Introduction to elastically isotropic [formula omitted]-Ti alloys

Abstract

This paper presents application of an electronic-based approach to the design of elastically isotropic and metastable β-Ti alloys. A systematic ab initio calculations were performed to predict the elastic properties of binary and ternary alloys, considering the 3d and 4d transition metals as solute elements. It was found, that at specific average concentration of valence electron e/a = 4.72, the binary and ternary Ti-based 3d alloys are elastically isotropic. The same properties are achieved at smaller e/a = 4.59 when 4d metals are used for alloying. As a result, three lightweight elastically isotropic β-Ti solutions were designed: Ti-46Mo, Ti-17Fe-7Cr and Ti-17Fe-13V wt.% with a significantly reduced concentration of alloying elements relative to the only known elastically isotropic Ti-72V wt.% system. Investigation of the generalized stacking fault energy of two {110}〈111〉 and {112}〈111〉 slip modes of body-centered cubic (BCC) lattice indicates that isotropy of elastic properties does not yield the same isotropy in terms of plastic deformation. Analysis of the electronic structure of materials with diversified elastic anisotropy reveals also that isotropic systems display transition of the bond character from direct covalent to more delocalized metallic bond. This transition together with electrostatic ion-ion interaction and number of valence electrons control the elastic anisotropy of BCC transition metals and alloys.