Microstructure and Phase Transformation Temperature of NiTiNb Shape Memory Alloy Prepared by Laser Solid Forming Using Mixed Powder

Abstract

NiTiNb is a wide-hysteresis shape memory alloy. The Laser Solid Forming (LSF) technology can overcome the shortcomings of the traditional long cycle processing to prepare NiTiNb. In this work, we studied the microstructure and phase transformation temperature of the NiTiNb prepared by LSF., in which the Ni + Ti + Nb mixed powder was melted under different laser power P, scanning speed v, layer thickness t, and energy density EV. The results show that the combination of LSF process parameters with P = 2000 W and v = 900 mm/min can obtain a good metallurgical bond. As the laser power increases, the grain size increases, and the proportion of equiaxed crystals increases, the martensite transformation temperature increases. The inhomogeneity of the LSF-NiTiNb microstructure results in different phase transformation temperatures even in the same sample. The subsequent heat treatment at 850 °C for 3 h increases the phase transformation temperature and hysteresis of LSF-NiTiNb. The tensile properties of the LSF-NiTiNb samples with different building heights are significantly different. The maximum elongation reaches 8% and the minimum elongation is only 0.8%. The LSF parameter combination in this work has reference value for the parameter selection of subsequent preparation of NiTiNb.