为辅助理解金属材料高精密增材制造成形机理，本工作利用微米级选区激光熔化(micro-selective laser melting，M-SLM)技术制备了316L不锈钢，对其拉伸性能及断裂行为进行了研究，并对断后横向和纵向拉伸试样显微组织和断口形貌进行了表征与分析，对近断面塑性变形区的晶粒取向、晶界特征分布等进行了电子背散射衍射(EBSD)分析。结果表明：M-SLM制备316L不锈钢晶粒内部存在尺寸为100~300 nm的胞状组织结构，拉伸断口呈韧窝状，窝口直径80~500 nm，这使得316L不锈钢的横向平均抗拉强度达692.1 MPa，纵向平均断后延伸率达54.6%，明显优于传统SLM技术制备的316L不锈钢。M-SLM制备316L不锈钢在拉伸过程中奥氏体Σ3孪晶界的出现与晶粒取向有关，其在取向接近<111>的晶粒中较易出现。进一步分析指出，Σ3晶界的出现阻断了特殊晶界网络的连通性。通过基于EBSD的矩形截面法对共格Σ3 (Σ3_c)和非共格Σ3 (Σ3_ic)晶界进行了统计分析，显示316L横向拉伸试样近断口区的Σ3_c和Σ3_ic晶界数量百分比分别约为43%和57%，而纵向拉伸试样近断口区的Σ3_c晶界数量百分比提高至约70%。Σ3_c孪晶界的增加使得总晶界能降低，是导致M-SLM制备316L不锈钢纵向拉伸强度普遍低于横向拉伸强度的原因。

Compared with selective laser melting (SLM), the micro-SLM (M-SLM) technology offers the advantages of small spot diameter (< 20 μm), high forming precision (20-50 μm), and surface roughness (R_a) of up 1 μm, which implies that the M-SLM technology provides great potential for promotion and application in communication electronics, biomedical, and other fields in the future. In this work, 316L stainless steel was prepared using M-SLM, and its tensile properties and fracture behavior were studied. The microstructures of transverse and longitudinal tensile specimens were also investigated. In addition, the fracture morphology was characterized and analyzed, and the grain orientation and grain-boundary-characteristic distribution in the near-section plastic-deformation zone were further analyzed using electron backscatter diffraction (EBSD). The results showed that the 316L stainless steel prepared by M-SLM had a cellular structure with a size of 100-300 nm inside the grains. The tensile fracture was dimple-shaped, and the average dimple diameter was 80-500 nm, which allowed the transverse average tensile strength of the 316L stainless steel to reach 692.1 MPa, the longitudinal average elongation after fracture was 54.6%, which were obviously better than that of the 316L stainless steel prepared using traditional SLM. The appearance of austenite Σ3 twin boundaries in the stretching process of the 316L stainless steel prepared by M-SLM was related to the grain orientation, which could more likely appear in grains with an orientation close to <111>. Further analysis indicated that the appearance of Σ3 grain boundaries blocked the connectivity of the special grain-boundary network. Statistical analysis of the coherent Σ3 (Σ3_c) and incoherent Σ3 (Σ3_ic) grain boundaries using the EBSD-based rectangular-section method revealed that the amount percentages of Σ3_c and Σ3_ic in the near-fracture region of the 316L transverse tensile specimen were approximately 43% and 57%, respectively. Meanwhile, the amount percentage of Σ3_c in the same region of the 316L longitudinal tensile specimen increased to approximately 70%. The increase in the coherent Σ3_c twin boundary reduced the total grain-boundary energy, which explained why the longitudinal tensile strength of the 316L stainless steel prepared by M-SLM was generally lower than the transverse tensile strength.