Microstructure and Thickness Effects on Impact Behavior and Separation Formation in X70 Pipeline Steel.

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.

Texture evolution as a function of scan strategy and build height in electron beam melted Ti-6Al-4V.

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 ß-Ti reconstructions obtained from as-built crystallographic orientations revealed spot melt scan strategies produced finer equiaxed/columnar grains with clear 001 ß build direction fiber textures, whereas the raster scan strategy produced large columnar grains and a weaker 001 ß 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 ß 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 ß 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.

MAUD Rietveld Refinement Software for Neutron Diffraction Texture Studies of Single­ and Dual­Phase Materials.

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.

High Throughput Discovery and Design of Strong Multicomponent Metallic Solid Solutions.

High Entropy Alloys (HEAs) are new classes of structural metallic materials that show remarkable property combinations. Yet, often times interesting compositions are still found by trial and error. Here we show an "Effective Atomic Radii for Strength" (EARS) methodology, together with different semi-empirical and first-principle models, can be used to predict the extent of solid solution strengthening to discover and design new HEAs with unprecedented properties. We have designed a Cr45Ni27.5Co27.5 alloy with a yield strength over 50% greater with equivalent ductility than the strongest HEA (Cr33.3Ni33.3Co33.3) from the CrMnFeNiCo family reported to date. We show that values determined by the EARS methodology are more physically representative of multicomponent concentrated solid solutions. Our methodology permits high throughput, property-driven discovery and design of HEAs, enabling the development of future high-performance advanced materials for extreme environments.