Electron beam powder bed fusion (EBPBF) is a beneficial processing route to fabricate Ti6Al4V alloy for aerospace applications due to its relatively low lead time and the possibility of topology optimization. The dry sliding wear behavior of EBPBF-Ti6Al4V against steel- and alumina-counterballs from room temperature (RT) to 500 °C was investigated to evaluate the influence of EBPBF processing and microstructure on the wear properties for broadening the application criteria of this lightweight alloy. The wear tests revealed that the wear rate decreased with increasing temperature due to formation of stable oxide glaze layer. This study reveals elevated temperature sliding wear behavior, wear mechanisms and microstructural changes below the wear track of EBPBF Ti6Al4V alloy against steel and alumina counterbodies. 

Gray cast iron (GCI) is a popular automotive brake disc material by virtue of its high melting point as well as excellent heat storage and damping capability. GCI is also attractive because of its good castability and machinability, combined with its cost-effectiveness. Although several lightweight alloys have been explored as alternatives in an attempt to achieve weight reduction, their widespread use has been limited by low melting point and high inherent costs. Therefore, GCI is still the preferred material for brake discs due to its robust performance. However, poor corrosion resistance and excessive wear of brake disc material during service continue to be areas of concern, with the latter leading to brake emissions in the form of dust and particulate matter that have adverse effects on human health. With the exhaust emission norms becoming increasingly stringent, it is important to address the problem of brake disc wear without compromising the braking performance of the material. Surface treatment of GCI brake discs in the form of a suitable coating represents a promising solution to this problem. This paper reviews the different coating technologies and materials that have been traditionally used and examines the prospects of some emergent thermal spray technologies, along with the industrial implications of adopting them for brake disc applications. © 2019 by the authors.

In a machining operation, self-excited vibration called chatter resulting from the interaction of a workpiece, a tool, and a machine is limiting manufacturers in selecting cutting process parameters that give the desired surface finish at a higher material removal rate. Thisresearch paper aimed to add some control over its impact on surface roughness by establishing a simulation model of the surface topography. The simulation was done by incorporating time-domain simulation of the cutting process based on the theory of machine and Z-buffer geometrical modelling technique. Z-buffer modelling technique applied by representing the workpiece as a Z-buffer model and by discretely dividing the cutting-edge displacement along the tool path. The main purpose of the time domain simulation was to get information about the tool displacement relative to the workpiece along the tool path to conduct z-buffering.

The influence of chatter on surface roughness was investigated on floor end milling by selecting a different combination of depth of cut and spindle speed keeping the feed rate constant. The resulting surface roughness of the simulated surface was analysed and described quantitatively by taking the arithmetic mean height (Sa) and maximum height (Sz) as a candidate for a real surface roughness measurement. The simulated surface model results were compared to the experiment. The result obtained shows that surface simulation has the potential to predict chatter and surface roughness that can be used for surface finish control when selecting cutting process parameters.

Ti-6Al-4V is one of the most widely used titanium alloys nowadays and has mechanical properties and corrosion resistance superior to that of steel and aluminum alloys. Hence, new technologies have been developed due to the fact that titanium components make excellent candidates for manufacturing from powder as new repair technologies, such as thermal spray techniques.

One of these technologies would be High Velocity Air Fuel (HVAF) thermal spray method, consisting on using a mixture of combustible and compressed air for accelerating the powder stream trough a nozzle, where little research has been done on Ti-6Al-4V coatings. Therefore, in this project, High Velocity Air Fuel sprayed coatings of Ti-6Al-4V will be studied regarding its tribological properties, mechanical properties such as hardness, microstructure analysis before and after applying different heat treatments, and finally erosion performance. All of the results will be contrasted with Ti-6Al-4V substrate and also with research from the literature in order to get a better understanding of its performance.

This thesis aims to expand the study of High Velocity Air Fuel Ti-6Al-4V coatings and to set a starting point for further studies in the repairing of this alloy by coating technology.

Metal matrix composites have huge demand in the aerospace and automobile industry due to their unique characteristics. Aluminium metal matrix composites are preferred for their specific modulus. AC Floby is well known for its automotive components. Among them,the SiCAlight brake disc is a product whose material consists of reinforced silicon carbide in aluminium metal matrix composite. The SiCAlight brake disc, as the name suggests offers a lightweight brake disc and with low to almost zero brake dust compared to conventional cast iron. Aluminium silicon carbide is difficult to machine with excessive tool wear, which increases the production cost. In this work, the main goal is to investigate the effect of cryogenic machining on aluminium metal matrix composite. Experiments were carried out by machining the aluminium silicon carbide with 20%wt using an uncoated tungsten carbide insert. Four conditions were tested namely dry, flank, rake, and dual cooling (combination of rake and flank face cooling simultaneously). This work aimed to investigate in particular the effects of different cooling conditions on tool wear compared to dry machining condition. The results showed that the dry machining had less flank wear compared to other cooling conditions at all cutting speeds. Nevertheless, cryogenic flank cooling helps in the reduction of BUE height at higher cutting speeds. Further analysis was carried out to observe the wear mechanisms. It was found that dominant wear mechanisms are abrasion and adhesion. It was also concluded that the cooling effect doesn’t have an influence on wear mechanisms. Further study led to the finding that under given cutting conditions, cutting speed has more influence than the added external cooling using liquid nitrogen.

Stability is a key indicator of the efficiency of the gas metal arc welding (GMAW) operation,and it is linked to other quality indicators like spattering and weld formation. This thesis work describes methods of assessing arc stability for selected GMAW conditions. It focuses on stability characterisation and defines the relationships between process stability and influencing factors.

Welding tests were performed using two selected transfer modes being the spray and the pulse transfer modes to characterize stability and develop processes further for better overall performance. Short circuit was not included because it exceeds the scope of thesis even though it is also of interest for ESAB to characterize stability using this mode. For the spray transfer, stability characterization was carried out by analyzing voltage disturbances (explosions) in the form of voltage peaks (negative and positive) since the explosions occurring in the arc corresponded to the voltage fluctuations during welding. These tests were performed on a sandblasted carbon steel plate, using carbon steel wire in diameter 1,0 mm, gas mixture of 82%CO22/18%Ar, and with three different voltage values (29V, 31,5V and 32,5V) and inductance control settings (0, 60 and 95). This scope of parameters was selected in order to simulate certain range of stability behavior, so it was possible to analyze the factors correlated to stability, their relevance in influencing stability, and consequently to define a calculation algorithm for the determination of stability.Also, stability was calculated and scored based on two scoring indices. The first was stability scoring based on performance character (spatter presence, hardness of arc, smoothness of process) The other was stability scoring based on regularity of the process (repeatability and steadiness of electrical parameters, variations of process disturbances, uniformity of the process). These two different stability characteristics are recognized in industry within ESAB applications, and the process regularity represents the major proportion of this characterisation.

For the pulse transfer, stability characterization was carried out by analyzing and comparing two different current waveforms in terms of evaluating effects on stability. The linear waveform, which is the conventional type of waveform, was compared to an exponential waveform (with optimised droplet detachment). Results obtained from spray arc analyses showed that stability has certain indicators that are measurable by signal and image processing, and these were further analysed. Voltage disturbances were correlated to explosions observable during the process. Actual values of positive and negative voltage peaks, voltage amplitudes, and their average values and standard deviations in selected analysed time showed to be relevant indicators to characterise stability of the process. Variations of indicated voltage signals related to explosions showed to have complex patterns in terms of their waveforms. So, all these were analysed step by step and consequently selected for characterisation (calculation of stability) in the welding conditions that were selected in the scope of this project. Exact determination of stability formula was established, and this can be further developed in ESAB conditions in terms of automating the calculation with possibility of variable setting of calculated factors and ranges for specific analysed welding conditions.

The results for the pulse arc confirmed that the exponential waveform when compared to the linear waveform showed better stability conditions. It also showed that an important factor is the duration of the base current time and its standard deviation over selected analysed time, which optimised the droplet detachment mechanism.I

n conclusion, this approach of characterizing stability has been shown to be successful in terms of having a reasonable capacity to evaluate distinct elements that are acting in the process and determining overall stability.

Thermally sprayed coatings are often used to enhance the surface properties (wear resistance, corrosion resistance, etc.) of engineering components in order to extend their performance and service lifetime. Typically, the industrial components to be coated possess complex geometries and are fabricated using different materials with varied mechanical properties such as hardness, which can influence the deposited coating’s microstructure and its subsequent performance. High-velocity air fuel (HVAF) process is a relatively new thermal spray processing technique that has shown tremendous potential to deposit high performance coatings for durable industrial components. However, so far, no studies have been reported on HVAF sprayed coating formation mechanisms in relation to the spray angle, substrate properties (hardness) and coating material composition. Therefore, this work aims to plug the above knowledge gap by systematically examining the influence of spray angle, substrate properties (hardness) and coating material composition (cermet and metallic) on coating formation. For a given coating material, the effect of spray angle and substrate material on coating properties is also investigated.

In this study, one cermet (WC-Co) and one metallic (Inconel 625) feedstock were deposited onto three different substrates (Aluminum, Steel and Hastelloy) utilizing different spray angles (40º, 50º, 60º, 70º, 80º and 90º). The preliminary effort at understanding the coating evolution involved splat characteristics analysis as well as careful examination of microstructures of coatings deposited with increasing number of passes. The coating evolution was analysed utilizing SEM/EDS, image analysis (porosity, surface coverage etc.), white light interferometry and micro-indentation technique. The deposited coating’s microstructure, porosity content, hardness, and surface roughness for Inco 625 and WC-CoCr coatings were correlated to the HVAF pro-cessing conditions (spray angle, substrate hardness). Furthermore, to determine the tribological performance, coatings were subjected to dry sliding wear test and the coefficient of friction and specific wear rates were obtained.

It was shown that, substrate material affects splat formation but not the final coating properties. Spray angle, on the other hand, displayed a strong effect on coating formationand on some of the final coating properties such as micro-hardness and coating roughness.To the author’s knowledge, this study demonstrates the first approach to investigate deposition behaviour of different HVAF coating materials.

The advent of high-throughput plasma spray systems that allow axial feeding encourages the study of using liquid feedstock for various next-generation functional applications. The current study explores the benefit of such a plasma spray system to deposit hybrid powder-suspension Al2O3-YSZ ceramic matrix composite (CMC) coatings for tribological applications. The tribological performance of the hybrid processed CMC coatings was assessed using scratch, ball-on-plate wear and erosion tests and compared with that of monolithic powder-derived Al2O3 coatings. As-deposited and tribo-tested coatings were characterized using Scanning Electron Microscopy, X-ray Diffraction and Energy Dispersive Spectroscopy to analyse their microstructure and phase constitution. The results showed that the tribological performance of the hybrid powder-suspension Al2O3-YSZ CMC coating was significantly improved by enhancing the wear resistance under scratch, dry sliding ball-on-plate and erosion tests as compared to the conventional APS deposited monolithic Al2O3 coating. About 36% decrease in the dry sliding ball-on-plate specific wear rate and up to 50% decrease in the erosion wear rate was noted in the hybrid powder-suspension Al2O3-YSZ CMC coating as compared to the conventional APS deposited monolithic Al2O3 coating. The study concludes that the hybrid powder-suspension route can create CMC coatings with unique multi-length scale microstructures which can be attractive for combining different tribological attributes in the same coating system.

Machining of aluminium matrix composites such as aluminium silicon carbide are difficult due to the presence of hard and abrasive particles of silicon carbide which causes tool wear, poor surface quality and undesirable chip formation. This work contains the study of the influence of cryogenic assisted turning operation on chip morphology, chip breakability and control on aluminium silicon carbide using uncoated tungsten carbide tool and liquid nitrogen as coolant.

It further made comparison between the results obtained from dry machining with that of cryogenic machining based on these areas of interest. Microstructural analysis of the chips obtained from the dry and cryogenic machining was performed using the light optical microscope and scanning electron microscope. Measurements of the chip thickness, chip width, tool-chip contact length, average chip length and average chip curl diameter was performed to provide insight on the chip breakability process.

Results obtained showed that chip width and thickness varied as the speed varied but did not contribute to the chip breakability. It showed that chip breakability mainly depends on the chip curl diameter and average chip length across the four-cutting condition. Observation of the rake cooling condition gave a lower chip curl diameter, favourable average chip length and short non-helical chips which are more favourable to chip breakability.The influence of the cryogenic on the chip morphology was evident in the sharp difference between the long continuous chip of the dry machining with that of the short continuous chips from the other three cooling condition, the cryogenic cooled operations formed short segmented continuous chip with some presence of micro cracks, fractures towards the chip root and delamination on the outer side of the chips which can be point of crack and stress propagation.

In conclusion, cryogenic cooling influenced the chip morphology and enhanced better chip breakability of aluminium silicon carbide especially when applied from the dual and rake face.

Corrosion is a severe threat to the longevity of automotive brake discs. Typically, protective coatings of WC-CoCr composition processed by thermal spray route are applied to provide adequate wear and corrosion resistance. However, ‘Co’-containing materials are classified as carcinogenic, which compromises the health and safety of the end-users and the coating applicators. Therefore, identifying sustainable and non-toxic alternatives to the toxic, Co-containing coatings are of interest. In addition to the coating composition, microstructure of the as-deposited coatings influences their corrosion behavior. For instance, a coating with high number of defects (cracks, pores, etc.) adversely influences their corrosion performance. The coating microstructure is intimately related to the processing route employed to manufacture the coatings. High Velocity Air Fuel (HVAF) is a relatively new thermal spray processing technique that has shown the capability to deposit high quality coatings possessing excellent corrosion performance. The primary objective of this work was to assess the corrosion behavior and degradation mechanisms of the sustainable, Fe-based coatings, High Entropy Alloy (HEA) coatings, WC-Co, Cr3C2-NiCr, substrates, and compare their performance in 3.5 wt.% NaCl environment, to find the appropriate coatings, depend on the state for the future application. The secondary objective was to examine the influence of HVAF processing conditions on the microstructure and corrosion behavior of the sustainable Fe-based coatings. Therefore, potentiodynamic polarization behavior of widely employed coatings of Cr3C2-NiCr, WC-CoCr, along with the new composition-based coatings of High Entropy Alloys (HEA), and the Fe-based chemistries (Rockit-401/R-401 and FeSP586) was examined. Additionally, the effect of HVAF processing parameters on the microstructure, porosity content, potentiodynamic polarization behaviour of the Fe-based (R-401) coatings was investigated. It was shown that the Fe-based coatings with low porosity content and minimal partially undeformed splats demonstrated superior corrosion performance. A detailed SEM analysis was performed to reveal the corrosion products.  iii Furthermore, it was shown that the coatings with highest ‘Cr’-content demonstrated superior polarization resistance among the investigated coatings. Finally, the potentiodynamic polarization performance of the investigated coatings was benchmarked with the widely employed substrates of cast iron, aluminum alloy (Al-Si) and low carbon steel. This work provides an excellent framework to rank the potentiodynamic polarization of the currently used coatings, substrates and compare them with the experimental compositions of the HEA and Fe-based alloy-based coatings in 3.5 wt.% NaCl environment.

High-entropy alloys (HEAs) represent a relatively new group of multicomponent alloys that have shown great potential for applications that require tribological and oxidation resistant properties. Consequently, thermally sprayed coatings of different HEA chemistries have also received increasing research attention. In this paper, atomized equimolar CrFeCoNi and AlCrFeCoNi feedstocks were used for high velocity air-fuel spraying to produce overlay coatings using two different nozzle configurations. The microstructure, phase constitution and hardness of the coatings were analysed. The coatings were also tested for their oxidation behaviour and their erosion resistance. The performance of the two HEA chemistries was compared with two commercial MCrAlY coatings that are well-established bond coat materials. Furthermore, an investigation was conducted to test the coatings’ performance as bond coats by applying suspension plasma sprayed yttria stabilized zirconia top coats and evaluating the thermal cycling behaviour of the thermal barrier coatings systems. The AlCrFeCoNi-coating was found to demonstrate a lower oxidation rate than CrFeCoNi. The AlCrFeCoNi chemistry also compared well with the commercial bond coat material that has been optimized after several years of development, although the former was found to form more rapid oxide scales. The HEA coatings also exhibited similar erosion resistance compared to coatings deposited with the commercial MCrAlY material.

In recent years, demand for aluminium metal matrix composites has increased in the automotive and aerospace industries due to their mechanical properties and applications. Several articles have shown that textured cutting tools can improve the tribological properties at the tool-chip interface and reduce friction, temperature, cutting forces, chip size, and tool wear. Biomimetic textures from nature can improve the performance of cutting tools by their multi-functionalities. However, scant research has been reported in machining Al-MMCs with a combination of biomimetic textured cutting inserts and liquid nitrogen coolant (LN2). In this research work, nine different texture designs on the rake face are investigated in combination with liquid nitrogen coolant in the machining of Al-MMCs (Difficult-to-Cut material). The influence of texturing on the rake face combined with the LN2 cooling is analysed by evaluating the built-up edge height, flank wear (VBmax), and flank wear area (VBarea), tool-chip contact length (TCClength), and tool-chip contact area (TCCarea). The experiment analysis performed using various tool wear methods showed that the combination of textures and LN2 coolant improved all tool wear conditions but in the dry condition, texture tools have shown no influence on all types of tool wear compared to the plain tool. The texturing on the rake face has influenced the tool-chip contact which led to a decrease in TCClength and TCCarea and therefore reduces the friction during the machining process. SEM analysis was performed on all cutting tools to observe wear mechanisms results in adhesion of workpiece material filling between textures and chipping at the cutting edges in all dry textured tools whereas using cryogenic coolant results in a dramatic reduction in chipping at cutting edges for all textured tools and the filling of adhesion material was observed to be less compared to dry condition.

The single-pulse laser hardening of a hypereutectoid steel coated by a graphite layer was investigated using a numerical/experimental approach. Experimental tests were conducted on coated samples using a fibre laser source and without any gas shielding aiming to explore the effect of laser power, pulse energy and defocusing distance on the dimensions of the hardened region. The process operating window of the discrete spot laser hardening using the graphite layer was determined through a finite element model and compared with previous results obtained on uncoated samples. For the same laser power and interaction times, an enlargement of the hardened region was found when using the graphite coating, especially when operating at the lowest laser energy level. The process operating window remains similar in shape to the one of the uncoated steel but moves towards larger hardened diameters and much larger defocusing distances. Once the maximum temperature has been fixed, a linear relationship between the hardened diameter and the defocusing distance exists. No obvious surface oxidation occurs since the graphite coating acts as a protective layer. © 2019, Springer-Verlag London Ltd., part of Springer Nature.