Effect of Vanadium on the Microstructure, Transformation Temperatures, and Corrosion Behavior of NiTi Shape Memory Alloys

Abstract

Ni50Ti50-xVx (x = 0, 1, 2, 3 at%) shape memory alloys were prepared by vacuum induction melting. They were homogenized and then hot rolled. Carbon hydrogen nitrogen oxygen sulfur (CHNOS) and X-ray diffraction (XRD) analyses were carried out on the alloys to find out the oxygen and carbon contents and the phases present in the alloys. Transformation temperatures determined by differential scanning calorimetry indicate that the addition of vanadium reduces the transformation temperatures. Corrosion studies were carried out in Hanks’ solution, while potentiodynamic polarization tests were done to calculate the rate of corrosion of the alloys. Two significant parameters were analyzed from the Tafel graph, namely, corrosion rate and corrosion potential. A comparison of these properties of the alloys was also made with commercially pure titanium and binary NiTi alloys. Among the NiTiV alloys, Ni50Ti47V3 (at%) alloy was found to undergo the least rate of corrosion. With the increasing vanadium content, the rate of corrosion was found to decrease. Scanning electron microscopy (SEM) analysis of the corroded surface shows that pitting was the main mechanism of corrosion in these alloys. Results show that the addition of V to NiTi has a positive effect on the corrosion properties of the alloys. Elaborate results are discussed in detail in this article.