Martensitic transformation and elastocaloric effect of Ti–Ni–Cu–Al microwire

Abstract

Phase transformation behavior and elastocaloric effect have been studied in a microwire (~200 µm in diameter) of a Ti-44Ni-5Cu-1Al (at%) alloy. The microwire was fabricated by cold drawing followed by annealing at 673 K for 10 min. The microwire exhibited large superelastic strain of ~5% with a small stress hysteresis of ~80 MPa at room temperature when a stress of 400 MPa was applied. The microwire also exhibited a large elastocaloric effect; the adiabatic temperature decrease caused by stress removal from 400 MPa reached 14 K, which is consistent with the value expected from the Maxwell relation. No remarkable deterioration in superelasticity and elastocaloric effect was observed up to 600 stress cycles. Nanoscale microstructure with grain width of ~40 nm is probably the main reason for the excellent fatigue resistance.