Actuation of single-crystal NiTi and NiTiHf shape memory alloys: An atomistic study

Abstract

Achieving thermal actuation in shape memory alloys (SMAs) requires subjecting the material to cyclic thermal processing. This process involves carefully regulating the heating and cooling of the material to trigger the desired superelasticity and shape memory effect (SME) in the SMA. To investigate the influence, the temperature rate, and constant stress on the thermal actuation behavior of NiTi and NiTiHf alloys, this study used molecular dynamics (MD) simulations on equiatomic NiTi and a Ni-rich NiTiHf high-temperature shape memory alloy (HTSMA). Transformation temperatures for both alloys were first determined to define the temperature range used during actuation. The constant stress applied during actuation was based on the plateau stress associated with the martensitic transformation under loading. Thermal actuation was then simulated on thick plate models at various temperature rates. The results demonstrated that while the actuation strain remains largely unaffected by the temperature rate, a decrease in temperature rate leads to significantly narrower thermal hysteresis in the strain–temperature response.