The effect of energy input on reaction, phase transition and shape memory effect of NiTi alloy by selective laser melting

Abstract

Selective laser melting (SLM) is used to fabricate near-equiatomic NiTi alloy from Ni–Ti mixed element powders. The influence of energy input on formability, microstructure, phase transition and shape memory effect of the NiTi alloy (atomic ratio is 1:1) is studied. The results show that the as built specimens contain NiTi phase and stable phase transition. The macro-defect-free NiTi alloys can be built up well from 118.75 J/mm3 to 750 J/mm3. The width of the columnar NiTi phase and the amount of the equiaxed NiTi phase increase while the fraction of NiTi phase decreases with the increase of the energy input. The B2↔B19′ phase transition behavior enhances with the increase of the energy input. And the as built NiTi alloy fabricated at high energy input presents better shape memory effect (SME), its recoverable strain is about 5.17% under a pre-strain of 6%, which is close to those by conventional methods. Thus, SLM from mixed element powders can be regarded as a promising processing method to manufacture the NiTi alloy.