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This study investigates the strain rate-dependent deformation behavior of cost-effective twinning-induced plasticity (TWIP) steel, Fe–26Mn-0.4C, at 15 K and reveals intriguing insights into its mechanical properties. The serration type changes from type A to type C with decreasing strain rate, resulting in a quasi-cleavage fracture at the crack initiation site. Microstructural analysis unveils a correlation between strain rate and the evolution of bundle twins, nano-twins, and ε-martensites. These denser networks of deformation twins (DTs) and ε-martensites contribute to impacting the mechanical properties. The mechanism behind the formation of serrations involves a rate-dependent thermal instability effect and the intricate interactions between dislocations and dislocations/Mn–C couples. The distinct findings enhance our understanding of the complex deformation behavior of high-Mn steel at cryogenic temperatures and provide valuable insights into the broader field of high-Mn steel applications in dynamic environments.

This study investigates the mechanical properties of a friction-stir-welded (FSW) AA6061-T6 aluminum alloy at ultra-low temperature (ULT) of 20 K. In-situ neutron diffraction and orientation imaging microscopy were employed to compare the tensile deformation behavior of the base metal (BM) and heat-affected zone (HAZ) in the FSW aluminum plate. The results demonstrate that compared to room-temperature (RT), ULT induces a significant improvement in tensile strength and ductility in both the BM and HAZ. The enhanced mechanical properties in BM at ULT result from a more homogeneous deformation than occurs at RT. On the other hand, HAZ at ULT exhibits an even lower yield strength than at RT, but the strain hardening rate (SHR) is the most significant among the alloys, leading to a tensile strength of 346 MPa and the highest ductility of 46.8%. The lowest yield strength corresponds to the lowest-hardness zones in HAZ, caused by dissolved/coarsened precipitates during the FSW process. The highest SHR in HAZ at ULT is attributed to the hardening of the {111} grain families and finer dislocation cell structures. The dislocation densities of both the BM and HAZ increased considerably during tensile deformation at ULT, which accounts for the improvement in tensile strength. Revealing the mechanism behind the remarkable improvement in the mechanical properties of FSW AA6061-T6 at ULT suggests its applicability for cryogenic applications.

Bimodal reinforcement consisting of powders of large graphite flake (GF) and small graphene nanoplatelet (GNP) were used to fabricate (GF + GNP)/Cu composites to reduce the anisotropy of the thermal and mechanical properties in GF/Cu composites. In this study, we investigated the effects of GNP addition on the anisotropy of the thermal and mechanical properties and the deformation behavior of (GF + GNP)/Cu composites. The 2 θ > value was used to evaluate the alignment of the reinforcing phases (GF, GNP), by which the variations in the coefficient of thermal expansion (CTE) and thermal conductivity (TC) of the composites were analyzed. With increasing GNP volume fraction, the angle (θ) at which the GF deviated from the in-plane direction increased. As a result, the anisotropy of the CTE in the in-plane and through-plane directions increased, whereas the anisotropy of the TC and mechanical strength decreased. Cracking was observed in both the specimens compressed along the in-plane and through-plane directions, whereas kinking was observed only in the specimens compressed along the in-plane direction. The deformation behavior and mechanical properties of the composites with bimodal reinforcement in the in-plane and through-plane directions were strongly dependent on the change in the alignment of the GF with the addition of GNP. The results clearly revealed the role of bimodal reinforcement in controlling the anisotropy of the thermal and mechanical properties of the (GF + GNP)/Cu composite, providing guidelines for optimizing the thermomechanical properties of high-performance (GF + GNP)/Cu composites.

The present study investigates the anisotropic microstructure, nanomechanical and corrosion behavior of Ti–13Nb–13Zr biomedical alloys, which were fabricated using the direct energy deposition (DED) method. The microstructure of the as-deposited material was studied using a field-emission scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). We found anisotropic mechanical behavior using nanoindentation from strain rate sensitivity and creep tests. For the maximum load of 50 mN, the x-y plane (normal to the building direction) shows better indentation hardness and lower strain rate sensitivity value (0.014) compared to the x-z plane (0.022) (parallel to the building direction). The difference in the indentation hardness was mainly attributed to the smaller equiaxed prior-β grains and finer α’ martensitic laths on the x-y plane. In terms of creep behavior, the x-y planes show better creep strength than the x-z plane. Meanwhile, both planes show a very high creep exponent, which signifies a similar creep mechanism, i.e., dislocation based. Moreover, we further found the anisotropic corrosion behavior using electrochemical tests. Corrosion results reveal that the x-y plane is more corrosion-resistant than the x-z plane. In summary, the x-y plane of the direct energy deposited Ti–13Nb–13Zr alloy possesses better strength and corrosion resistance due to its finer microstructure.

6061 aluminum (Al) alloys were asymmetrically rolled to apply shear deformation, and the effects of pre/post-aging treatment on the mechanical properties and texture evolution were analyzed. The texture was analyzed using electron backscattered diffraction (EBSD), and the formability and planar anisotropy of the specimen were evaluated using the r¯-value and Δr-value calculated from the plastic strain ratios (r-values). Regardless of the aging conditions (no aging, pre-aging, and post-aging), asymmetric rolling yielded higher strength than symmetric rolling. Pre-aged specimens, regardless of the rolling method (symmetric rolling or asymmetric rolling), exhibited higher strength than the post-aged specimens. To develop the //ND shear texture throughout the specimen, asymmetric rolling in a supersaturated solid solution without an initial precipitate was more effective than asymmetrically rolling an aged-hardened specimen. Considering the strength, formability (r¯-value), and planar anisotropy (Δr-value) of the 6061 Al alloy, the asymmetrically rolled pre-aged specimen had the best mechanical properties. These results show that the strength and formability of the 6061 Al alloy can be improved and its planar anisotropy can be reduced using a combination of asymmetric rolling and control of the aging sequence. This work demonstrates how the deformation and heat treatment of Al alloys could be used to increase the adoptability of Al alloys for automobiles.

Particle-reinforced metal matrix composites (MMCs) with high-volume-fraction of above 40% are highly attractive in the field of structural materials because they impart enhanced reinforcement properties to metals. However, high-volume-fraction MMCs are not widely used due to their brittleness. Therefore, overcoming the brittleness of the high-volume-fraction composites is the first step to disseminate the high-reinforcement-fraction composites. In this study, the interface bonding of 55 vol% Al/SiCp composites was strengthened by modifying the interface characteristics to achieve high plasticity of the high-volume-fraction composite. The interface bonding strengthening was conducted by thermal oxidation of SiCp reinforcement. The increased plasticity of the composites was observed as the 62.2% increased fracture strain in the compression test. The interface modification changed the crack path during a compression test from interface crack to reinforcement particle crack. To investigate the mechanism of interface modification, in-situ neutron diffraction experiments were performed under compression. When the plasticity is enhanced by the interface treatment, most fractures consist of reinforcement fractures rather than interface fractures. Therefore, it is confirmed that controlling the interface treatment is a key factor to improve the plasticity in high-volume-fraction composites. This work shed light on developing new composite material with high-volume-fraction reinforcement.

Influences of chemical dilution and the number of weld layers on residual stresses in a multi-pass low-transformation-temperature (LTT) weld were investigated by finite element modelling and neutron diffraction. A coupled thermal-metallurgical-mechanical (TMM) model that took into account the chemical dilution effect was developed to simulate the complex LTT welding phenomena. The model was strictly validated by comparing the predictions with experimental measurements and the results found good agreement between them. The results showed that a transformation strain caused by LTT martensitic transformation introduced large compressive residual stresses (−500 MPa) into the weld zone and the quantities were closely related to the chemical dilution between welding layers. Simulation results revealed that the chemical dilution helped mitigate the large localized tensile residual stresses by modulating the phase transformation process and a single LTT layer was sufficient to generate high compression near the weld surface (~2.5 mm), which suggests a great importance for repair welding. Keywords: Finite element analysis, Thermal-metallurgical-mechanical model, Martensitic transformation, Residual stress, Chemical dilution, Multi-pass weld

The objective of this study was to evaluate susceptibility changes caused by iron accumulation in cognitive normal (CN) elderly, those with amnestic mild cognitive impairment (aMCI), and those with early state AD, and to compare the findings with gray matter volume (GMV) changes caused by neuronal loss. The participants included 19 elderly CN, 19 aMCI, and 19 AD subjects. The voxel-based quantitative susceptibility map (QSM) and GMV in the brain were calculated and the differences of those insides were compared among the three groups. The differences of the QSM data and GMVs among the three groups were investigated by voxel-based and region of interest (ROI)-based comparisons using a one-way analysis of covariance (ANCOVA) test with the gender and age as covariates. Finally, a receiver-operating-characteristic (ROC) curve analysis was performed. The voxel-based results showed that QSM demonstrated more areas with significant difference between the CN and AD groups compared to GMV. GMVs were decreased, but QSM values were increased in aMCI and AD groups compared with the CN group. QSM better differentiated aMCI from CN than GMV in the precuneus and allocortex regions. In the accumulation regions of iron and amyloid β, QSM can be used to differentiate between CN and aMCI groups, indicating a useful an auxiliary imaging for early diagnosis of AD. Keywords: Alzheimer's disease (AD), Mild cognitive impairment (MCI), Quantitative susceptibility mapping (QSM), Gray matter volume