NiTi shape memory alloy (SMA) with nominal composition of Ni 50.8 at% and Ti 49.2 at% was additively manufactured (AM) by selective laser melting (SLM) and laser directed energy deposition (DED) for a comparison study, with emphasis on its phase composition, microstructure, mechanical property and deformation mechanism. The results show that the yield strength and ductility obtained by SLM are 100 MPa and 8%, respectively, which are remarkably different from DED result with 700 MPa and 2%. The load path of SLM sample presents shape memory effect, corresponding to martensite phase detected by XRD; while the load path of DED presents pseudo-elasticity with austenite phase. In SLM sample, fine grain and hole provide a uniform deformation during tensile test, resulting in a better elongation. Furthermore, the nonequilibrium solidification was studied by a temperature field simulation to understand the difference of the two 3D printing methods. Both temperature gradient G and growth rate R determine the microstructure and phase in the SLM sample and DED sample, which leads to similar grain morphologies because of similar G/R. While higher G×R of SLM leads to a finer grain size in SLM sample, providing enough driving force for martensite transition and subsequently changing texture compared to DED sample.

通过选择性激光熔化（SLM）和激光定向能量沉积（DED）增材制造（AM）具有标称成分为Ni 50.8 at％和Ti 49.2 at％的NiTi形状记忆合金（SMA），以进行比较研究，重点是相组成，显微组织，力学性能和变形机理。结果表明，SLM的屈服强度和延性分别为100 MPa和8％，与DED的700 MPa和2％显着不同。SLM试样的加载路径表现出形状记忆效应，对应于XRD检测到的马氏体相。DED的载荷路径呈现出奥氏体相的准弹性。在SLM样品中，细晶粒和孔在拉伸测试过程中提供均匀的变形，从而导致更好的伸长率。此外，通过温度场模拟研究了非平衡凝固，以了解两种3D打印方法的差异。两种温度梯度G和生长速率R决定了SLM样品和DED样品的微观结构和相，由于相似的G / R导致相似的晶粒形貌。SLM的较高的G × R导致SLM样品具有更细的晶粒尺寸，与DED样品相比，为马氏体转变提供了足够的驱动力并随后改变了织构。