Cryo treatment and corrosion studies of nickel-titanium shape-memory alloy

Abstract

Nickel (Ni)-titanium (Ti) shape-memory alloy (SMA) is a functional material that has received a higher demand in aerospace industries, biomedical industries, actuator, and sensor industries owing to the property of superelasticity and shape memory effect. In addition, SMAs offer better mechanical and corrosion-resistant properties. In this current work, cryo treatment of NiTi alloy has been carried out to investigate the change in the properties. NiTi SMA prepared by powder metallurgy are cryo treated for 12 hours to 48 hours. Further, a corrosion study has been performed on the cryo-treated NiTi samples with the variation in corrosion time to know the effect on the morphology and the hardness. It is found that cryo-treated NiTi shows higher resistance to corrosion than the non-treated sample. The present work is an attempt to find out the effect of cryo treatment on the hardness and corrosion behavior of NiTi SMA. In the scanning electron microscope (SEM) analysis, it is observed that with the increase in cryo treatment time, NiTi (martensite) phase increases. Similar phases are present in both untreated and cryo-treated NiTi pellets. Out of all cryo-treated NiTi pellets, 24 hours cryo-treated NiTi has a lower percentage of corroded area with an increase in the corrosion exposure time. Corrosion preferentially starts at the pit area and progresses toward the Ti-rich area. The hardness value increased for 48 hours cryo-treated sample when compared with other cryo-treated and untreated NiTi pellets.