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The demand for new advanced high strength steels (AHSS) has been increasing in the last few decades. A large part of this demand comes from automotive companies. We have produced a new complex-phase (CP) steel with 1200 MPa of mechanical resistance and 8% of elongation, called CP1200. In this paper the dilatometric and microstructural characterization of a newly produced CP1200 steel is presented. The new steel was produced by making changes to the heat treatment of the already industrially available CP1100. The microstructure was quantified using light optical microscopy (LOM) and electron backscatter diffraction (EBSD). The microstructure of both steels was compared to identify the origin of the mechanical properties improvement. A new microstructure distribution, with higher amount of bainite and smaller concentration of ferrite and martensite was identified.

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.

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 .

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.

The evolution of the crystallographic texture and lattice strain of uranium 6-weight percent niobium alloy samples are tracked during multiple deformation and heat treating cycles in an effort to understand and control the mechanical properties of the material following thermo-mechanical processing. The heavily twinned microstructure and low-symmetry crystal structure of U-6Nb result in multiple sequential active deformation mechanisms associated with distinctive deformation textures in strain ranges from 0-0.15 true strain. It is found that heating into the high-temperature γ-phase erases much of the texture formed during deformation at room temperature in the α′′-phase and resets the active deformation mechanisms. Through a small number of deformation/heat treat cycles to moderate strains, i.e., ~ 0.13 per cycle, the flow strength of the material is recovered to its original value. However, on the fourth such cycle, a reduction of strength is observed and the sample failed.

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.

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.

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.

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.