Hot tensile property and fracture behavior of as-cast Ni49Ti36Hf15 shape memory alloy produced by vacuum induction melting

Abstract

The as-cast ingot of Ni49Ti36Hf15 shape memory alloy was prepared by vacuum induction melting (VIM). Hot tensile properties of this alloy were investigated by hot tensile test at the temperature range of 800–1100°C and strain rate of 0.01s−1. Fracture surface of the samples was studied by Scanning Electron Microscopy (SEM) to better understand microstructure evolution and fracture behavior. The Ni49Ti36Hf15 alloy exhibited low ductility at all temperatures due to the presence of many second phase and carbide in the microstructures. At 1000 and 1100°C, dynamic recrystallization was dominant which led to better ductility in comparison with 800 and 900°C. The fracture surfaces of the specimen tested at 800 and 900°C indicated that fracture mode was brittle, which was apparent from the flat facets of fracture surface. It was found that, at temperatures of 1000 and 1100°C, due to the presence of dimples on the surface and cleavage surfaces, the fracture mode was quasi-cleavage fracture.