Acta Materialia最新文献

This study proposes a method for predicting three-dimensional (3D) local strain distribution under compressive deformation of as-cast Mg/LPSO two-phase alloys from 3D microstructure images. The 3D local strain distribution was obtained by applying the digital volume correlation method to X-ray CT images before and after compression tests. Three microstructure descriptors were extracted from the 3D microstructure images around each strain measurement point: volume fractions of the phases, persistent diagrams that can express the connectivity of the phases, and two-phase spatial correlation that can express the spatial distribution of the phases. A deep learning model was then constructed to predict local strain from the three microstructure descriptors. Since two types of descriptors were used in this study, numerical data and image data, multimodal deep learning was employed to make predictions. Thus, the use of multiple microstructure descriptors enabled predictions to be made with higher accuracy than when predictions were made from a single descriptor. Feature importance of the descriptors was assessed through correlation analysis and occlusion sensitivity analysis. The results revealed that high strain tended to occur in the region where the hard phase, LPSO phase, had a large elongated phase oriented at a 45° direction to the loading direction. This result is consistent with other previous studies and indicates that the proposed method is effective in elucidating the relationship between the microstructure and the deformation behavior of the material.

Zero thermal expansion (ZTE) materials can solve problems such as device failure and cracking caused by mismatched coefficient of thermal expansion. However, ZTE material is rare in nature. NaZr₂(PO₄)₃ is a framework compound with near-zero thermal expansion due to coupled rotations of rigid ZrO₆ and PO₄ polyhedra in the structure, and several studies have been devoted to obtaining more ZTE compounds by chemical substitution of Na or Zr. Inspired by the AAV concept we proposed, in this work, the PO₄ tetrahedra with a small volume has been replaced by the large volume MoO₄ tetrahedra in K_xMn_xIn_2-x(MoO₄)₃ (x = 0.4, 0.6, 0.8, and 1.0) compounds to provide more space for the coupling rotation of the polyhedron, and reduce the coefficient of thermal expansion. On the other hand, the flexibility of the framework structure has been modulated by the content of K⁺ to achieve new ZTE materials, and the effects of K⁺ content on crystal structure and thermal expansion have been analyzed in detail by combining variable temperature XRD and Raman. These findings not only provide more ZTE materials, but also suggest a promising design method for ZTE materials.

The thermophysical properties and rapid solidification mechanism of liquid Mo-33.3 at.% Zr peritectic alloy were investigated by electrostatic levitation technique, which attained a maximum undercooling of 387 K (0.16 T_L). At its liquidus temperature, the density, surface tension, viscosity and solute diffusion coefficient of this refractory alloy were determined as 8.14 g/cm³, 1.60 N/m, 11.32 mPa·s and 1.41 × 10⁻⁹ m²/s, respectively. The primary (Mo) dendrite growth started from multi-point nucleation, while its growth velocity agreed well with the prediction of LKT/BCT dendrite growth theory and reached an upper value of 43 mm/s. The subsequent peritectic transition was characterized by a power-law kinetics relation between the nominal growth velocity of peritectic Mo₂Zr phase and peritectic undercooling, displaying a maximum velocity of 46 mm/s. The increase of liquid undercooling facilitated the completion of peritectic transition and refined the microstructure of residual primary (Mo) phase, thus enhancing the Vickers hardness of this alloy gradually up to 1190.9 HV at the maximum undercooling.

Fine-long shaped grains have been proved to be an efficient design approach to overcome the traditional trade-off relation between strength and electrical conductivity (EC) of metal wires. However, quantitative models linking grain shape parameters to both strength and EC remain scarce, limiting the precise optimization of material properties. In this study, grain boundaries (GBs) were classified into parallel or perpendicular ones to establish the quantitative models. Accordingly, a novel model for calculating the EC of fine-long shaped grains was proposed by first parallel-connecting the parallel GBs with the matrix, then series-connecting them with the vertical GBs. The EC calculated using this new model shows a small error band of only 0.5 %, indicating an excellent accuracy of EC calculation. Besides, a quantitative model for calculating the strength based on grain width was also developed. Consequently, the general effects of grain shape parameters including grain width, grain length, grain volume and grain aspect ratio on the strength and EC were quantitatively revealed. This work does not only advance the principle for achieving high strength and high EC through fine-long shaped grains from a qualitative concept to a quantitative framework but also offers valuable insights for the quantitative analysis of GB effects on strength and EC in other materials.

Molecular dynamics simulations were employed to understand the diffusion bonding process during hot isostatic pressing (HIP) of Al6061/Al6061 alloy. Simulations of the HIP process reveal atomistic phenomena that are difficult or unlikely to be observed experimentally and provide useful insights into the mechanism of diffusion and bonding. The results reveal that at the start of the HIP process, a massive incursion of oxygen atoms occurs from the pre-existing γ-Al₂O₃ to the 6061 region across the interphase interface. These oxygen atoms interact with the enriched Mg atom layer present at the existing γ-Al₂O₃ and 6061 matrix to form a secondary complex Mg₂Al₂O₅ phase. Diffusion calculations also show that transport of atoms due to the applied pressure is 4–5 orders of magnitude higher than would occur in the absence of HIP conditions. The Mg₂Al₂O₅ phase also provides efficient pathways for the rapid transport of Mg atoms. Because of the higher diffusion coefficients observed for Mg within the phase, Mg atoms can move more swiftly compared to their diffusion within other phases such as γ-Al₂O₃. This accelerated mobility facilitates the rapid movement of Mg atoms across the interface, leading to changes in the local composition and the potential growth of the Mg₂Al₂O₅ phase.