored to obtain different grain morphology distributions and crystallographic textures. In this paper, the reproduction of three typical microstructures, equiaxed, columnar and combined (equiaxed and columnar), are investigated to determine their elastic anisotropic properties. Virtual testing is applied on synthetic representative volume elements (RVE) for the equiaxed and columnar grain structures, and representative area element (RAE) for the combined structure. The crystal elasticity finite element method (CEFEM) is utilized to predict macroscopic elastic properties. This method allows the implementation of grain crystallographic orientations as input texture and the generation of homogenized elastic stiffness matrix predicting the directional engineering stresses of polycrystal microstructures. The comparison of the simulation results for the three microstructures studied demonstrates significant property variation. Also, the comparison of the different number of grains and various interface area cases of the combined structure shows diversity in the results presented in this study. 

Place, publisher, year, edition, pages
INTERNATIONAL ASET INC, 2023
Series
Proceedings of the World Congress on Mechanical, Chemical, and Material Engineering (MCM), ISSN 2369-8136 ; 9
Keywords
additive manufacturing, polycrystal, crystal elasticity finite element, cohesive zone, homogenization, anisotrop
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-21019 (URN)10.11159/icmie23.147 (DOI)9781990800276 (ISBN)
Conference
The 9 th World Congress on Mechanical, Chemical, and Material Engineering (MCM'23) Brunel University, London, United Kingdom - August 06-08, 2023
Note

The proceedings and related papers are all based on the open-access model, whichmeans interested individuals and institutions can access the material for free.Users are allowed to read, download, copy, distribute, print, search, or link to thefull texts of the articles in this proceedings without asking prior permission fromthe publisher or the author. This is in accordance with the BOAI definition of openaccess. 

This work was financially supported by the PODFAM project and the PRIMUS Foundation.

Available from: 2023-11-30 Created: 2023-11-30 Last updated: 2024-01-15Bibliographically approved
Kumara, C. (2020). Microstructure Modelling of Additive Manufacturing of Alloy 718. (Doctoral dissertation). Trollhättan: University West
Open this publication in new window or tab >>Microstructure Modelling of Additive Manufacturing of Alloy 718
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [sv]

In recent years, additive manufacturing (AM) of Alloy 718 has received increasing interest in the field of manufacturing engineering because of its attractive features compared with those of conventional manufacturing methods. Nevertheless, owing to the inherent nature of the process, the build material is exposed to complex thermal conditions that affect the microstructure. In addition, the post heattreatments applied to the built component further cause microstructural changes. Thus, obtaining the desired microstructure that gives the desired properties is still a challenging task. Therefore, understanding the microstructure formation during the build and subsequent post-heat treatment is important and is the objective of this thesis work.

To this end, a computational modelling approach was used that combines multiphase-field modelling with transformation kinetics modelling. Two different AM processes, laser metal powder directed energy deposition (LM-PDED) and electron beam powder bed fusion (EB-PBF), were considered in this study.Based on the modelling work, it was observed that solidification conditions (thermal gradients and cooling rates) that occur during the AM process have an impact on the as-solidified microstructure in Alloy 718 and the resultant Laves phase formation. With an increase in cooling rate, the Laves phase volume fraction becomes lower and the morphology tends to become discrete particles,which is important for resisting the formation of liquation cracks in Alloy 718. It was also found that the precipitates formed during the solidification process did not undergo any significant change during subsequent thermal cycles associated with the deposition of subsequent layers, given that the deposition of the subsequent layer does not increase the global temperature of the build to> 600 °C. If the global temperature increases above 600 °C, then phase changes are expected, depending on the temperature value. In the case of the EB-PBF process, the high build temperature maintained in the build chamber resulted in an ‘‘in situ’’ heat treatment, which had a homogenisation effect on the as-solidified microstructure because of the smaller dendrite spacing and relatively low Lavesphase size. In the case of the LM-PDED, the microsegregation of composition observed in the as-built microstructure was shown to change the equilibrium conditions and precipitation kinetics of Alloy 718. As a result, excess precipitationof γ'/γ″ and δ was observed in the interdendritic region compared with the dendrite core, depending on the type of heat treatment used.

In addition, modelling was performed to evaluate the elastic properties of EB-PBF Alloy 718. To this end, crystallographic orientation data gathered from EBSD data and single-crystal elastic constants were used. The prediction showed good agreement with published literature data. The hatch (bulk) region of the EB-PBF samples showed significant anisotropic elastic properties because of the strong crystallographic texture observed in the microstructure. The lowest Young’s modulus was observed along the build direction. Normal to the build direction, the elastic properties were shown to be isotropic. Overall, the elastic behaviour of the hatch region was similar to that of a transversely isotropic case

Place, publisher, year, edition, pages
Trollhättan: University West, 2020. p. 89
Series
PhD Thesis: University West ; 43
Keywords
Phase-Field Modelling; Additive Manufacturing; Phase Transformation; Solidification; Heat Treatment; Superalloy
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-16118 (URN)978-91-88847-83-6 (ISBN)978-91-88847-82-9 (ISBN)
Public defence
2020-12-16, 10:00 (English)
Opponent
Supervisors
Available from: 2020-12-15 Created: 2020-12-15
Balachandramurthi, A. R., Jaladurgam, N. R., Kumara, C., Hansson, T., Moverare, J., Gårdstam, J. & Pederson, R. (2020). On the microstructure of laser beam powder bed fusion alloy 718 and its influence on the low cycle fatigue behaviour. Materials, 13(22), Article ID 5198.
Open this publication in new window or tab >>On the microstructure of laser beam powder bed fusion alloy 718 and its influence on the low cycle fatigue behaviour
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2020 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 22, article id 5198Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing of Alloy 718 has become a popular subject of research in recent years. Understanding the process-microstructure-property relationship of additively manufactured Alloy 718 is crucial for maturing the technology to manufacture critical components. Fatigue behaviour is a key mechanical property that is required in applications such as gas turbines. Therefore, in the present work, low cycle fatigue behaviour of Alloy 718 manufactured by laser beam powder bed fusion process has been investigated. The material was tested in as-built condition as well as after two different thermal post-treatments. Three orientations with respect to the building direction were tested to evaluate the anisotropy. Testing was performed at room temperature under controlled amplitudes of strain. It was found that defects, inclusions, strengthening precipitates, and Young’s modulus influence the fatigue behaviour under strain-controlled conditions. The strengthening precipitates affected the deformation mechanism as well as the cycle-dependent hardening/softening behaviour. The defects and the inclusions had a detrimental effect on fatigue life. The presence of Laves phase in LB-PBF Alloy 718 did not have a detrimental effect on fatigue life. Young’s modulus was anisotropic and it contributed to the anisotropy in strain-life relationship. Pseudo-elastic stress vs. fatigue life approach could be used to handle the modulus-induced anisotropy in the strain-life relationship. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

Keywords
3D printers; Additives; Anisotropy; Defects; Industrial research; Laser beams; Microstructure, Critical component; Deformation mechanism; Fatigue behaviour; Induced anisotropy; Low cycle fatigues; Process-microstructure-property relationships; Strain-controlled; Thermal post-treatments, Fatigue of materials
National Category
Reliability and Maintenance
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-16045 (URN)10.3390/ma13225198 (DOI)000594209300001 ()2-s2.0-85096131710 (Scopus ID)
Funder
European Regional Development Fund (ERDF), 20201639Region Västra Götaland
Note

Funders: GKN. This article belongs to the Special Issue Additive Manufacturing of Superalloys

Available from: 2020-11-22 Created: 2020-11-22 Last updated: 2020-12-17Bibliographically approved
Cederberg, E., Hosseini, V., Kumara, C. & Karlsson, L. (2020). Physical simulation of additively manufactured super duplex stainless steels: microstructure and properties. Additive Manufacturing, 34, Article ID 101269.
Open this publication in new window or tab >>Physical simulation of additively manufactured super duplex stainless steels: microstructure and properties
2020 (English)In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 34, article id 101269Article in journal (Refereed) Published
Abstract [en]

The behavior of high performance super duplex stainless steel (SDSS) during additive manufacturing (AM) has been investigated using a novel arc heat treatment technique. Tungsten inert gas (TIG) arc pulses were applied on a disc shaped sample mounted on a water-cooled chamber to physically simulate AM thermal cycles. SDSS base metal and a duplicated additively manufactured structure (DAMS) were used as initial microstructures. Samples were melted one, five, or 15 times by arc heat treatment. Samples were also produced with a controlled slope down of the current to create slower cooling compared to pulsing. Microstructure characterization and modelling were performed to study the evolution of microstructure and properties with successive AM cycles. Microstructural changes were dependent on the number of reheating cycles, cooling rate, and peak temperature. In particular, the DAMS austenite morphology and fraction changed after reheating to peak temperatures above 700 °C. Nitrides and sigma were observed in the high and low temperature heat affected zones, respectively. Sensitization to corrosion was more pronounced in reheated DAMS than in the base metal. Hardness was increased more by multiple remelting/reheating than by slow cooling. It was found that AM thermal cycles significantly affect SDSS properties especially for an initial microstructure similar to that produced by AM. © 2020 Elsevier B.V.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Additives, Cooling, Corrosion, Heat affected zone, Heat treatment, Industrial heating, Inert gases, Microstructural evolution, Morphology, Thermal cycling, Initial microstructures, Manufactured structures, Microstructural changes, Microstructure and properties, Microstructure characterization, Super duplex stainless steel, Treatment techniques, Water-cooled chambers, Duplex stainless steel
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-15730 (URN)10.1016/j.addma.2020.101269 (DOI)000555845400002 ()2-s2.0-85084542579 (Scopus ID)
Funder
Knowledge Foundation, 20140130
Available from: 2020-08-24 Created: 2020-08-24 Last updated: 2021-06-11Bibliographically approved
Kumara, C., Balachandramurthi, A. R., Goel, S., Hanning, F. & Moverare, J. (2020). Toward a better understanding of phase transformations in additive manufacturing of Alloy 718. Materialia, 13, Article ID 100862.
Open this publication in new window or tab >>Toward a better understanding of phase transformations in additive manufacturing of Alloy 718
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2020 (English)In: Materialia, E-ISSN 2589-1529, Vol. 13, article id 100862Article in journal (Refereed) Published
Abstract [en]

This paper presents a discussion on the phase-transformation aspects of additively manufactured Alloy 718 during the additive manufacturing (AM) process and subsequent commonly used post-heat treatments. To this end, fundamental theoretical principles, thermodynamic and kinetics modeling, and existing literature data are employed. Two different AM processes, namely, laser-directed energy deposition and electron-beam powder-bed fusion are considered. The general aspects of phase formation during solidification and solid state in Alloy 718 are first examined, followed by a detailed discussion on phase transformations during the two processes and subsequent standard post heat-treatments. The effect of cooling rates, thermal gradients, and thermal cycling on the phase transformation in Alloy 718 during the AM processes are considered. Special attention is given to illustrate how the segregated composition during the solidification could affect the phase transformations in the Alloy 718. The information provided in this study will contribute to a better understanding of the overall process–structure–property relationship in the AM of Alloy 718 718. © 2020

Keywords
3D printers; Additives; Solidification, Cooling rates; Directed energy; General aspects; Kinetics modeling; Literature data; Overall process; Phase formations; Post heat-treatment, Heat treatment
National Category
Metallurgy and Metallic Materials Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-15772 (URN)10.1016/j.mtla.2020.100862 (DOI)000568771200009 ()2-s2.0-85089507104 (Scopus ID)
Funder
Knowledge FoundationEuropean Regional Development Fund (ERDF)
Available from: 2020-09-04 Created: 2020-09-04 Last updated: 2023-03-28Bibliographically approved
Kumara, C., Segerstark, A., Hanning, F., Dixit, N., Joshi, S. V., Moverare, J. & Nylén, P. (2019). Microstructure modelling of laser metal powder directed energy deposition of alloy 718. Additive Manufacturing, 25, 357-364
Open this publication in new window or tab >>Microstructure modelling of laser metal powder directed energy deposition of alloy 718
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2019 (English)In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 25, p. 357-364Article in journal (Refereed) Published
Abstract [en]

A multi-component and multi-phase-field modelling approach, combined with transformation kinetics modelling, was used to model microstructure evolution during laser metal powder directed energy deposition of Alloy 718 and subsequent heat treatments. Experimental temperature measurements were utilised to predict microstructural evolution during successive addition of layers. Segregation of alloying elements as well as formation of Laves and δ phase was specifically modelled. The predicted elemental concentrations were then used in transformation kinetics to estimate changes in Continuous Cooling Transformation (CCT) and Time Temperature Transformation (TTT) diagrams for Alloy 718. Modelling results showed good agreement with experimentally observed phase evolution within the microstructure. The results indicate that the approach can be a valuable tool, both for improving process understanding and for process development including subsequent heat treatment.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Phase-field, DED, Heat treatment, Thermal cycle, Modelling
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13195 (URN)10.1016/j.addma.2018.11.024 (DOI)000456378800034 ()2-s2.0-85057193791 (Scopus ID)
Funder
Knowledge Foundation
Note

Funders: European Regional Development Fund for project 3Dprint

Available from: 2018-12-12 Created: 2018-12-12 Last updated: 2021-06-11Bibliographically approved
Kumara, C., Deng, D., Hanning, F., Raanes, M., Moverare, J. & Nylén, P. (2019). Predicting the Microstructural Evolution of Electron Beam Melting of Alloy 718 with Phase-Field Modeling. Metallurgical and Materials Transactions. A, 50A(5), 2527-2537
Open this publication in new window or tab >>Predicting the Microstructural Evolution of Electron Beam Melting of Alloy 718 with Phase-Field Modeling
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2019 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50A, no 5, p. 2527-2537Article in journal (Refereed) Published
Abstract [en]

Electron beam melting (EBM) is a powder bed additive manufacturing process where a powder material is melted selectively in a layer-by-layer approach using an electron beam. EBM has some unique features during the manufacture of components with high-performance superalloys that are commonly used in gas turbines such as Alloy 718. EBM has a high deposition rate due to its high beam energy and speed, comparatively low residual stresses, and limited problems with oxidation. However, due to the layer-by-layer melting approach and high powder bed temperature, the as-built EBM Alloy 718 exhibits a microstructural gradient starting from the top of the sample. In this study, we conducted modeling to obtain a deeper understanding of microstructural development during EBM and the homogenization that occurs during manufacturing with Alloy 718. A multicomponent phase-field modeling approach was combined with transformation kinetic modeling to predict the microstructural gradient and the results were compared with experimental observations. In particular, we investigated the segregation of elements during solidification and the subsequent "in situ" homogenization heat treatment at the elevated powder bed temperature. The predicted elemental composition was then used for thermodynamic modeling to predict the changes in the continuous cooling transformation and time-temperature transformation diagrams for Alloy 718, which helped to explain the observed phase evolution within the microstructure. The results indicate that the proposed approach can be employed as a valuable tool for understanding processes and for process development, including post-heat treatments. © 2019, The Author(s).

Keywords
3D printers; Deposition rates; Electron beam melting; Electron beams; Forecasting; Gas turbines; Microstructural evolution; Solid solutions; Temperature, Additive manufacturing process; Continuous cooling transformation; Elemental compositions; Layer-by-layer approaches; Microstructural development; Microstructural gradients; Transformation diagrams; Transformation kinetics, Heat treatment
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13756 (URN)10.1007/s11661-019-05163-7 (DOI)000463991300038 ()2-s2.0-85062604965 (Scopus ID)
Funder
Knowledge FoundationEuropean Regional Development Fund (ERDF)
Available from: 2019-05-10 Created: 2019-05-10 Last updated: 2020-12-15Bibliographically approved
Kumara, C. (2018). Microstructure Modelling of Additive Manufacturing of Alloy 718. (Licentiate dissertation). Trollhättan: University West
Open this publication in new window or tab >>Microstructure Modelling of Additive Manufacturing of Alloy 718
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In recent years, additive manufacturing (AM) of Alloy 718 has received increasing interest in the field of manufacturing engineering owing to its attractive features compared to those of conventional manufacturing methods. The ability to produce complicated geometries, low cost of retooling, and control of the microstructure are some of the advantages of the AM process over traditional manufacturing methods. Nevertheless, during the building process, the build material undergoes complex thermal conditions owing to the inherent nature of the process. This results in phase transformation from liquid to solid and solid state. Thus, it creates microstructural gradients in the built objects, and as a result,heterogeneous material properties. The manufacturing process, including the following heat treatment that is used to minimise the heterogeneity, will cause the additively manufactured material to behave differently when compared to components produced by conventional manufacturing methods. Therefore, understanding the microstructure formation during the building and subsequent post-heat treatment is important, which is the objective of this work. Alloy 718 is a nickel-iron based super alloy that is widely used in the aerospace industry and in the gas turbine power plants for making components subjected tohigh temperatures. Good weldability, good mechanical properties at high temperatures, and high corrosion resistance make this alloy particularly suitablefor these applications. Nevertheless, the manufacturing of Alloy 718 components through traditional manufacturing methods is time-consuming and expensive. For example, machining of Alloy 718 to obtain the desired shape is difficult and resource-consuming, owing to significant material waste. Therefore, the application of novel non-conventional processing methods, such as AM, seems to be a promising technique for manufacturing near-net-shape complex components.In this work, microstructure modelling was carried out by using multiphase-field modelling to model the microstructure evolution in electron beam melting (EBM) and laser metal powder directed energy deposition (LMPDED) of Alloy 718 and x subsequent heat treatments. The thermal conditions that are generated during the building process were used as input to the models to predict the as-built microstructure. This as-built microstructure was then used as an input for the heat treatment simulations to predict the microstructural evolution during heat treatments. The results showed smaller dendrite arm spacing (one order of magnitude smaller than the casting material) in these additive manufactured microstructures, which creates a shorter diffusion length for the elements compared to the cast material. In EBM Alloy 718, this caused the material to have a faster homogenisation during in-situ heat treatment that resulting from the elevated powder bed temperature (> 1000 °C). In addition, the compositional segregation that occurs during solidification was shown to alter the local thermodynamic and kinetic properties of the alloy. This was observed in the predicted TTT and CCT diagrams using the JMat Pro software based on the predicted local segregated compositions from the multiphase-field models. In the LMPDED Alloy 718 samples, this resulted in the formation of δ phase in the interdendritic region during the solution heat treatment. Moreover, this resulted in different-size precipitation of γ'/γ'' in the inter-dendritic region and in the dendrite core. Themicro structure modelling predictions agreed well with the experimental observations. The proposed methodology used in this thesis work can be an appropriate tool to understand how the thermal conditions in AM affect themicro structure formation during the building process and how these as-built microstructures behave under different heat treatments.

Place, publisher, year, edition, pages
Trollhättan: University West, 2018. p. 52
Series
Licentiate Thesis: University West ; 23
Keywords
Phase-Field Modelling; Laser metal powder directed energy deposition; Electron Beam Melting; Heat Treatment; Superalloy
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13197 (URN)978-91-88847-10-2 (ISBN)978-91-88847-09-6 (ISBN)
Presentation
2018-12-12, 10:00 (English)
Supervisors
Available from: 2018-12-12 Created: 2018-12-12
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-4087-6467

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