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The individual effects of strain rate and temperature on the strain hardening rate of a quenched and partitioned steel have been examined. During quasistatic tests, resistive heating was used to simulate the deformation-induced heating that occurs during high-strain-rate deformation, while the deformation-induced martensitic transformation was tracked by a combination of x-ray and electron backscatter diffraction. Unique work hardening rates under various thermal–mechanical conditions are discussed, based on the balance between the concurrent dislocation slip and transformation-induced plasticity deformation mechanisms. The diffraction and strain hardening data suggest that the imposed strain rate and temperature exhibited dissonant influences on the martensitic phase transformation. Increasing the strain rate appeared to enhance the martensitic transformation, while increasing the temperature suppressed the martensitic transformation.

The microstructures and hardnesses of Co–10Al–9W–1C, Co–7Al–5W–1C, and Co–7Al–5W (at. pct) alloys are reported. Homogenization of the Co–10Al–9W–1C alloy was unsuccessful at 1300 °C and both B2–CoAl and η carbide phases remained in the interdendritic regions. However, the lower-solute Co–7Al–5W–1C and Co–7Al–5W alloys did homogenize at 1300 °C. Upon aging the Co–10Al–9W–1C alloy at 800 °C, the undissolved η carbide transformed into W-supersaturated D019–Co3W phase and subsequently into γ′-Co3(Al,W) phase, indicating the stability of the γ′ phase in the C-doped alloy in contrast with ternary Co–Al–W alloys where the γ′ is metastable. Also, high γ′ volume fractions and low γ′ coarsening rates were revealed by transmission electron microscopy in the various Co–Al–W–C alloys. These observations are explained by the effects of C on the phase equilibria and the γ/γ′ composition in the Co–Al–W system. Finally, the microhardness is increased while the density is decreased by alloying with C, which could result in higher specific strengths in the C-doped alloys.

Electron microscopy revealed continuous and discontinuous precipitation of κ-Co3AlC0.5 in a Co-10Al-3Cu-1C (at. pct) alloy during aging at 500 °C, 850 °C, and 900 °C. The kinetics of the discontinuous reaction at 500 °C are sluggish. Increasing the temperature increases the kinetics significantly, due to the exponential increase in the Al grain boundary diffusivity. However, the kinetics at 900 °C are slower than those at 850 °C, due to a significant decrease in the driving force.

High-energy, microfocus x-ray imaging, or x-radiography, is a useful tool for in situ analysis and monitoring of materials processing. Large fields-of-view, spatial and temporal resolutions sufficient for mesoscopic imaging, and high-energy x-rays capable of probing metallic alloy samples make the technique attractive for in situ solidification studies in the laboratory. Here, we demonstrate the usefulness of high-energy, microfocus x-radiography in the laboratory, particularly when paired with complementary techniques. Multimodal, multiscale characterization was performed, including x-radiographic analysis of solidifying Al-Ag and compositional analysis of the same sample after solidification with scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). The dynamics observed through x-radiography during solidification are compared to the compositional results obtained by EDS. The fraction solid measured in radiographs is also used in combination with a calculation of phase diagrams (CalPhaD) Scheil solidification simulation to reconstruct a spatiotemporal microsegregation map. The multimodal, multiscale characterization techniques presented here illustrate a promising pathway toward improved analyses and monitoring of materials processing within a laboratory setting.

This work presents a detailed instructional demonstration using the Rietveld refinement software MAUD for evaluating the crystallographic texture of single- and dual-phase materials, as applied to High-Pressure-Preferred-Orientation (HIPPO) neutron diffraction data obtained at Los Alamos National Laboratory (LANL) and electron backscatter diffraction (EBSD) pole figures on Ti–6Al–4V produced by additive manufacturing. This work addresses a number of hidden challenges intrinsic to Rietveld refinement and operation of the software to improve users’ experiences when using MAUD. A systematic evaluation of each step in the MAUD refinement process is described, focusing on devising a consistent refinement process for any version of MAUD and any material system, while also calling out required updates to previously developed processes. A number of possible issues users may encounter are documented and explained, along with a multilayered assessment for validating when a MAUD refinement procedure is finished for any dataset. A brief discussion on appropriate sample symmetries is also included to highlight possible oversimplifications of the texture data extracted from MAUD. Included in the appendix of this work are two systematic walkthroughs applying the process described. Files for these walkthroughs can be found at the data repository located at: https://doi.org/10.18434/mds2-2400 .

CrCoNi multi-principal element alloys (MPEAs) have shown good strength-ductility combinations, but few other mechanical properties have been evaluated in these alloys so far. Although optimal wear-resistant alloys depend upon the intended application, a hard and tough material is often desirable. In this work, as-cast Cr40Co40Ni20 was tested for wear under dry-sliding conditions against an alumina pin, exhibiting good wear resistance and low coefficient of friction (CoF) of 0.12. To further improve the wear behavior, carbon (C) additions were evaluated in this alloy and in Cr40Co30Ni30, up to the liquid solubility limit at 1600 °C (~24 at. pct C). Alloy design was performed using computational thermodynamic calculations. Predicted microstructures contain: self-lubricating graphite flakes, hard primary Cr-rich carbides, and a tough eutectic matrix; in good agreement with experimental results. As-cast Cr40Co40Ni20-C, even without microstructural refinement, displayed low specific wear rate (on the order of 10−4 mm3/Nm) and moderate CoF (0.55-0.62). Its performance was hampered by the fracture and detachment of coarse primary carbides, which introduced an additional abrasive element into the tribosystem. These findings indicate that C additions to CrCoNi alloys, along with the refinement of primary carbides, represent a promising strategy to further improve the wear performance of MPEAs.

The nanostructured ferritic alloy 14YWT is a promising candidate for in-core use in generation IV nuclear reactors, due to a dense dispersion of insoluble, ultrafine-scale Y-Ti-O nano-oxides, which provide a high degree of irradiation tolerance and thermal stability. This study investigates the effects of heat treatment on the workability of 14YWT, along with the effect of processing history on abnormal grain structures and radial microstructural uniformity. In this study, a 14YWT rod consolidated at 850 °C was heat treated in argon at 1100 °C, 1150 °C, 1200 °C, or 1250 °C for 1 or 8 hours and changes in mechanical properties and microstructure were examined using microhardness and electron backscattered diffraction (EBSD). Two distinct types of large abnormal grains were observed, each with unique processing origins, including one with high and the other with low strain energy. Consolidation via direct extrusion resulted in radial microstructural gradients, where the center of the rod was softer with larger grain sizes and lower strain energies. These gradients persisted and intensified throughout heat treatment. Based upon this work, the recommended heat treatment for increased workability with minimal microstructural change is 1150 °C for 1 hours.

A thermodynamic model, based on SimuSage, was developed to simulate refractory corrosion between a magnesia-based refractory material and ferronickel (FeNi) slags. The model considers a theoretical cross-section of a refractory material to simulate a ferronickel smelter application. The current model is structured into 10 zones, which characterize different sectors in the brick (hot to cold side) perpendicular to the refractory surface with an underlying temperature gradient. In each zone, the model calculates the equilibrium between the slag and a specified amount of refractory material. The emerging liquid phases are transferred to subsequent zones. Meanwhile, all solids remain in the calculated zone. This computational process repeats until a steady state is reached in each zone. The simulation results show that when FeNi slag infiltrates into the refractory material, the melt dissolves the magnesia-based refractory and forms silicates (Mg,Fe,Ca)2SiO4 and Al spinel ((Mg,Fe)Al2O4). Furthermore, it was observed that iron oxide from the slag reacts with the refractory and generates magnesiowustite (Mg,Fe)O. Practical lab-scale tests and scanning electron microscopy (SEM)/Energy Dispersive X-ray Spectroscopy (EDS) characterization confirmed the formation of these minerals. Finally, the refractory corrosion model (RCM) ultimately provides a pathway for improving refractory lifetimes and performance.

Due to their high strength, formability and affordable cost, quenched and partitioned (Q&P) steels have shown the potential to reduce the mass of vehicles, thereby decreasing fuel consumption during service. Furthermore, because a lower mass of steel is used in each vehicle, energy consumption associated with the steelmaking process is also reduced. Q&P steels utilize the deformation-induced martensitic transformation (DIMT) of metastable retained austenite to enhance ductility and strain hardening. Accordingly, improvement of mechanical performance is contingent on the ability to precisely control the chemical and mechanical stability of austenite. Considering the multitude of factors that influence austenite stability, optimizing microstructures to delay necking or fracture is challenging, particularly as temperature and strain rate increase. Tensile tests of an intercritically annealed C-Mn-Si Q&P steel were performed over a range of strain rates (10−4 to 10−1 s−1) to evaluate effects on the DIMT and sheet tensile properties. As strain rates increased from 10−4 to 10−1 s−1, the uniform elongation decreased from approximately 19 to 14 pct. This reduction in uniform elongation is associated with a decrease in the strain hardening exponent near the onset of strain localization. Based on experimental data from this study and review of previous research, it is postulated that the strengthening contribution of DIMT is controlled by competing effects of: (i) a decreasing chemical driving force for DIMT caused by deformation-induced heat accumulation at higher strain rates and (ii) an increasing number of martensite nucleation sites. This suggests that tailoring austenite stability for specific deformation conditions could enable further optimization of formability and vehicle crash behavior.

Medium carbon steels alloyed with two levels each of V and Si were heat treated to form tempered martensite and bainite, followed by nitriding to evaluate their effects on case hardness and residual stress. Microstructures were quantitatively characterized with Vickers microhardness testing, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), conventional transmission electron microscopy (CTEM), and scanning transmission electron microscopy (STEM). Measurements of subgrain size, cementite size, dislocation density, and volume fractions of nitride precipitates were combined in a strength model to predict the contributions of V and Si to maximum case hardness after nitriding. Higher V contents lead to increases in maximum case hardness by increasing the volume fraction of MX precipitates. Increases in Si content lead to increased maximum case hardness by increasing the volume fraction of amorphous (Si and Mn)-containing nitride precipitates; the presence of Mn in these precipitates has not been previously reported. Higher Si contents also lead to increases in solid solution strengthening because the majority of Si remains in solution in the ferrite matrix. Greater volume fractions of MX and (Si and Mn)-containing nitrides both lead to higher magnitudes of compressive residual stress. The results presented here demonstrate that alloying can improve the properties after nitriding, providing insight into advanced nitriding steel grades and potentially enabling a wider range of steel microstructures to be nitrided without a debit in performance.

Solidification processing offers the first opportunity to control microstructure, properties, and performance in metallic alloy components. Until recently, microstructural evaluations were limited to post-solidification characterization by destructive methods. We review the development of time-resolved, in situ imaging techniques capable of capturing solid–liquid interfacial evolution in metallic alloys with high spatial and temporal resolution under diverse solidification conditions relevant for applications ranging from conventional directional solidification, crystal growth, and casting, to welding and additive manufacturing. These experiments enable direct visualization of transient behaviors that would otherwise remain unknown, uniquely providing insights into the physics that impact microstructure and defect development, and strategies for microstructural control and defect mitigation. Understanding microstructural evolution and the characteristics that form under various solidification conditions is essential for the development of multiscale, experimentally informed predictive modeling. This is highlighted by solidification simulations that utilize in situ measurements of solidification dynamics from state-of-the-art experimental techniques.

The field of solidification has evolved from metallurgical alchemy to a predictive science over the past century. Our particular focus is on metals and their alloys, whose thermophysical properties tend to differ distinctively from that of organic systems. Rapid advances in modeling efforts and real-time experiments have yielded a wealth of new and quantitative information across relevant length- and time scales, thereby expanding our understanding of the liquid-to-solid phase transition. The articles in this issue highlight some important recent developments in the field, including solidification at extreme rates, as well as the state-of-the-art computational and experimental techniques that allow us to probe the otherwise improbable. In light of this progress, we identify critical issues and open questions that point to future research directions in solidification science.

Additive manufacturing (AM) promises a major transformation for manufacturing of metallic components for aerospace, medical, nuclear, and energy applications. This perspective paper addresses some of the opportunities for alloy and feedstock design to achieve site-specific and enhanced properties not attainable by conventional manufacturing processes. This paper provides a brief overview of the role of powders, as well as solidification and solid-state phase transformation phenomena typically encountered during fusion-based AM. Three case studies are discussed that leverage the above to arrive at microstructure control. The first case study focuses on approaches to modify the solidification characteristics by in-situ alloying. The second case study focuses on the need for concurrent design of alloys and processing conditions to arrive at the columnar to equiaxed transition during solidification. The third case study focuses on the design of a cobalt alloy for AM, with emphasis on tailoring liquid and solid state phase transformations. The need for comprehensive knowledge of processing conditions during AM, in-situ and ex-situ probing of microstructure development under AM conditions, and post-print processing, characterization, and qualification are articulated for the design of future alloys and component geometries built by AM.

Steels are ubiquitous due to their affordability and the landscape of useful properties that can be generated for engineering applications. But to further expand the performance envelope, one must be able to understand and control microstructure development by alloying and processing. Here we use multiscale, advanced characterization to better understand the structural and chemical evolution of AISI 4340 steel after quenching and tempering (Q&T), including the role of quench rate and short-time, isothermal tempering below 573 K (300 °C), with an emphasis on carbide formation. We compare the microstructure and/or property changes produced by conventional tempering to those produced by higher temperature, short-time “rapid” tempering. We underscore that no single characterization technique can fully capture the subtle microstructure changes like carbon redistribution, transition carbide and/or cementite formation, and retained austenite decomposition that occur during Q&T. Only the use of multiple techniques begins to unravel these complexities. After controlled fast or slow quenching, η transition carbides clearly exist in the microstructure, likely associated with autotempering of this high martensite start temperature (Ms) steel. Isothermal tempering below 598 K (325 °C) results in the relief of carbon supersaturation in the martensite, primarily by the formation of η transition carbides that exhibit a range of carbon levels, seemingly without substitutional element partitioning between the carbide and matrix phases. Hagg transition carbide is present between 300 °C and 325 °C. After conventional tempering at or above 598 K (325 °C) for 2 h, cementite is predominant, but small amounts of cementite are also present in other conditions, even after quenching. Previous work has indicated that silicon (Si) and substitutional elements partition between the cementite, which initially forms under paraequilibrium conditions, and the matrix. Phosphorous (P) may also be preferentially located at cementite/matrix interfaces after high temperature tempering. Slower quench rates result in greater amounts of retained austenite compared to those after fast quenching, which we attribute to increased austenite stability resulting from “autopartitioning”. Rapid, high temperature tempering is also found to diminish tempered martensite embrittlement (TME) believed to be associated with the extent of austenite decomposition, resulting in mechanical properties not attainable by conventional tempering, which may have important implications with respect to industrial heat treatment processes like induction tempering. Controlling the amount and stability of retained austenite is not only relevant to the properties of Q&T steels, but also next-generation advanced high strength steels (AHSS) with austenite/martensite mixtures.

Accumulative roll bonding (ARB) of aluminum alloy strips is often limited by severe edge cracking due to large, single-pass rolling reductions. Edge cracks are often caused by either poor alignment of the roll-bonded strips or lateral spreading. This work shows that lateral spreading can be reduced significantly by roll-bonding strips of interest within a frame of sacrificial material. For the conditions tested, it has been found that frames with 6.3 mm of constraint width are optimal in reducing edge cracking and maintaining thickness homogeneity during ARB. This methodology was found to greatly improve sample quality and yield when applied to multiple ARB cycles.

Rapid tempering involves shorter times and faster heating rates compared to conventional tempering. Utilizing rapid tempering via industrial processes, such as induction heating, not only offers the opportunity for improved mechanical properties, but also for reduced processing times and energy costs. The current study demonstrates an improvement in toughness with rapid tempering by examining impact toughness at a constant tempering parameter for short-time (1 s) and conventional (3600 s) tempering treatments of 4340 steel. Fracture behavior is found to complement the observed toughness behavior, where higher impact energy conditions are associated with a greater percentage of ductile fracture. The role of the Hollomon–Jaffe tempering parameter, as well as the use of hardness as a metric to characterize degree of tempering, is discussed in light of the results comparing rapid and conventional tempering conditions. This study indicates promising mechanical properties associated with short-time tempering, especially within the tempered martensite embrittlement (TME) regime, and exposes challenges associated with predicting performance strictly based on hardness when rapid tempering is utilized.

Uranium-6 wt pct niobium (14 at pct niobium) displays the shape memory effect (SME), where deformation proceeds by twinning and twin rearrangement via boundary migration within the SME regime. In-situ neutron diffraction during deformation suggests that after SME strain is exhausted, deformation proceeds via another twinning mechanism that does not recover to the original parent orientation upon reheating and transformation. Here we show from in-situ tensile and compressive loading and unloading experiments that early post-SME twins partially reverse during unloading, which is evident by rapid texture evolution, and this reversion is responsible for the inelastic portion of the previously reported ~ 2 pct strain recovery.

We introduce a new phase-field formulation of rapid alloy solidification that quantitatively incorporates nonequilibrium effects at the solid-liquid interface over a very wide range of interface velocities. Simulations identify a new dynamical instability of dendrite tip growth driven by solute trapping at velocities approaching the absolute stability limit. They also reproduce the formation of the widely observed banded microstructures, revealing how this instability triggers transitions between dendritic and microsegregation-free solidification. Predicted band spacings agree quantitatively with observations in rapidly solidified Al-Cu thin films.

The influence of W content on the Co(W)Zn system and the behavior of individual elements was investigated. Cobalt is a so-called critical element and is one of the main parts in hard metal products. Because of its toxicity, it requires special care in handling. Further optimization of hard metal recycling, especially by the zinc process, is needed to use scrap as a secondary resource. In this work, Co(W) materials were put in contact with liquid zinc and held at specific temperatures, giving insight into the formation of intermetallic Co-Zn phases by varying the temperature, duration, and W content. Lower temperatures led to a minimum layer width, and increasing temperatures and W contents resulted in greater thicknesses of the intermetallic phases. The element distribution analyses show that W diffuses from the base material through the intermetallic Co-Zn layer and accumulates at detached Co-Zn phases, forming thin, enriched filaments. This can be attributed to the fact that the intermetallic Co-Zn phases and Zn have no solubility in W. Consequently, the latter is located on the outside of these phases. The combination of practical experiments and statistical analyses will ultimately provide a possibility for improving recycling processes.

The Co55Cr40Ni5 multicomponent alloy was designed to be single-phase face centered cubic (FCC), display high strength, and have the ability to undergo transformation-induced plasticity (TRIP) during plastic deformation. The alloy was produced, and phase stability was monitored in-situ by synchrotron X-ray diffraction during thermomechanical deformation to observe the formation and evolution of the hexagonal close packed (HCP) martensite phase as a function of applied stress. The alloy displays a good combination of strength and ductility, owing largely to the TRIP effect, which increases the strain hardening rate during deformation.

Metal additive manufacturing (AM) enables customizable, on-demand parts, allowing for new designs and improved engineering performance. Yet, the ability to control AM metal alloy microstructures (i.e., grain morphology, crystallographic texture, and phase content) is lacking. This work performs corroborative neutron diffraction and large-scale electron backscatter diffraction (EBSD) measurements to assess crystallographic texture in electron beam melted (EBM) Ti-6Al-4V as a function of scan strategy and build height. Texture components for one raster and two spot melt scan strategies were evaluated using a triclinic specimen symmetry to capture all possible texture components, which were found to be considerably different than previously reported values from studies employing orthotropic specimen symmetry. This finding highlights the importance of a standard method and best practice for assessing textures produced by AM. Texture was found to vary between scan strategies, but changed minimally as a function of build height. Parent phase β-Ti reconstructions obtained from as-built crystallographic orientations revealed spot melt scan strategies produced finer equiaxed/columnar grains with clear { 001 } β build direction fiber textures, whereas the raster scan strategy produced large columnar grains and a weaker { 001 } β build direction fiber texture. The observed grain morphologies agree with those predicted by solidification theory for the thermal gradients and solidification velocities experienced during the build process. The presence of a strong { 001 } β fiber orientation (typical of cubic solidification) produced by spot melting was found to correlate with a previously unreported { 01 1 2 } α fiber texture in the as-built condition and colony microstructures. The { 01 1 2 } α fiber texture was weakly observed for the raster scan strategy, and { 001 } β oriented grains preferentially transformed into α ′ martensite with orientations between { 1 1 00 } α and { 11 2 0 } α . This shift in product α -Ti orientations has not yet been reported, and further work is recommended to understand these crystallographic signatures in the context of solid-state phase transformations. The presence of the { 01 1 2 } α fiber texture is proposed as a useful diagnostic for evaluating the solidification or transformed microstructure condition (e.g., grain morphology and texture) of Ti-6Al-4V AM builds via accessible techniques like laboratory X-ray diffraction.

Tempered martensite embrittlement (TME) is investigated in two medium carbon, high strength steels, 4340 (low silicon) and 300-M (high silicon), via rapid (1, 10, or 100 s) and conventional (3600 s) tempering. Rapid tempering of 4340 diminishes the depth of the TME toughness trough, where improvements in impact toughness correspond to the suppression of retained austenite decomposition. In 300-M, retained austenite decomposition is suppressed to an even greater extent by rapid tempering. While toughness improves overall after rapid tempering, TME severity remains consistent in 300-M across the tempering conditions examined. Through interrupted tensile tests, it was found that the 300-M conditions that exhibit TME are associated with mechanically unstable retained austenite. Unstable retained austenite is shown to mechanically transform early in the deformation process, presumably resulting in fresh martensite adjacent to interlath cementite that ultimately contributes to TME. The present results emphasize the role of both the thermal decomposition and mechanical transformation of retained austenite in the manifestation of TME.

Medium and high entropy alloys (MEAs/HEAs), which typically have three or more main elements, were initially designed to have high configurational entropy (Sconf) stabilizing a simple, single-phase solid solution (SS) over multi-phase alloys. Having multiple main elements will indeed increase the Sconf of simple SSs, but it may decrease the enthalpy also increase, in a lower degree, Sconf of other complex phases, leading to multi-phase microstructures. Therefore, although the initial idea behind MEAs/HEAs was refuted, the interest remains, the focus shifted to exploring its vast compositional field, which includes an almost infinite number of alloys. Some of them with potentially better properties than those existing today. The Cantor alloy (equiatomic CrMnFeCoNi) and the equiatomic CrCoNi alloy, both single-phase with face-centered cubic (FCC) structure, are among the toughest materials ever reported. In this work, computational thermodynamic calculations (CALPHAD method) predicted that C additions in the Cr40Co40Ni20 MEA favor the formation of a promising multi-phase microstructure for wear applications. A large amount of C was incorporated into the alloy by melting in a graphite crucible, this process allowed C saturation in the melt, which as will be shown, can be well controlled by carefully selecting the casting temperature, in this case we achieved 24 at% C by melting at 1600 oC. A Cr30.4Co30.4Ni15.2C24 MEA was produced, characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS). Experimental results revealed a microstructure composed of: graphite flakes, hard primary Cr-rich carbides, and a tough eutectic matrix of FCC phase and carbides; in good agreement with thermodynamic calculations. These findings highlight the great flexibility and potential in MEAs/HEAs design, making it possible to obtain microstructures and sets of properties that are beneficial for a given application.

Changes in the microstructure and mechanical properties of Cu-Ti alloy sheets during cold rolling and subsequent annealing were studied with and without Cu-Ti precipitates in the initial microstructures. Pre-existing Cu-Ti precipitates plastically deformed and severely elongated in the rolling direction via cold rolling, accelerating the formation of a nano-lamellar structure. A mean lamellar boundary spacing of 20 nm was achieved at an equivalent strain of 6.7. Vickers hardness increased with decreasing lamellar boundary spacing. Subsequent annealing after cold rolling clearly enhanced the mechanical properties, and a maximum Vickers hardness value of 443 HV (4.35 GPa) was attained in the sample with pre-existing precipitates strained to 6.7. These results suggest that pre-existing precipitates promote microstructural refinement during heavy cold rolling, and that heavily cold-rolled Cu-Ti alloys exhibit anneal hardening behavior, leading to excellent mechanical properties.

Quenching and partitioning (Q&P), a new heat treatment concept to develop high-strength martensitic microstructures with retained austenite (RA), has been implemented industrially to make sheet products. This process is also of interest for thicker plate products, to employ transformation-induced plasticity to enhance toughness and/or wear resistance. The applicability of the Q&P process to plate steel is explored considering through-thickness thermal profiles and associated microstructural gradients. Design methodologies are developed for both the quenching and the partitioning steps of plate processing, coupling thermal models with microstructural design concepts. The design methodologies are experimentally validated using a 0.4 wt pct C 300 M alloy through dilatometry simulations of plate Q&P processing, according to numerically simulated profiles. Q&P microstructures were successfully obtained through the thickness of a simulated 18-mm plate, and attractive RA fractions were achieved.

Compression stress-strain curves of a number of refractory high entropy alloys (RHEAs) were generated at temperatures ranging from room temperature to 1000 °C. It is shown that solid-solution strengthening in these alloys has both an athermal and a thermal component. Results from mechanical testing are combined with literature data to develop solid-solution strengthening models for both components that incorporate the particularities of single-phase body centered cubic (BCC) materials. The athermal component is affected by a combination of atomic size mismatch and elastic modulus mismatch, which depend upon average values from each alloy, thereby allowing this component to be estimated in a high-throughput fashion. On the other hand, the thermally-activated yield stress component does not correlate with any parameter that can be calculated by averaging pure elemental atomic properties and it is observed to be larger than the values found for pure BCC refractory metals and their dilute alloys. Overall, RHEAs are found to have larger thermal and athermal yield stress components compared to pure or conventional refractory alloys, which explains their relatively high strengths at room temperature.

While tempering reactions under furnace conditions have been extensively studied, short-time tempering at higher temperatures, as might apply to induction tempering, has not been thoroughly explored. The mechanical behavior and phase development of short-time (1, 10, and 100 seconds) and conventionally (3600 seconds) tempered 4340 steel are compared at an equivalent degree of tempering defined by the Hollomon–Jaffe tempering parameter. The tempering parameter accurately predicts hardness values across short-time and conventional tempering conditions, but is less able to describe phase evolution associated with short-time tempering. Room temperature Charpy impact toughness and ductile-to-brittle transition temperature systematically improve with shorter tempering times at an equivalent tempering parameter. In particular, rapid tempering significantly increases toughness within the tempered martensite embrittlement regime. Relative to conventional tempering, shorter tempering times exhibit higher retained austenite content for a given tempering parameter, although no systematic or significant difference in cementite or transition carbide content is observed between time conditions. The retained austenite decomposition behavior indicates that the relationship between the classical tempering stages is altered at short tempering times, where increased overlap and/or “re-ordering” of stage II and III tempering are observed.

Two low-carbon 9-Cr ferritic-martensitic steels were designed with the aim of decreasing M23C6 and maintaining or increasing MX phase fraction. A low-carbon (LC) alloy and a low-carbon, zero-niobium (0Nb) alloy were fabricated, their designs based upon the P92 alloy system. Solutionizing temperatures to maximize V and Nb in solution while avoiding δ-ferrite were determined to be 1170 °C for the P92 alloy and 1050 °C for LC and 0Nb, significantly lower than predicted using ThermoCalc® modeling. As was intended, the M23C6 phase fraction was reduced for LC and 0Nb alloys after both heat treating and aging relative to the base P92 alloy, as determined by wide angle x-ray scattering (WAXS) analysis. Dislocation density measurements from x-ray line broadening in P92 and LC suggest these alloys had more stable dislocation substructures than 0Nb at lower temperature and shorter time aging conditions. While LC exhibited lower microhardness than P92 at room temperature, the tensile properties were comparable at 650 °C, suggesting that elevated temperature strength can be achieved with lower carbon contents. Aging studies showed that P92 had a more stable microstructure for higher temperature and longer time aging conditions. The P92 alloy also had a longer stress rupture life, implying that the M23C6 precipitate contribution to thermal stability is important. Evidence of Z-phase was discovered for the LC alloy aged 10,000 h at 650 °C, corresponding to decreased strength and increased ductility. Overall, the stress rupture lives of the modified heat-treatment variations of P92 and LC compare favorably to literature values for 9% Cr steels with conventional heat treatments.

While some high entropy alloys (HEAs) have been shown to display remarkable combinations of properties, exploration of the extensive multicomponent space by conventional methods is experimentally intractable. Thus, identifying and developing high-throughput screening methods is paramount to alloy design. Here, an experimental methodology is developed for rapid yield strength estimations of single-phase HEAs, which involves the production and testing of a compositionally-graded sample made by a diffusion-multiple approach. The sample is analyzed by a combination of nanoindentation and microstructural characterization, where the nanohardness results are analyzed by different conversion equations to determine yield strength. The values estimated by nanohardness agree with bulk tensile properties for a total of 8 compositions. Both are compared to a solid solution strengthening model, again yielding a good correlation. The experimental and simulation results indicate that, in this system, the strength is maximized when the atomic size mismatch is maximized. Furthermore, it is necessary to consider the strain hardening of these alloys to accurately estimate their strength by nanoindentation. A pathway is presented here. This work shows that high-throughput methodologies for predicting and measuring properties are promising for designing new HEAs with desirable combinations of properties.

Variant selection of Ni2(Mo,Cr) precipitates (γ′) in a low coefficient of thermal expansion Ni-Mo-Cr-W alloy has been investigated as a function of precipitate size and applied stress. The lenticular-shaped, coherent γ′ precipitates form with a {110}M/(010)p habit plane. During conventional aging, all 6 variants of the Ni2(Mo,Cr) precipitates form and coarsen with aging time. With the application of external loading below the yield stress during aging, variants with {110}M habit planes that experience the largest dilations resulting from the externally applied stress are favored. Phase field modeling, coupled with elasticity theory, has been employed to simulate the development of variant selection of γ′ precipitates with and without applied external loading. Similar to the experimental results, the γ′ precipitates tend to form parallel to each other during coarsening and display variant selection when external stress is applied during aging. The mechanism is believed to be the reduction of elastic strain energy caused by the precipitate/matrix lattice mismatch. Thus, the nature of the selection indicates that the sign of the misfit is positive along [010]p. Because the misfit strain energy increases with increasing precipitate size, variant selection occurs during coarsening.

Forming operations are known to be complex, involving many strain states, strain rates, temperatures, strain paths, and friction conditions. Material properties, such as strength and ductility, are large drivers in determining if a material can be formed into a specific part, and for selecting the equipment required for the forming operation. Predicting yielding behavior in situations such as these has been done using yield surfaces to describe material yielding in specific stress states. These models typically use initial mechanical properties, and will require correction if the material has experienced previous straining. Here, we performed interrupted uniaxial tensile testing of a 304 stainless steel to observe the effects of unloading and subsequent reloading on yielding and tensile properties. An increase in yield point developed, in which a higher yield was observed prior to returning to the bulk work hardening behavior, and the magnitude of the yield point varied with unloading conditions and strain imposed. The appearance of a yield point is attributed to strain aging or dislocation trapping at obstacles within the matrix. These results suggest that both strain aging and dislocation trapping mechanisms may be active in the matrix, which may present challenges when forming austenitic stainless and new advanced high strength steels that likely show a similar behavior. These results provide a potential area for refinement in the calculation of yielding criteria that are currently used to predict forming behavior.

In an effort to optimize the transportation of oil and gas, the pipeline industry is developing large-diameter, thick-walled pipelines that can withstand low temperatures and high pressures. In this study, three X70 steel plates of similar chemistry, ranging in thickness from 13.5 mm to 22 mm, were subjected to drop-weight tear and Charpy V-notch tests to determine the effects of plate thickness and microstructure on the formation of separations and impact behavior. Constraint induced by specimen thickness appears to dictate the location of separations, the three microstructures exhibited different separation behaviors, and microstructural banding was not found to promote separation formation. Separations were most frequent when the primary fracture plane was parallel to the rolling direction. This study also found that standardized empirical relationships between Charpy V-notch and drop-weight tear tests do not estimate to the advanced high-strength and -toughness steels investigated.

Titanium (Ti) alloys are ubiquitous in the aerospace, defense, and biomedical industries for their high strength to density ratios and good corrosion resistance. Ti alloys are typically optimized for strength, but improved work hardening characteristics and ductility would broaden their use in engineering applications. Here we show desirable combinations of strength and ductility, including a fourfold increase in yield strength, without commensurate losses in ductility, are exhibited, overcoming the strength/ductility tradeoff. This is achieved by nanoscale ω phase precipitates produced by natural and artificial aging, in concert with TRansformation Induced Plasticity (TRIP), in alloy Ti-10V-2Fe-3Al (wt.%) for the first time. These deformation mechanisms can be tailored to design microstructures, opening up the mechanical property and performance landscape for lightweight, Ti structural applications, analogous to the design of advanced high strength steels with unique properties for automotive applications that result in energy savings via lightweighting and crashworthiness

The microstructures and hardnesses of Co-10Al-9W-1C, Co-7Al-5W-1C and Co-7Al-5W (at %) alloys are reported. Homogenization of the Co-10Al-9W-1C alloy was unsuccessful at 1300 °C and both B2-CoAl and η carbide phases remained in the interdendritic regions. However, the lower-solute Co-7Al-5W-1C and Co-7Al-5W alloys did homogenize at 1300 °C. Upon aging the Co-10Al-9W-1C alloy at 800 °C, the undissolved η carbide transformed into D019-Co3W phase and subsequently into γ'-Co3(Al,W) phase, consistent with the higher stability of the γ' phase in the C-doped alloy. Also, high γ' volume fractions and low γ' coarsening rates were revealed by transmission electron microscopy in the various Co-Al-W-C alloys. These observations are explained by the effect of C on the phase equilibria and γ/γ' interfacial energy in the Co-Al-W system. Finally, the microhardness is increased while the density is decreased by alloying with C, which could result in higher specific strengths in the C-doped alloys.