Ternary Element Effects of Nb and V Additives on the Low-Temperature Wear Behavior of NiTi-Based Shape Memory Alloys

Abstract

In this study, three different types of composite powders, NiTi, NiTiNb (20 wt.% Nb), and NiTiV (20 wt.% V), were produced using ball milling. The samples were then obtained using the P/M process. Dry sliding wear tests of the samples were performed at 23 and - 40 degrees C. The results showed that the binary NiTi sample exhibited considerably greater surface damage at - 40 degrees C than at room temperature. The least wear surface damage occurred in the NiTiV sample at both ambient temperatures. It was determined that adding 20 wt.% of Nb and V increased hardness to 695 and 818 HV, respectively. When the calculated wear volume loss values were examined, it was determined that NiTi and NiTiV alloys wore more at - 40 degrees C compared to room temperature. In NiTiNb, however, very similar wear values were obtained at RT and - 40 degrees C, which was explained by the Nb additive suppressing the Ms transformation and protecting the austenite phase. Besides, the wear volume loss values of the Nb- and V-added samples decreased to approximately 1/6 of those of the binary NiTi sample at an ambient temperature of - 40 degrees C. Overall, the COF values at - 40 degrees C for all samples were higher than those at room temperature.