A strategy to improve the work-hardening behavior of Ti–6Al–4V parts produced by additive manufacturing (original) (raw)
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Journal of Alloys and Compounds, 2018
As a powder-bed-based additive manufacturing technology, selective laser melting (SLM) offers high-level flexibility and enables efficient fabrication of complex parts. In connection with complex thermal events occurring during dynamic sequential layer-by-layer deposition, the as-built material is usually hierarchical at different length scales and possesses anisotropy at each level. As a result of a moderate heating temperature of the baseplate and high cooling rates involved in the process, the as-built Ti-6Al-4V alloy has an α´ martensite microstructure. Microstructure evolution occurring during post-SLM heat treatment is strongly affected by the stability of the initial acicular martensite. The present study was aimed at developing an optimum post-SLM heat treatment scheme at a temperature below the β transus temperature, based on the understanding of microstructure evolution occurring during subtransus treatment and the resultant mechanical properties of the alloy.
Additive manufacturing and postprocessing of Ti-6Al-4V for superior mechanical properties
MRS Bulletin
The capabilities of metal additive manufacturing (AM) are evolving rapidly thanks to both increasing industry demand and improved scientifi c understanding of the process. This article provides an overview of AM of the Ti-6Al-4V alloy, which has essentially been used as a yardstick to gauge the capability of each metal AM process developed to date. It begins by summarizing the metal AM processes existing today. This is followed by a discussion of the macro-and microstructural characteristics, defects, and tensile and fatigue properties of AM Ti-6Al-4V by selective laser melting, laser metal deposition (both powder and wire), and selective electron-beam melting compared to non-AM Ti-6Al-4V. The tensile and fatigue properties of as-built AM Ti-6Al-4V (with machined or polished surfaces) can be made comparable, or even superior, to those of Ti-6Al-4V in the most commonly used millannealed condition. However, these properties can exhibit a large degree of scatter and are often anisotropic, affected by AM build orientations. Post-AM surface treatments or both the post-AM surface and heat treatments are necessary to ensure the minimum required properties and performance consistency. Future directions to further unlock the potential of AM of Ti-6Al-4V for superior and consistent mechanical properties are also discussed.
Materials
In the present study, we propose a hybrid manufacturing route to produce high-quality Ti6Al4V parts, combining additive powder laser directed energy deposition (L-DED) for manufacturing of preforms, with subsequent hot forging as a thermomechanical processing (TMP) step. After L-DED, the material was hot formed at two different temperatures (930 °C and 1070 °C) and subsequently heat-treated for stress relief annealing. Tensile tests were performed on small sub-samples, taking into account different sample orientations with respect to the L-DED build direction and resulting in very good tensile strengths and ductility properties, similar or superior to the forged material. The resulting microstructure consists of very fine grained, partially globularized alpha grains, with a mean diameter ~0.8–2.3 µm, within a beta phase matrix, constituting between 2 and 9% of the sample. After forging in the sub-beta transus temperature range, the typical L-DED microstructure was no longer discerni...
Materials
An investigation of mechanical properties of Ti6Al4V produced by additive manufacturing (AM) in the as-printed condition have been conducted and compared with wrought alloys. The AM samples were built by Selective Laser Melting (SLM) and Electron Beam Melting (EBM) in 0°, 45° and 90°—relative to horizontal direction. Similarly, the wrought samples were also cut and tested in the same directions relative to the plate rolling direction. The microstructures of the samples were significantly different on all samples. α′ martensite was observed on the SLM, acicular α on EBM and combination of both on the wrought alloy. EBM samples had higher surface roughness (Ra) compared with both SLM and wrought alloy. SLM samples were comparatively harder than wrought alloy and EBM. Tensile strength of the wrought alloy was higher in all directions except for 45°, where SLM samples showed higher strength than both EBM and wrought alloy on that direction. The ductility of the wrought alloy was consist...
Scientific Reports, 2023
The influence of heat treatment processes on microstructure, tensile and tribological properties of Ti6Al4V alloy was investigated. The specimens were heated for 30 min at 925 °C and then cooled at various rates by water quenching, air cooling, and furnace cooling. After that, the samples were aged for four hours at 600 °C. Three phases make up the microstructure: primary α-phase (α p), secondary α-phase (α s), and retained β-phase (β r). Cooling in the air and water followed by aging (AC + Aging and WQ + Aging) resulted, α s-phase precipitating inside β r-phase. The highest hardness of 35 HRC was recorded for WQ + Aging specimen due to existence of a high amount of β r-phase and precipitation of α s-phase. On the other hand, the lowest hardness of 26 HRC was obtained for the FC specimen. AC specimen achieved the highest elongation value of 14%. However, WQ + Aging specimen exhibited the highest ultimate tensile strength of 1028 MPa. For WQ + Aging and AC + Aging specimens, the ideal balance of strength and elongation was discovered. The wear resistance of solution-treated specimens was significantly improved by the aging process and 125% improvement could be achieved in WQ compared to WQ + Aging specimens.
Tensile behaviour of high temperature forged Ti-6Al-4V during in-situ heat treatments
Materials Letters
Tensile behaviour of the α+β Ti-6Al-4V titanium alloy is investigated while quenching. A new insitu thermal and mechanical treatments facility is developed. Different time-temperature and timemechanical strain histories are coupled to investigate the uniaxial tensile properties and strength of this alloy during quenching. The microstructural evolutions are reported and their influences on the mechanical behaviour are addressed.
Materials
Additively-manufactured Ti-6Al-4V (Ti64) exhibits high strength but in some cases inferior elongation to those of conventionally manufactured materials. Post-processing of additively manufactured Ti64 components is investigated to modify the mechanical properties for specific applications while still utilizing the benefits of the additive manufacturing process. The mechanical properties and fatigue resistance of Ti64 samples made by electron beam melting were tested in the as-built state. Several heat treatments (up to 1000 °C) were performed to study their effect on the microstructure and mechanical properties. Phase content during heating was tested with high reliability by neutron diffraction at Los Alamos National Laboratory. Two different hot isostatic pressings (HIP) cycles were tested, one at low temperature (780 °C), the other is at the standard temperature (920 °C). The results show that lowering the HIP holding temperature retains the fine microstructure (~1% β phase) and ...
Materials Science and Engineering: A, 2016
Electron Beam Melting (EBM), a powder bed additive layer manufacturing process, was used to produce Ti-6Al-4V specimens, whose microstructure, texture, and tensile properties were fully characterized. The microstructure, analyzed by optical microscopy, SEM/EBSD and X-ray diffraction, consists in fine α lamellae. Numerical reconstruction of the parent β phase highlighted the columnar morphology of the prior β grains, growing along the build direction upon solidification of the melt pool. The presence of grain boundary α GB along the boundaries of these prior β grains is indicative of the diffusive nature of the β-α phase transformation. Texture analysis of the reconstructed high temperature β phase revealed a strong o0014 pole in the build direction. For mechanical characterization, tensile specimens were produced using two different build themes and along several build orientations, revealing that vertically built specimens exhibit a lower yield strength than those built horizontally. The effect of post processing, either mechanical or thermal, was extensively investigated. The influence of surface finish on tensile properties was clearly highlighted. Indeed, mechanical polishing induced an increase in ductilitydue to the removal of critical surface defectsas well as a significant increase of the apparent yield strengthcaused by the removal of a $ 150 mm rough surface layer that can be considered as mechanically inefficient and not supporting any tensile load. Thermal post-treatments were performed on electron beam melted specimens, revealing that subtransus treatments induce very moderate microstructural changes, whereas supertransus treatments generate a considerably different type of microstructure, due to the fast β grain growth occurring above the transus. The heat treatments investigated in this work had a relatively moderate impact on the mechanical properties of the parts.
MATEC web of conferences, 2020
Titanium alloys, such as Ti-6Al-4V alloy, fabricated by additive manufacturing processes is a winning combination in the aeronautic field. Indeed, the high specific mechanical properties of titanium alloys with the optimized design of parts allowed by additive manufacturing should allow aircraft weight reduction. But, the long term use of Ti-6Al-4V alloy is limited to 315 °C due to high oxidation kinetics above this temperature [1]. The formation of an oxygen diffusion zone in the metal and an oxide layer above it may reduce the durability of titanium parts leading to premature failure [2, 3]. In this study, Ti-6Al-4V alloy was fabricated by Electron Beam Melting (EBM). As built microstructure evolutions after Hot Isostatic Pressure (HIP) treatment at 920 °C and 1000 bar for 2h were investigated. As built microstructure of Ti-6Al-4V fabricated by EBM was composed of Ti-α laths in a Ti-β matrix. High temperature oxidation of Ti-6Al-4V alloy at 600 °C of as-built and HIP-ed microstructures was studied. This temperature was chosen to increase oxidation kinetics and to study the influence of oxidation on tensile mechanical properties. In parallel, two other oxidation temperatures, i.e. 500 °C and 550°C allowed to access to the effect of temperature on long-term oxidation.
Journal of Materials Engineering and Performance
This paper extends our previous work to investigate the effect of heat treatment on the microstructure of Ti-6Al-4V fabricated by selective laser melting. A post-heat treatment at 930 °C for 15 min followed by three cooling rates before and after hot isostatic pressing (HIP) treatment was applied. The findings illustrated that the microstructure of the quenched samples before the HIP treatment was characterized by a mixture of α + α′ phase with a microhardness value of 336 ± 6 HV0.3. Air cooling produced a structure dominated by the α phase, with ~ 7.5% of the β phase and a microhardness value of about 330 ± 4 HV0.3. Furnace cooling led to a mixture of α phase and ~ 17% of the β phase and hardness of 327 ± 6 HV0.3. After HIP followed by post-heat treatment, acicular α′ martensite with microhardness value 377 ± 2 HV0.3 dominated the quenched specimen microstructure. Following air cooling, the microstructure consisted of a mixture of α-lamella and β with some needles of the α with a m...