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This work presents the amorphization of metastable β phase and the phase stability of the amorphous phase and non-equilibrium phase in a Ti-Zr-Nb-Sn shape memory alloy (SMA). The amorphous phases with lenticular shape uniformly embedded in β matrix are observed in the twin-jet-electropolished thin foil specimen for transmission electron microscope (TEM) observations. Meanwhile, a co-existence of non-equilibrium athermal ω phase and nanodomain phases are found to be formed in the β matrix. These non-equilibrium phases could favorably compete with the amorphous phase formation and render the amorphous phases are not formed, leading to that the amorphous phase is not observed in the bulk specimens for X-ray diffraction (XRD) and electron back-scattered diffraction (EBSD) and also TEM specimen prepared by a focused ion beam (FIB). The formation of the amorphous phase in the twin-jet-electropolished TEM specimen is thought to be due to the hydrogen-related artifacts introduced during twin-jet electropolishing.

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Minor addition of Gd and Zn can significantly improve the mechanical properties of extruded Mg-1wt.%Gd-xZn (x = 0, 0.5, 1 wt.%) alloys. However, how they modify the structure of alloys remains elusive. By using x-ray absorption fine structure, we found that Zn atoms tend to bond with Gd and the 0.5 wt.% Zn addition greatly reduces the coordination number (CN) of Gd atoms, forming an enhanced double solid-solution strengthening. Whereas, 1 wt.% Zn not only increases the CNs of Zn and Gd but also promotes the formation of minor Mg₃Zn₃Gd₂ phase. Compared with the grain refinement strengthening, it is found that the solid solution strengthening is not a dominant factor.

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Multi-metal composites have gained much interest in recent years to explore the unfilled space of the strength-elongation window. However, producing these composites is challenging and is limited to a few material combinations because most processing techniques involve melting/solidification and high-temperatures. This work demonstrates a new powder metallurgy-based approach to produce these composites using high-pressure torsion. Lamellar nano-crystalline composite with high entropy alloy (CoCrFeMnFe) matrix and uniformly distributed nickel-base superalloy (Inconel 718) reinforcement are realized after high-pressure torsion. The current approach has resulted in an excellent metallurgical bonded interface with an ultra-fine grain size in both the matrix and reinforcement. The samples showed an exceptional synergy of high yield strength ~900 MPa and elongation ~40%, overcoming the perennial challenge in multi-metal composites. The current approach is versatile and can open up a horizon of multi-material combinations with a synergy of strength and ductility.

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We report the discovery of a non-conventional {11-22} twinning mechanism in α-titanium through reversible α→ ω → α martensitic phase transformations. Specifically, the parent α-phase first transforms into an intermediate ω-phase, which then quickly transforms into a twin α-phase, leading to the formation of {11-22} contraction twins. In addition, we prove that the reversible α → ω → α phase transformations follow strict orientation relations between the parent α-, intermediate ω-, and twin α-phases. Finally, we demonstrate that our mechanism agrees with classical twinning theory in the shuffle, shear, and conjugate twinning plane. This study reveals the important role of the intermediate ω-phase in the twinning process, adding critical details to the existing mechanism of {11-22} twinning.

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The combined effects of vanadium additions and in-situ TiC particle formation upon the microstructure and mechanical properties of FeCrNiCu high entropy alloys were investigated. The addition of V changed the FeCrNiCu matrix structure from FCC (i.e., face-centered cubic) to FCC+BCC (i.e., body-centered cubic). The as-cast 10 vol.%TiC/FeCrNiCuV_0.1 high entropy alloy matrix composite showed excellent mechanical properties, with the yield strength and ultimate tensile strength determined to be 653.5 MPa and 1006.5 MPa, respectively. The extra strength generated by V addition and in-situ TiC particles in FeCrNiCu was evaluated, and the theoretical predictions match the experimental results well.

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The remarkable microalloying effect of nickel (Ni) on grain refinement and strengthening of selective laser melted titanium alloy is elucidated here. The addition of Ni up to ~0.4 wt.% avoided the formation of brittle eutectoid Ti₂Ni phase and an ultrafine and ductile microstructure consisting of nano-size lath α′ was obtained in selective laser melted Ti-0.4Ni alloy. The solid solution strengthening and refinement effect of Ni led to significant increase in strength from ~745 MPa for pure Ti to ~1120 MPa for Ti-0.4Ni alloy, and good elongation of 8.8%. It is underscored that microalloying of titanium alloys with Ni can enhance the properties of titanium alloys processed by additive manufacturing.

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A notable reduction of the stress corrosion cracking (SCC) initiation susceptibility was identified for machined cold-rolled 316L stainless steel that received a 650°C/10 hours heat-treatment prior to slow strain rate tensile (SSRT) testing in high-temperature hydrogenated water. The cracks per unit area of the machined surface of heat-treated specimens decreased by ~50% compared to as-machined surfaces, and by >70% with respect to polished surfaces. The results were ascribed to recrystallization of the ultrafine-grains present in the outer deformation layer of the machined surface, which resulted in a reduction of the tensile residual stress and nano-indentation hardness.

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Fine equiaxed grain regions are frequently observed in additively manufactured Inconel 718 alloy. Based on a grain-to-grain orientation analysis using EBSD, many assemblies of neighboring grains in these regions have been found to display multiple-twins orientation relationships sharing common ⟨110⟩ directions and exhibiting 5-fold symmetry. This is an experimental proof that the grain refinement observed in inconel 718 is due to Icosahedral Short-Range Order (ISRO) mediated nucleation mechanism. This is the first report of ISRO-mediated nucleation of fcc nickel which widens the perspectives on the microstructures control in additive manufacturing of Ni-based superalloys.

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A nanoprecipitates induced dislocation pinning and multiplication strategy is proposed for designing Cu alloys with high strength, plasticity and conductivity. That is, the nanoprecipitates act as obstacles and sources of dislocations. Additionally, the precipitation purifies the Cu matrix to guarantee the conductivity. To verify this strategy, dense dislocations and nanoprecipitates are introduced to a Cu-Fe-Ti alloy by solution treatment, rolling and aging. In-situ transmission electron microscopy straining and molecular dynamics simulations demonstrate that nanoprecipitates not only hinder the dislocation glide but also facilitate the dislocation multiplication, resulting in a tensile strength of 590 MPa combined with a uniform elongation of 6% of the alloy. The purification of the Cu matrix by the precipitation leads to an electrical conductivity of 69% IACS. Hence, this strategy paves a new avenue for developing high strength, high plasticity and high conductivity alloys.

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High energy X-ray diffraction microscopy (HEDM) was employed to index nearly 1000 grains in a polycrystalline Ti specimen and characterize their deformation during an incremental tensile test. For each grain, the positions of its associated diffraction peaks were used for analyzing its evolving crystal orientation and stress tensor. The azimuthal breadth of each peak at different load steps was measured, allowing measurement of initial yielding and providing an estimate of the dislocation density evolution in each grain. The Taylor hardening model was evaluated grain by grain using the above data, indicating that it can represent hardening in most grains. The yield stress and the strain hardening coefficient for all grains were statistically analyzed with respect to grain orientation, grain size, slip systems, and the surrounding neighborhood to examine how the yield stress and hardening are correlated.