Phase equilibrium and martensitic transformation in near equiatomic TiPd alloys

The homogeneity range of the TiPd compound is experimentally determined from martensitic transformation behaviors of solution treated and aged specimens with various compositions and diffusion couple method, and then the phase diagram of TiPd binary system in Ti side is reinvestigated. The phase boundary of TiPd compound on the Pd side is almost constant at about 50.5 at.% Pd. On the other hand, that on the Ti side extends from 50.6 at.% Ti at around 873 K to about 51.8 at.% Ti at 1073 K. From the diffusion couple experiments, it is recognized that there is an A2(bcc) to B2 order–disorder transformation around 30 at.% Pd instead of a β-Ti and TiPd duplex phase region. It is also confirmed that the Ti3Pd compound is formed by a peritectoid reaction between β-Ti and Ti2Pd. From these results, we propose a new phase diagram of the TiPd binary system.