Effect of Ni Content on the Aging Behavior of Ti-xNi-12Hf (x=50.2 similar to 51.0)(at%) Alloys

Abstract

Ti-xNi-12Hf (x = 50.2 similar to 51.0)(at%) alloys were prepared by arc melting and then their aging behaviors was investigated using scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). All alloys consisted of Hf-rich (Ti, Hf) Ni, (Ti, Hf)(2)Ni and Ti-Ni-Hf matrix. The Hf-rich (Ti, Hf) Ni was known to be cubic, with a lattice parameter of a = 0.3192-nm, and have a chemical composition of 30.3 at% Ti, 39.8 at% Ni and 29.9 at% Hf. Oblate spindlelike (Ti0.6Hf0.4) Ni particles were precipitated in the Ti-50.2Ni-12Hf alloy with aging, while lens-like (Ti, Hf)(3)Ni-4 particles were precipitated in the Ti-50.7Ni-12Hf alloy. The DSC peak temperature (M*) corresponding to the B2-B19' transformation decreased by raising aging temperature in the Ti-50.2Ni-12Hf alloy, while it increased with an increase in aging temperature from 873 K to 923 K and then decreased.