Revisiting the Ti-Pt system relevant to high temperature shape memory alloys

The Ti-Pt phase diagram was revised in light of new findings in the research related to the fabrication of alloys for high temperature shape memory alloy (HTSMA) application. This study focuses on alloys in the composition range 30-40 at.% Pt. Unfortunately, the Ti-Pt phase diagram is poorly understood in this composition range making the development of HTSMAs difficult. Consequently, alloys in this range were cast, heat treated, and characterized using differential thermal analysis (DTA), scanning electron microscopy (SEM), wavelength dispersive spectroscopy (WDS) and transmission electron microscopy (TEM). It will be shown that the peritectoid (Ti3Pt + β −TiPt →Ti4Pt3) proposed by Biggs and coworkers exists, but because of sluggish transformation kinetic, the high temperature DTA peaks are due to the transformation of β-TiPt to Ti4Pt3 and vice-versa; this sometimes produces a lamellar morphology when the alloys are cooled slowly from temperatures above 1240 °C. In addition, the alloys frequently contained more than two phases even after equilibration treatments. One of these phases is a new phase of approximate composition Ti5Pt3, which is believed to be stabilized by oxygen.