Post-build Heat Treatments Research Articles

Synchrotron based investigation of anisotropy and microstructure of wire arc additive manufactured Grade 91 steel

Additive manufacturing (AM) rapidly produces complex shapes crucial for energy technologies and engineering designs. In this work, the microstructure and mechanical properties of additive manufactured Grade 91 (modified 9Cr–1Mo) ferritic/martensitic (FM) steel were investigated. Computational thermodynamics, synchrotron X-ray diffraction, scanning electron microscopy, and microhardness testing were utilized to quantify microstructure (crystallographic phases, microstrain), lattice parameters, and mechanical properties as functions of the build directions and post-build heat-treatment. The as-built microstructures were found to contain a large fraction of microstrain due to two-dimensional defects, and a low-carbon martensite phase (maximum value 38.4 vol%), as quantified from the X-ray diffraction analysis. It was shown that a post-build heat-treatment can effectively remove this martensitic phase and promote the formation of desired microstructures with dispersed M23C6 carbides which was consistent with Thermo-Calc predictions. From the X-ray diffraction analysis, an ∼82.5% reduction in microstrain, a 61.5% increase in the coherent grain size and complete elimination of body-centered tetragonal (BCT) phase demonstrated that an appropriate heat-treatment of AM built FM steel yields microstructures and hardness comparable to conventionally processed steel. However, based on lattice parameter and hardness map statistics, heat-treatment on the as-manufactured steel did not eliminate anisotropy.

Ultrasonic Impact Treatment (UIT) combined with powder bed fusion (PBF) process for precipitation hardened martensitic steels

High-strength martensitic stainless steels such as 17–4 PH (SS 17–4 PH) generally exhibit poor ductility and strain-hardening rates. In this study, an Ultrasonic Impact Treatment (UIT) is combined with a powder bed fusion (PBF) manufacturing process with the objective of enhancing the mechanical properties of SS 17–4 PH. UIT is introduced as a surface peening step at regular intervals during the PBF process after depositing a set of predetermined number of layers. The coupon specimens extracted from the build are then subjected to a post-build heat treatment. Then the microstructural and the mechanical properties of these specimens are characterized. The characterizations reveal that the heavy plastic deformation induced by UIT drives microstructural relaxation and recrystallization under heat treatment, reducing defects extensively. The heavy plastic deformation also drives diffusional reversion of the austenite phase during deposition and an inhibition of the martensitic phase transformation during the post-build heat treatment. As a result, the UIT specimens subjected to post-build heat treatment exhibit remarkable enhancement in ductility along with high strength and strain-hardening rate compared to the non-UIT PBF specimens under as-built condition.

Influence of heat treatment on the microstructure and creep response of additively manufactured cobalt superalloy Mar M509

ABSTRACT This work explores the influence of various post-build heat treatment procedures on the microstructural characteristics and creep response of laser powder bed fusion (L-PBF) Mar M509 superalloy. Besides MC-type carbides formed primarily during the L-PBF process, the obtained results indicate the influence of heat treatment on the nucleation of M6C and M7C3 carbides due to elemental segregation. Short-term creep-rupture tests have been conducted at 900°C/110MPa on eight specimens, each subjected to a specifically individual heat treatment procedure. Rupture times are found to be sensitive to the heat treatment applied and vary from ~178 to ~641 hours. Detailed microscopic characterisation of ruptured specimens highlights the synergistic influence of oxidation and M7C3/M6C precipitate-free zone formation on macroscopic intergranular failure facilitated by grain boundary sliding along favourably oriented small grains. Besides notable grain growth, the presence of a serrated grain boundary structure with relatively less MC-type carbide coarsening is found to offer the best creep resistance among the eight L-PBF specimens. Further improvement of the elevated temperature performance of the alloy is seen to require a focus on the L-PBF process conditions to optimise the morphology of MC carbides, as they form.

Assessing the viability of high-frequency spot melting for super duplex stainless steel 2507 via electron beam powder bed fusion

This study investigates the use of Electron Beam Powder Bed Fusion (PBF-EB) spot melting on SDSS 2507, a material known for its high tensile strength, corrosion resistance, and welding properties. Spot melting, a localized melting technique, utilize a stationary beam to create melt pools before rapidly repositioning to form new ones, offering precise control over material properties in additive manufacturing. We conducted a design of experiments with 32 samples and analysed them using SEM, XRD, EBSD, optical microscopy, nanoindentation and statistical modelling.Elevated PBF-EB processing temperatures significantly influence microstructure and phase composition. XRD analysis identified the presence of the detrimental sigma phase. EBSD analysis revealed a composition primarily consisting of austenite (63 %) and sigma phase (33.5 %), with residual ferrite (3.5 %). Statistical modelling demonstrated that a combination of spot-time, spot distance, focus offset, and layer thickness was the most reliable predictor for density while area energy proved to be the most accurate predictor for hardness, with R2adj values of 0.766 and 0.802, respectively.Our study confirms that PBF-EB is capable of processing SDSS 2507 through spot melting, resulting in high-density samples at high productivity rates. The presence of sigma phase shows a need for post build heat treatment to achieve the desired phase distribution. This research enhances the understanding of the process and also holds promise for industrial applications.

Corrigendum to “Process-structure-property modeling for postbuild heat treatment of powder bed fusion Ti-6Al-4V”

Corrigendum to “Process-structure-property modeling for postbuild heat treatment of powder bed fusion Ti-6Al-4V”

Microstructural analysis of the influences of platform preheating and post-build heat treatment on mechanical properties of laser powder bed fusion manufactured AlSi10Mg alloy

Platform preheating is a common strategy towards reducing residual stress and distortion of additively manufactured metal components by powder bed fusion – laser beam (PBF-LB) due to the lowered thermal gradient. However, platform preheating can lead to in-situ ageing for aluminium alloy components in the building process, which will affect the mechanical properties. In this work, the microstructures of PBF-LB AlSi10Mg built on preheated (150 °C) and un-preheated (ambient) platforms have been characterized in detail by various electron microscopy techniques in order to better understand the influence of platform preheating on mechanical properties. Furthermore, the influences of T5 ageing and solution treatment plus ageing (T6) on microstructure and mechanical properties have also been examined. Platform preheating to 150 °C improves strength, which is associated with the in-situ precipitation of granular or rod-shaped Si phase and needle-like β'' phase. To the best of our knowledge, this is the first report on the observation of β'' precipitates in PBF-LB Al–Si–Mg alloys in the as-built state. Upon T5 treatment, the ambient platform material exhibits significant age hardening while only marginal age hardening is observed for the 150 °C platform material. Consequently, the materials built at different platform temperatures show similar mechanical properties after T5 treatment. The age hardening response is more pronounced when a rapid solution treatment (RST, 520 °C for 10 min) is adopted instead of the conventional solution treatment (CST, 520 °C for 2 h) owing to the precipitation of a higher number density of needle-like β'' phase during ageing. The T5 treatment improves both yield strength and tensile strength, but the improvements in strength are accompanied by a reduction in ductility. On the other hand, the RST-T6 treatment substantially improves ductility and reduces the tensile strength while maintaining the yield strength for the 150 °C platform material. Based on the microstructural analysis, the influences of platform preheating and post-build heat treatment on mechanical properties of PBF-LB AlSi10Mg are discussed.

Process-structure-property modeling for postbuild heat treatment of powder bed fusion Ti-6Al-4V

Postbuild heat treatment is an important component in optimized manufacturing processing for laser beam powder bed fusion (PBF-LB) Ti-6Al-4V. The development of predictive modeling, based on the understanding of the relationships between process parameters, microstructure evolution, and mechanical properties, is a potentially key ingredient in this optimization process. In this paper, a process-structure-property (PSP) model is developed to predict the effect of postbuild heat treatment on yield strength, which is a key tensile property for PBF-LB Ti-6Al-4V. The process-structure part is developed with a focus on the prediction of solid-state phase transformation, especially dissolution of martensite during the heating phase. Subsequent tensile properties are quantified by a microstructure-sensitive yield strength model based on the predicted microstructure variables. The integrated PSP model is validated via experimentally measured phase fraction, α lath width and monotonic tensile tests on PBF-LB Ti-6Al-4V with different heat treatment temperatures, for identification of optimal process parameters.

Creep Analysis and Microstructural Evaluation of a Novel Additively Manufactured Nickel-Base Superalloy (ABD®-900AM)

Abstract Nickel-base superalloys containing 30 to 50% gamma prime (γ') volume fraction are typically used in hot section components (e.g., guide vanes or blades) for power generating gas turbines, and suitable time-dependent properties are required for long-term elevated temperature operation. Additive manufacturing (AM) has recently been used to develop complex hot-section parts utilizing innovative designs with enhanced cooling features which improve efficiencies by reducing cooling air consumption. To further explore the opportunity to improve time-dependent AM superalloys, this paper focuses on a fundamental creep study and characterization of a novel nickel-base superalloy (ABD-900AM) that was manufactured using a laser-based powder bed fusion (LBPBF) AM process. The material was subjected to a subsolvus solution anneal and multistep aging heat treatment (HT) to produce a bi-modal distribution with ∼35% volume fraction of gamma prime without postprocessing hot isostatic pressing (HIP). Microstructural characterization was carried out for the as-built and fully heat-treated structures, and a creep-rupture test program was conducted to study the resultant creep properties. Activation energies and stress exponents in addition to rupture strength and deformation resistance were compared to traditionally cast IN939 and IN738 materials. After testing, specimens were evaluated using a variety of microscopy tools to determine location and features associated with creep damage. The optimized chemistry for ABD-900AM was printed crack free and fully dense in contrast to studies on similar alloys where significant process development and postbuild heat treatments were required. High-temperature mechanical properties in the heat-treated material showed some decrease in creep strength when compared to traditional casting. This strength and rupture life debit was dependent on build orientation, but a considerable increase in creep ductility was observed due to differences in the microstructure when compared with similar AM alloys. Analysis of creep data showed differences in creep mechanisms compared to traditional cast alloys. The relationship between microstructure and creep mechanisms is discussed, and ongoing work to further improve rupture strength through heat-treatment optimization will be highlighted.

Influence of laser shock peening on the residual stresses in additively manufactured 316L by Laser Powder Bed Fusion: A combined experimental–numerical study

Detrimental subsurface tensile residual stresses occur in laser powder bed fusion (LPBF) due to significant temperature gradients during the process. Besides heat treatments, laser shock peening (LSP) is a promising technology for tailoring residual stress profiles of additively manufactured components. A multi step process simulation is applied aiming at predicting the residual stress state after applying LSP to a cuboid shaped specimen manufactured by LPBF in two different building directions as well as comparing it with a post-build heat treatment. The validity of the numerical simulation is evaluated based on comparisons of residual stresses determined by incremental hole drilling technique within different stages of the multi step process: in the as-build condition, after subsequent heat treatment as well as after applying LSP to the as-build and heat treated specimens, showing overall a good experimental-numerical agreement throughout each of the process stages. Applying a heat treatment to the as-build LPBF sample at 700 °C for 6 h showed not to be effective in eliminating the surface tensile stress entirely, reducing the tensile residual stresses by 40%. However, the application of LSP on LPBF components showed promising results: LSP was able even to convert the detrimental near surface tensile residual stresses in the LPBF component into compressive residual stresses next to the surface, which is known to be beneficial for the fatigue performance.

Using post-processing heat treatments to elucidate precipitate strengthening of additively manufactured superalloy 718

The poor machinability and extensive work hardening of Ni-based superalloys makes additive manufacturing an attractive option for producing geometrically complex components with distinct microstructures. Although previous studies show recovery of high strength at room temperature, very few studies demonstrate successful properties at elevated temperatures required for industrial applications. The objectives of this study are to present a post-build heat treatment for high strength across a wide temperature range, determine the strength contribution of nanoscale precipitating phases to the overall mechanical properties of superalloy 718, and from these, provide a comprehensive microstructure-property relationship for wrought and AM 718 to guide efforts to simulate the properties of AM components. Laser powder bed fusion–produced superalloy 718 was characterized at multiple length scales using scanning electron microscopy and transmission electron microscopy in the as-built condition and with multiple heat treatments designed to form combinations of γʹ, γʺ, and δ precipitates. Uniaxial tensile tests performed from room temperature to 600 °C on subsize specimens determined the yield strength, elastic modulus, ultimate tensile strength, fracture stress, and uniform elongation. Precipitates in this work proved to be weak barriers to dislocation motion through a dispersed barrier model, but they provided strength to the alloy through their consistent high density. The relative contribution to the yield strength from γʺ remained consistent between 48–57% of the total strength up to 600 °C, the primary influence on the high temperature strength of superalloy 718. The strength factors for γʺ and δ precipitates were found to trend inversely with tensile test temperature and may be attributable to the differences in precipitate coherency. A post-build heat treatment is recommended to maintain high strength at elevated temperatures. A quantitative microstructure-property relationship, dependent on precipitate size, density, and morphology, was derived and can estimate the yield strength across a wide temperature range applicable to the operational regimes for superalloy 718.

Unraveling the low thermal conductivity of the LPBF fabricated pure Al, AlSi12, and AlSi10Mg alloys through substrate preheating

It is essential to employ post-build heat treatment on the laser powder bed fusion (LPBF) fabricated aluminum (Al) and Al alloys due to their thermal conductivity in the as-built condition being inferior to that of the conventionally manufactured counterparts. In this study, substrate preheating (200 °C) was proposed as a solution to achieve high thermal conductivities in the as-built condition. Pure Al, AlSi12, and AlSi10Mg samples were shown to possess up to 15 %, 25 %, and 80 % higher thermal conductivity values than their non-preheated counterparts reported in the literature. An analytical analysis contingent on calculating electron mean free path in the presence of only intrinsic or a combination of intrinsic and extrinsic scattering phenomena was introduced to justify the thermal behaviors. As per micro X-ray computed tomography, EBSD analysis, and TEM investigations, the extrinsic scattering sites were found to be (i) pores, (ii) grain boundaries, (iii) cell boundaries (Al alloys), (iv) oxides (pure Al), (v) nano-size Si precipitates (AlSi10Mg), (vi) nano-size Mg 2 Si phase (AlSi10Mg), (vii) vacancies, (viii) dislocations and (ix) Si supersaturation in α-Al phase (Al alloys). The dominant scattering site(s) was found for each material based on which the difference between the obtained thermal conductivity and its corresponding nominal value or the one reported for the non-preheated condition was unraveled. The implications of the findings in this study are essential not only for Al/Al alloys but also for other metallic materials (i.e., Cu alloys), requiring high thermal conductivity in the as-built condition.

Achieving excellent strength of the LPBF additively manufactured Al–Cu–Mg composite via in-situ mixing TiB2 and solution treatment

Additively manufactured (AMed) structure with superior strength is urgently required in Al alloy engineered products. Here, we reported a laser powder bed fusion (LPBF) AMed Al–Cu–Mg composite with excellent strength obtained by in-situ mixing TiB2 and post-build heat treatment (PHT). The as-printed samples presented the bimodal structure with a refined grain size of ∼4.63 μm. The solution-treated sample exhibited an excellent combination of strength and ductility (tensile strength ∼520.3 MPa, uniform elongation ∼9%), which were 133%, 136% of the as-printed sample, respectively. Such tensile strength was the highest among all reported LPBFed 2024Al alloy/composites. In detail, the high strength can be attributed to grain boundary strengthening caused by the refined equiaxed-columnar bimodal structure, solution strengthening caused by the dissolved elements, load-bearing strengthening and Orowan-strengthening caused by TiB2 particles. Therefore, this manuscript should suggest a strategy for developing AMed high-strength aluminum composite via in-situ mixing of particles and PHT.

Intrinsic Heat Treatment of an Additively Manufactured Medium Entropy AlCrFe2Ni2-Alloy

The alloy AlCrFe2Ni2, known as medium entropy alloy (MEA, ∆S/R ~ 1.33) was processed using Laser Direct Energy Deposition (L-DED). The alloy is designed to develop a Widmanstätten type duplex microstructure following a solid state phase transformation which is controlled by the cooling rate. During L-DED this transformation is hardly accomplished, commonly calling for a post-build heat treatment. For the first time, an intrinsic laser-based heat treatment was applied to promote this phase transformation in the Additively Manufactured HEA in a layer by layer approach. Process parameters for the intrinsic heat treatment were varied and investigated in terms of temperature–time cycles, cooling rates and penetration depth. The microstructure of as-built and differently heat-treated samples was investigated. In the as-built condition, the duplex structure consist mainly of ordered and disordered bcc phase and a small fraction of thin fcc-plates (40%). It was found that the fcc phase fraction can be significantly increased up to 58% by applying an intrinsic heat treatment. The heat treatment involves nucleation of new fcc plates as well as thickening of the existing plates. The process-related inhomogeneity of the microstructure resulting from heat affected zones at melt pool boundaries is not eliminated due to the short interaction times. In contrast to the conventional post-process heat treatment at 900 °C for 6 h, the microhardness is not significantly reduced during intrinsic heat treatment and remains in the range of 400 HV0.3. Intrinsic heat treatment is however beneficial, since it can be applied selectively. Thus, it offers novel possibilities for surface cladding applications.Graphical

Near-threshold fatigue crack growth in laser powder bed fusion produced alloy 718

The role of microstructure in influencing fatigue crack growth behavior for laser powder bed fusion (LPBF) produced nickel superalloy 718 was examined. Two common post-build heat treatments were applied to produce two distinct microstructures, one which retained much of the solidification structure from additive manufacturing, while the other was mostly recrystallized. For both groups, residual stresses were assessed along the crack path by neutron diffraction. At low load ratios (R = 0.1), the non-recrystallized LPBF material had the lowest and most varied fatigue crack growth thresholds at 6–7.2 MPa m1/2. This is attributed to a reduction in crack path roughness induced crack closure and high superimposed residual stresses. The recrystallizing heat treatment coarsened and homogenized the grain structure substantially, thus increasing the threshold to 7.3–7.6 MPa m1/2 due to a substantially rougher crack path and completely relieved residual stresses. Both LPBF heat treatments showed negligible effect of build orientation and gave significantly lower fatigue thresholds compared to wrought material tested in the L-T orientation (∼11 MPa m1/2). At high load ratios, the difference in fatigue behavior between microstructures was reduced but still present and was attributed to differences in geometric shielding from crack path roughness, grain size, and degree of microstructural homogeneity.

Bonding integrity of hybrid 18Ni300-17-4 PH steel using the laser powder bed fusion process for the fabrication of plastic injection mould inserts

Laser powder bed fusion (LPBF) is a metal additive manufacturing (AM) process for fabricating high-performance functional parts and tools in various metallic alloys, such as titanium, aluminium and tool steels. One specific AM application is fabricating conformal cooling channels (CCC) in plastic injection moulding tool inserts to improve cooling efficiency. This article reports the development of a novel hybrid powder-wrought alloy steel combination intended for injection mould inserts use. In this investigation, cylindrical parts made of 18Ni300 steel powder and wrought 17-4 PH steel were additively fabricated using a hybrid-build LPBF AM technique, followed by various post-build heat treatments. Standard mechanical and microstructural techniques were employed to examine the bonded powder-substrate interface. Microstructure analysis revealed defect-free, fully dense, homogenous powder-substrate fusion across a 280-µm-thick region. Tensile tests confirmed strong powder-substrate bonding due to solid solution strengthening within the region. All tensile fractures were ductile under all heat treatment conditions and occurred about 8 mm from the interface, at the side where the materials were of lower strength. The hybrid-built parts exhibited an ultimate tensile strength of 1009–1329 MPa, with 16.1–17.4% elongation at fracture. Hardness values on the AM-deposited and substrate sides were 31–55 HRC and 32–43 HRC, respectively. A direct post-build 490 °C/1 h age-hardening treatment achieved the best combination of hardness, tensile strength and ductility. The overall result demonstrates that hybrid-built powder 18Ni300-wrought 17-4 PH steel can be a material choice for manufacturing durable and high-performance injection mould inserts for high-volume production.

Microchemical evolution of irradiated additive-manufactured HT9

The microstructural responses under 5 MeV Fe2+ single-ion-beam irradiation of three conditions of additive-manufactured (AM) HT9 steel using a powder-based directed energy deposition (DED) technique with and without postbuild heat treatments were investigated. Besides the observed dislocation loop formation and the absence of cavities at the irradiation condition of 50 dpa at 460 °C, Ni/Si/Mn-rich precipitates are found to form in all three conditions of AM-HT9, whereas Cu-rich clusters that arise from Cu uptake from the DED process are only observed in the heat-treated conditions, and not in the as-built (ASB) condition. Coprecipitation of the Cu- and Ni/Si/Mn-rich clusters occur near defect sinks such as line dislocations and grain boundaries in the heat-treated AM-HT9. The variation in microchemical evolution can be directly linked to the starting sink strength of the 3 AM-HT9 conditions, and the ASB condition with higher sink strength suppressed the responses observed in the postbuild heat-treated specimens.

Effect of heat treatment on creep behavior of 316 L stainless steel manufactured by laser powder bed fusion

The objective of this study is to understand the thermal stability of microstructure and its effect on the creep behavior of additively-manufactured 316L stainless steel (AM 316L SS). Creep specimens were fabricated from rods printed by a laser powder bed fusion process. Six different heat treatments, namely 650 °C/1 h, 700 °C/1 h, 750 °C/1 h, 800 °C/1 h, 900 °C/1 h and 1050 °C/1 h were applied to the creep specimens. The heat-treated specimens were creep-tested under the same condition, 550 °C/275 MPa to evaluate the effect of post-build heat treatment on the creep behavior of AM 316L SS. In the temperature range of 650–750 °C, dislocation density within cells, and cell size and wall thickness were affected by the heat treatment, while elemental segregation at boundaries remained unchanged and Mn-enriched Si oxide particles remained stable. In the temperature range of 750–900 °C, concurrent changes were observed in dislocation cell structures, elemental segregation and oxide particles. The 1050 °C-heat treatment removed cell structures and boundary solute segregations, leading to formation of equiaxed grains; Mn-enriched Si oxide particles in the as-built specimen were replaced by more stable Mn-enriched Cr oxides. The creep life of AM 316L SS increased after the heat treatment at 650 °C and then decreased with increasing temperature up to 900 °C where cell/subgrain structures still existed. The creep rate and creep elongation followed an opposite trend. The creep rate can be correlated with the structural parameters of cell/subgrain size and cell wall/boundary thickness and can be rationalized by different strengthening mechanisms of dislocation cells and subgrains. The heat treatment affected strongly the primary and secondary creep but had a minimal effect on the tertiary creep of AM 316L SS.

Evolution of the Microstructure of Laser Powder Bed Fusion Ti-6Al-4V During Post-Build Heat Treatment

The microstructure of additively manufactured Ti-6Al-4V (Ti64) produced by a laser powder bed fusion process was studied during post-build heat treatments between 1043 K (770 °C) and just above the β transus temperature 1241 K (1008 °C) in situ using high-energy X-ray diffraction. Parallel studies on traditionally manufactured wrought and annealed Ti64 were completed as a baseline comparison. The initial and final grain structures were characterized using electron backscatter diffraction. Likewise, the initial texture, dislocation density, and final texture were determined with X-ray diffraction. The evolution of the microstructure, including the phase evolution, internal stress, qualitative dislocation density, and vanadium distribution between the constituent phases were monitored with in situ X-ray diffraction. The as-built powder bed fusion material was single-phase hexagonal close packed (to the measurement resolution) with a fine acicular grain structure and exhibited a high dislocation density and intergranular residual stress. Recovery of the high dislocation density and annealing of the internal stress were observed to initiate concurrently at a relatively low temperature of 770 K (497 °C). Transformation to the β phase initiated at roughly 913 K (640 °C), after recovery had occurred. These results are meant to be used to design post-build heat treatments resulting in specified microstructures and properties.

Monitoring residual strain relaxation and preferred grain orientation of additively manufactured Inconel 625 by in-situ neutron imaging

Microstructures produced by Additive Manufacturing (AM) techniques determine many characteristics of components produced by this particular manufacturing technique. Residual stress and texture are among those characteristics, which need to be optimized to meet dimensional and strength requirements. Post-build heat treatments are necessary to relief residual stresses, homogenize the microstructure and to develop the necessary microstructures (precipitation or solution hardening) for strength. Our focus in this study is the measurement of residual stresses during a vacuum stress relief (VSR) heat treatment. We employ the energy-resolved neutron imaging to investigate, in-situ, the uniformity of the as-built texture and to map the residual strain distributions within samples of Inconel 625 (IN625). The samples used in this study were printed using the powder-bed metal laser melting additive manufacturing technique. Strain and texture variations were measured at room temperature for the as-built samples as well as their changes during stress relief annealing at 700 °C and 875 °C in a vacuum furnace. The uniformity of crystalline plane distribution, from which texture can be inferred, was imaged with sub-mm spatial resolution for the entire sample area exceeding several square centimeters. Despite the limited accuracy of in-situ lattice strain reconstruction during sample annealing, the results indicate that most of the strain relaxation occurs at 700 °C within the first 2–3 h. Relaxation of the strain at 875 °C happened at a much faster rate. In addition, energy-resolved neutron imaging demonstrates the possibility to correlate the uniformity of grain orientation and the degree of texture variations with printing parameters, in particular the laser translation speed. Simulations of the AM build process were carried out to predict the residual stress distributions within the samples as a function of the build process parameters. Comparisons of the simulation results to the room temperature experimental measurements show good agreements when the simulation data are averaged over the volume of the part confirming the usefulness of the experiments for validating simulation results. The neutron imaging technique described in this study can be helpful for the evaluation of bulk crystallographic characteristics in AM printed materials and can be used as a guide for developing the heat treatment cycle and for validations of VSR simulation results.

Breaking bad: towards certifiable additively manufactured alloys using post-build heat treatment

Breaking bad: towards certifiable additively manufactured alloys using post-build heat treatment