Tetsuya Matsunaga

A surface state (Es) is generated in the electronic band structure when a stacking fault (SF) forms due to the violation of the translational symmetry of a crystalline structure at dissociated partial dislocation cores. We found that Es demonstrates a linear relation with the SF energy (SFE), which was evaluated via transmission electron microscopy (TEM) for nonferromagnetic metallic solids, indicating that the SF width is determined by ES on the slip plane for each crystalline structure. Based on this observed relation, for lead, the SFE calculated using density functional theory (48 mJ/m2) is inconsistent with that evaluated via TEM (8 mJ/m2). Furthermore, the relation reveals various peculiarities of aluminum, such as the deep Es resulting from the projected bulk band widely spread beneath the Fermi level and the narrower SF compared with those of other face-centered cubic metallic solids.

Twinnability in face-centered cubic metallic solids is discussed from the viewpoint of wavenumber (k) space. The {111} deformation twinning is one of the main plastic deformation modes enabling the rearrangement of a mirror-symmetry lattice structure across a twin boundary. The crystalline rearrangement around 112¯ in k-space is triggered by changes in the electron density distribution caused by the strain-induced modulation of the electronic band structure around this orientation. This modulation is defined by the twinnability, ε112¯, which reflects the difficulty of the redistribution of electron density around 112¯. This index clarifies that the deformation twinning is suppressed in aluminum (Al) due to its large ε112¯ value. This result rationalizes the disorder between platinum and Al observed in conventional twinnability assessments based on stacking fault energy.

Abstract The effect of alloying elements on the martensitic transformation behavior of Ti–Pd series high-entropy shape memory alloys was investigated. Five compositions incorporating Zr, V, Ni, and Pt were synthesized. DSC analysis revealed that the coherency of the martensitic structure formed by the added elements is crucial for maintaining a high transformation temperature. The findings provide insights into the compositional design of high-temperature shape memory alloys with enhanced thermal stability and functional performance.