Effects of ternary additions on martensitic transformation of TiAu

The effects of ternary element additions on martensitic transformation start temperature (Ms) and factors for controlling Ms 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 Ti50(Au, X)50 were fabricated by Ar arc-melting followed by a homogenization at 1173 K for 3.6 ks. Ms was measured by differential scanning calorimetry. It was found that the apparent phases at room temperature identified by θ − 2θ X-ray diffraction were B19 regardless of ternary additions. The correlations between Ms or the change in Ms by adding 1 mol% of X (ΔMs) are discussed in terms of electron atom ratio (e/a), valence electron number (Ne), Mendeleev number (NM) and lattice parameter ratio between c- and b-axes (c/b) of B19 martensite phase. It was found that Ms decreases linearly with increasing amount of ternary additions and that ΔMs is −40 K/mol% for Ru and −5 K/mol% for Cu, for example. Besides, the dependence of Ms on the above factors is presented and linear correlations are obtained.