Hot Deformation Behavior of NiTiHf Shape Memory Alloy Under Hot Compression Test

In this study, the hot deformation behavior of Ni₄₉Ti₃₆Hf₁₅ alloy was investigated. Compression tests were carried out at temperatures ranging from 800 to 1100 °C and at the strain rates of 0.001–1/s. The peak stress decreases with increasing deformation temperature and decreasing strain rate, a behavior which can be described by plotting the Zener-Hollomon parameter as a function of stress. It was realized that dynamic recrystallization (DRX) was responsible for flow softening. Most of the samples exhibited typical DRX stress-strain curves with a single peak stress followed by a gradual fall down stress. Microstructure evolution showed that new recrystallized grains formed in the vicinity of grain boundaries. The hyperbolic-sine-type constitutive model of Ni₄₉Ti₃₆Hf₁₅ alloy was obtained to provide basic data for determining reasonable hot-forming process. The activation energy for hot deformation of the Ni₄₉Ti₃₆Hf₁₅ alloy was close to 410 kJ/mol.