A study on the mechanical behavior and microstructural evolution of Ni60wt%-Ti40wt% (60Nitinol) intermetallic compound during hot deformation

The mechanical behavior and microstructural evolution of Ni60wt%-Ti40wt% during hot deformation were investigated. The compression tests were carried out at the temperature range of 900-1050 deg. C and at the strain rates of 0.001-0.35 s-1. Besides, the effects of strain on the hot working behavior, flow stress, activation energy and strain rate sensitivity were studied. The microstructural evolution was characterized using optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The results show that there was a delay in the occurrence of DRX as the deformation temperature increased from 950 to 1050 deg. C. The results also indicate that the activation energy and the strain rate sensitivity of Ni60wt%-Ti40wt% alloy vary abnormally with strain. The possible mechanisms dominated during the hot deformation of this alloy were determined and discussed. These results imply that there is a temperature and strain rate range when the workability of this alloy is significantly reduced. For example, there are some abnormalities in the flow curve when the deformation temperature drops below 950 deg. C. The lack of sufficient workability of 60Nitinol can be attributed to the high volume fraction of intermetallic compounds. It can be concluded that dynamic recrystallization can be considered as the dominate restoration mechanism. With increasing the strain from 0.2 to 1, the dynamically recrystallized grains become more prevalent. At the strain of 1.0, the DRX phenomenon has extended significantly so that there is almost no sign of the initial grains. Finally, a theoretical model was developed for the hot-deformation behavior of this alloy.