Tribological behaviour of shape memory alloys

Abstract

This project aims to investigate the influencing factors on the coefficient of friction, and hence the ability to resist wear, of NiTi shape memory alloys. An extensive study of the effect of NiTi alloys in the martensitic phase in comparison with NiTi alloys in the austenitic phase, NiTi alloys in comparison with stainless steel and austenitic NiTi alloys using different counter-bodies, under different loading conditions were carried out. The phase transformation temperatures were measured by differential scanning calorimetry and the wear tests were conducted using a CETR tribometer at room temperature.

For the comparison of the wear behavior between martensitic and austenitic NiTi alloys, the result showed that the coefficient of friction of austenitic NiTi is significantly lower than that of martensitic NiTi. This means that the ability of austenitic NiTi to resist wear is much better than martensitic NiTi. For the comparison of the wear behavior of NiTi alloys and stainless steel, the result showed that the coefficient of friction of martensitic NiTi is higher than stainless steel but the coefficient of friction of austenitic NiTi is lower than stainless steel. The results of these two experiments were mainly attributed to the pseudoelasticity effect and the higher strength of the austenitic NiTi. For the comparison of the wear behavior between austenitic NiTi using different counter-bodies, the result showed that the coefficient of friction of the counter-body with the higher Vickers hardness is lower than that of the counter-body with the lower Vickers hardness. This result was attributed to the ease of deformation of the softer counter-body, hence leading to a larger real area of contact and a higher adhesion between the two interacting surfaces.