Effect of selective laser melting process on phase transition and tensile properties of NiTi shape memory alloys

TiNi shape memory alloys were prepared by selective laser melting (SLM). The effects of laser energy density on the phase transformation, microstructure, tensile properties, and shape memory properties of the NiTi alloys under the different printing combinations of process parameters were studied. The results show that, when the laser energy density is between 45 J·mm^‒3 to 85 J·mm⁻³, the relative density of the samples is above 99.5%. With the increase of laser energy density, the content of NiTi(B2) phase in the SLM-formed NiTi alloys decreases, and the phase transition temperature increases gradually. Nano Ti₂Ni precipitates exist in all the printed samples. With the increase of laser energy density, the precipitates change from the uniform point distribution to the semi-reticular distribution. The SLM-formed samples at the laser energy density of 47.62 J·mm⁻³ show the best comprehensive performance as the tensile strength of (783±3) MPa, the elongation after fracture of (13.9±0.2)%, the recovery rate of 100%, and the recoverable strain of 2.75% after 20 times of cyclic tensile at room temperature.