Quasilinear pseudoelasticity and small hysteresis in SLM-fabricated NiTi

NiTi shape memory alloys with quasilinear and slim pseudoelasticity are desirable for high fatigue life and easy controllability. This paper reports that the selective laser melting (SLM) technique can encourage formation of quasilinear pseudoplasticity with small hysteresis of NiTi. The NiTi parts are found to present a high density of dislocations in the as-fabricated state. Deformation cycling of the defect-containing SLM NiTi parts promotes the formation of a unique microstructure consisting of nanocrystalline and amorphous-like phases. Such microstructure leads to a continuous and quasilinear type pseudoelasticity with small hysteresis. It is found that the scanning speed of laser affects the dislocation density and transformation behaviour, thus influencing the pseudoelastic behaviour of the SLM-fabricated NiTi. The transformation temperatures are shown to decrease while the transformation intervals to increase with increasing the scanning speed due to the increased dislocation density. The mechanically cycled SLM fabricated NiTi with a scanning speed of 850 mm/s exhibits a stable quasilinear pseudoelasticity of 5.8% and a small energy dissipation of 1.4 MJ/m3.(c) 2022 Elsevier B.V. All rights reserved.