Shape recovery and stress-induced martensite in TiNi following indentation and wear loading

We present initial findings that are suggestive of the potential for shape-memory and superelastic NiTi alloys to function as useful tribological materials. For example, surface-deformation made with a spherical indenter is found to be almost completely recoverable by the shape-memory effect. A similar form of strain recovery is shown to be possible in thin films and in wear-track profiles. When a martensitic material is subjected to pin-on-disk loading, a substantial fraction of the wear track cross-section can be recovered by heating. It is also shown that the martensite phase can be stress-induced in response to complex loading associated either indentation or pin-on-disk wear tests, indicating that transformational superelasticity may be able to ameliorate wear degradation in the same way that it can limit low-cycle fatigue damage accumulation. Since NiTi can readily be deployed as a sputtered thin film coating, it may be possible to confer these beneficial effects to base metal substrates such as aluminum.