Evolution of functional properties realized by increasing laser scanning speed for the selective laser melting fabricated NiTi alloy

Abstract

The near equiatomic NiTi alloy was fabricated with selective laser melting method at a constant laser power coupled various scanning speeds from 300 mm/s to 480 mm/s. The evolution of functional properties was observed on cyclic tensile curves with emphases on the critical stress for inducing martensitic transformation and the mechanical recoverable strain. Results show that the critical stress for inducing martensitic transformation increases linearly with scanning speed, and the mechanical recoverable strain is indeed enhanced by increase of the scanning speed. Further, the highest mechanical recoverable strain of 2.29% is achieved at the applied strain of 4.5% in the sample fabricated with the highest scanning speed of 480 mm/s. The phase constitution, microstructural features and crystallographic texture were characterized in detail to interpret such evolution. It is found that the different Ms temperature and corresponding different phase constitution obtained with different scanning speed are mainly responsible for the variation of critical stress for inducing martensitic transformation and the mechanical recoverable strain. The co-existence of <111>//BD and <100>//BD crystallographic textures, as well as the variation of dislocation density show limited effect on the evolution amongst different samples.