The use of micro selective laser melting (μ-SLM) enables product miniaturization, which is one of the megatrends in the metal processing industry and increasingly find its applications in biomedical and electronics industries. Among these, NiTi shape memory alloy (SMA) shows a great promise in functional micro-scaled components such as stent. There are inevitably some imperfections in SLM, but the imperfection formation in μ-SLM may not be the same as that in the conventional SLM. This work studies the imperfections in μ-SLM produced NiTi samples, with focus on defects, microstructure and thermal/mechanical behaviors. The effects of substrate material, laser-related process parameter and scanning strategy on defects such as porosity and cracks were analyzed, and a process window for “Scanning speed – Hatch spacing” was determined. Transformation peak was hardly detected in thermal behavior of as-printed and post heat-treated μ-SLM NiTi, resulting from microstructure inhomogeneity, Ti-rich impurity phases TiC_1−xN_x/Ti₄Ni₂O_x and precipitate Ti₂Ni, which were introduced by powder preparation, μ-SLM or post heat treatment. The as-printed NiTi shows higher compressive strength and fracture strain than the post heat-treated samples, reaching 2796.57 MPa and 27.80% on average, respectively, but the plateau stress-strain stage is indistinguishable due to inhomogeneous and localized stress-induced martensite transformation. The brittle Ti₂Ni phase was introduced in post heat treatment, leading to inhomogeneous microstructure and lower ductility. The underlying mechanisms revealed in these imperfections could serve as a guideline for defect control, process optimization, as well as post heat treatment methods for μ-SLM of NiTi alloy.

微选择性激光熔化（μ-SLM）的使用可实现产品的小型化，这是金属加工行业的大趋势之一，并且越来越多地应用于生物医学和电子行业。其中，NiTi形状记忆合金（SMA）在支架等功能性微尺度组件中显示出了广阔的前景。SLM中不可避免地存在一些缺陷，但是μ-SLM中的缺陷形成可能与常规SLM中的缺陷形成不同。这项工作研究了μ-SLM生产的NiTi样品中的缺陷，重点是缺陷，微观结构和热/机械行为。分析了基板材料，与激光有关的工艺参数和扫描策略对诸如孔隙率和裂纹等缺陷的影响，并确定了“扫描速度-舱口间距”的工艺窗口。通过粉末制备，μ-SLM或后热处理引入_1-x N _x / Ti ₄ Ni ₂ O _x和沉淀Ti ₂ Ni。印刷后的NiTi的抗压强度和断裂应变均比热处理后的样品高，平均分别达到2796.57 MPa和27.80％，但是由于应力马氏体的不均匀和局部性，平台应力-应变阶段无法区分。 。脆性Ti ₂在后热处理中引入了Ni相，导致微观结构不均匀和延展性降低。这些缺陷中揭示的潜在机制可以作为缺陷控制，工艺优化以及NiTi合金的SLM的后热处理方法的指南。