Thermoelastic phase transformation in TiNi alloys under cyclic instrumented indentation

Austenitic and martensitic TiNi shape memory alloys were studied by means of cyclic instrumented indentation with the purpose of documenting the phase transformation. Recovery indexes were determined from the energy absorbed during loading, unloading and reloading and their relation with the microstructure and shape memory properties established. Significant changes on the load–displacement curves, associated to the transformation phenomenon, were exhibited by both materials. Under spherical cyclic nanoindentation, a classic pseudoelastic behavior was observed in the austenitic alloy, which was characterized by high recovery indexes and constitutes the first experimental evidence of this property under such testing conditions. On the other hand, the martensitic alloy showed lower recovery indexes, as a consequence of a faster stabilization process of the martensite plates.