目的 改善选区激光熔化(Selective laser melting，SLM)316L不锈钢的表面完整性和力学性能。方法 采用超声纳米晶表面改性(Ultrasonic Nanocrystal Surface Modification，UNSM)这一新兴表面塑性变形方法对SLM 316L不锈钢进行超声冲击强化，利用维氏硬度计、扫描电镜、白光干涉仪、EBSD、XRD等对处理前后材料的表面完整性、微观组织演变和塑性变形行为进行表征和分析。结果 经过UNSM处理后，SLM 316L不锈钢的微观缺陷明显减少，初始未熔合孔隙发生闭合，表面粗糙度Ra由5.374 μm降至0.510 μm，表面硬度从230HV增至461.16HV;同时，材料表层发生了剧烈的塑性变形，形变诱导材料微观组织从γ相向α相转变，微观结构由初始不规则柱状粗晶转变为等轴状细晶。从EBSD表征结果可知，在材料表面形成了深度约为20 μm的梯度纳米晶，材料内部存在明显的不均匀变形;与初始SLM试样相比，通过UNSM处理在材料表面引入了最大为932 MPa的残余压应力。结论 超声纳米晶表面改性能够显著改善SLM 316L不锈钢的表面完整性，形成较深的晶粒细化层和残余应力硬化层，从而有效提高其耐腐蚀性和疲劳抗性，是一项有前景的SLM后处理技术。

Metal powder additive manufacturing (AM) technologies, such as selective laser melting (SLM), have attracted considerable interest owing to their near-net forming characteristic and layer-by-layer building-up strategy, which allows overcoming the constraints of traditional manufacturing technology, achieving complex components in a short time of mass customization. However, the SLM process-induced micro-defects (i.e. pores, lack-of-fusion, and undesired microstructures) will result in not only poor surface finish and interior thermal cracks but also more dispersion of mechanical properties. Therefore, for a more homogenized microstructure and smaller material anisotropy, a novel surface strengthening method of severe surface plastic deformation, ultrasonic nanocrystalline surface modification (UNSM) was applied to improve the surface integrity and mechanical properties of SLM 316L stainless steel in this study.