The Use of Hard and Soft Sphere Models for the Evaluation of Lattice Distortion in B2 High-Entropy Shape Memory Alloys

Abstract

This paper considers the application of two known models for the evaluation of distortion in high entropy shape memory alloys with the B2 structure. Distortion was calculated using the hard sphere and soft sphere models for binary TiNi and senary Ti-Hf-Zr-Ni-Cu-Co alloys with different chemical composition. It was shown that both models could not be used because they gave a high distortion value even for binary Ti₄₉Ni₅₁ alloy. Distortion was so large for all alloys that they must be amorphous. However, this contradicted the experimental data according to which all alloys were crystalline with the B2 structure. A modification of both models was proposed taking into account that the TiNi alloy is an intermetallic compound. The formation of intermetallic compound was accompanied by a change in the spatial distribution of electron density around the nuclei of interacting atoms, which led to a change in the atomic sizes. The proposed modification gave the distortion value that was consistent with the lattice stability criterion for alloys where the concentration of each alloying element did not exceed 5 at %.