Experimental study on wear properties of NiTi shape memory alloy thin film

The hardness and wear behavior of NiTi Thin Film Shape Memory Alloy (SMA) at micrometer scales were studied systemically. A triboindenter (Hysitron Inc., Minneapolis, USA) was used to conduct a series of indentations under various loads (from 1000μN to 8000μN) and wear by scanning scratch method at temperatures from 22°C to 120°C. It was found that with increasing temperature, the hardness of NiTi thin film increased while its wear resistance decreased. The observed anomalous variation of wear resistance with hardness value is further analyzed by the interplay of phase transition and plasticity. Furthermore, cyclic scratch tests were conducted at various temperatures to examine the scratch behaviours of the film. It shows a superior scratch resistance within the testing temperatures between 22°C and 120°C, except that the corresponding physical mechanisms are different at low, mediate and high temperatures. Such superior scratch resistance is attributed to Shape Memory Effect at low temperature, while it is attributed to Superelasticity at mediate and high temperatures