Effects of ternary additions on martensitic transformation of TiAu

Abstract

The effects of ternary element additions on martensitic transformation start temperature ( M s) and factors for controlling M s were investigated for the Ti–Au alloy systems. The ternary elements X selected were Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir and Pt, which substitute for the Au sites. The concentration of ternary elements was chosen to be 1 and 3 mol%. The alloys of Ti 50(Au, X) 50 were fabricated by Ar arc-melting followed by a homogenization at 1173 K for 3.6 ks. M s was measured by differential scanning calorimetry. It was found that the apparent phases at room temperature identified by θ − 2 θ X-ray diffraction were B19 regardless of ternary additions. The correlations between M s or the change in M s by adding 1 mol% of X (Δ M s) are discussed in terms of electron atom ratio ( e/a), valence electron number ( N e), Mendeleev number ( N M) and lattice parameter ratio between c- and b-axes ( c/b) of B19 martensite phase. It was found that M s decreases linearly with increasing amount of ternary additions and that Δ M s is −40 K/mol% for Ru and −5 K/mol% for Cu, for example. Besides, the dependence of M s on the above factors is presented and linear correlations are obtained.