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 A degrees 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.