Effect of process parameters on the densities and cracking defects of SLM formed NiTi alloys

In this paper, the effects of laser power and scanning speed on the density and crack defects of NiTi alloy samples in selective laser melting (SLM) were investigated by all factor tests, and the effects of process parameters on the forming quality were evaluated comprehensively by the energy mass density. The results show that with the increase of energy density, the induced density increases first and then decreases, and the surface of the sample changes from microscopic crack defect to no defect and then to macroscopic crack defect. When the physical mass density is between 75 J/mm³ and 95 J/mm³, the density is maintained above 99.7%. With the increase of laser power or the decrease of scanning speed, the density of the sample increases first and then decreases. By exploring the influence of laser power and scanning speed on the forming quality of the sample with the same physical mass density, it is found that when the laser power is greater than or equal to 270 W, scanning speed is greater than or equal to 900 mm/s, laser power is less than or equal to 90 W, scanning speed is less than or equal to 300 mm/s, the density of the sample is lower than 99.5%, and keyholes and micro-cracks appear. When the laser power is 180 W and the scanning speed is 600 mm/s, the density is higher than 99.5% and there are no obvious defects.