Wear and Tribology Behavior of Superelastic Ni-Ti Tubes under Fatigue Cycling in Compression

Compressive loading of shape memory alloys (SMA) is gaining considerable attention in recent years due to the improved fatigue life compared to tensile loading. This can be beneficial in applications such as dampers, actuators, and particularly elastocaloric cooling. SMA elements, however, tend to buckle under compressive loading and their stability can be enhanced by utilizing properly designed holders, i.e., structures that support SMA elements and prevent them from buckling. On the other hand, these supporting structures are in contact with SMA elements, which can cause wear and their premature failure, intensified by the lateral expansion of material under compression. In current literature, a majority of experiments are focused on reciprocating sliding wear of tungsten carbide or variations of bearing steel balls/discs/pins/rings on NiTi plates as well as on comparison of wear performance of NiTi with other materials. The aim of this present work is to theoretically and experimentally study tribological conditions between the tube and supporting element (bushing) and to find the most compatible material to NiTi in order to minimize wear, provide adequate structural support, and finally to enhance the overall fatigue behavior.