Effect of Aging on the Microstructure and Shape Memory Effect of a Hot-Rolled NiTiHf Alloy

In this article, the effect of aging on the microstructure and shape memory effect (SME) of a hot-rolled Ni(49)Ti(36)Hf(15) alloy is studied. The alloy was prepared by vacuum induction melting (VIM) and homogenized at 1000 A degrees C for 2 h. The homogenized alloy was then undergone 45% hot rolling at 850 A degrees C and aging at temperatures of 500 and 600 A degrees C for 2 h. Optical microscopy (OM) and scanning electron microscopy (SEM) conducted on the hot-rolled samples revealed that hot rolling improves microstructure, deformation, and recoverable strains such that the alloy recovers 3.10 of 3.23 and 5.61 of 6.25 strain in the homogenized and hot-rolled state, respectively. Aging, however, adversely affects the formability and SME of the alloy, which stems from the embrittling effect of the newly formed precipitates during the aging process.