Superelasticity decay of porous NiTi shape memory alloys under cyclic strain-controlled fatigue conditions

This paper presents some recent results on fatigue and pore deformation behavior of a porous superelastic NiTi shape memory alloy (SMA), fabricated by capsule-free hot isostatic pressing, under cyclic compression strain; and a systematical comparison was made with that of the dense NiTi SMA. The results show that the porous NiTi SMA has very good deformation recovery ability, in terms of a linear superelasticity as high as 4%. Under a high-cyclic strain level applied, the irrecoverable pore deformation occurs, which results in residual strain; and the degradation of superelastic effect only occurs in the first fatigue cycle, thereafter the good linear superelasticity is maintained. It has been shown that the fatigue of the porous NiTi SMA occurs at a relatively lower strain level compared with the dense one.