Microstructure and mechanical properties of Ni50.7Ti49.3 shape memory alloy fabricated by selective laser melting

Abstract

In this work, dense NiTi shape memory alloy (SMA) was fabricated by selective laser melting (SLM) under different laser powers (150 W, 210 W and 270 W). The effect of altered laser power on the microstructure and mechanical properties of NiTi SMA was studied by X-ray diffraction, differential scan calorimetry, optical microscopy and compressive test. The results indicated that the grains of SLM NiTi SMA changed from the uniform and fine honeycomb crystals to large square crystals with the increase of laser power. Meanwhile, the phase transformation temperature of SLM NiTi SMA increased with the increase of laser power, which resulted in the volume fraction of B19' phase in the matrix increased at room temperature. More importantly, when the laser power was 150 W, the SLM NiTi SMA had best compressive strength of 3302.7 MPa and fracture strain of 34.5%, which were better than most of the reported compressive properties in SLM NiTi SMA. This is mainly attributed to the fine and uniform honeycomb crystals in SLM NiTi SMA by 150 W.