Thermal expansion anisotropy of ternary titanium silicides based on Ti 5Si 3

Abstract

The anisotropy of the coefficient of thermal expansion (CTE) of Ti 5Si 3, defined as the ratio of the CTEs in the c and a directions, has a value of 2.7. In this paper we investigate the influence of ternary alloying additions on this value. Whereas Nb and Ta additions did not change the CTE anisotropy significantly, additions of V, Cr, Zr and Hf reduced it to values close to 2. According to Fu et al.'s ab initio model for the CTE anisotropy in 5–3 compounds with chain structures [Acta Mater. 51 (2003) 5083] the site occupations of the ternary alloying additions are crucial for determining the CTE anisotropy. These site occupations were determined for Zr and Nb additions and are consistent with the observed CTE anisotropy values.