选区激光熔化成形316L不锈钢微观组织及拉伸性能分析

采用选区激光熔化技术制备了316L不锈钢的拉伸试样,分析了试样不同区域的组织特征,测试了其拉伸力学性能.结果表明,其组织形貌主要为胞状晶,但在某些“微熔池”内晶粒生长方向不相同,而近乎相互垂直,从而在同一视野中显示出典型的细小柱状晶（亚晶）和近似六边形“胞晶”共存的组织特征.试样的抗拉强度与传统工艺制备的相比有较大提高,但断后收缩率有所降低.这主要由于选区激光熔化是快速熔化与冷却凝固的过程,其选区熔化的特征使得不同区域的激光入射角度、选区熔化扫描方式、“熔池”散热条件各不相同,导致不同区域呈现复杂的结晶过程,形成不同特征的微区组织.由于冷却速度较快所得的细小柱状晶的直径为亚微米级,致密分布,显著提高了材料的抗拉强度.但由于晶粒生长明显的方向性,使得拉伸过程中晶粒在不同方向的塑性变形不均匀,相互牵制,加之大量熔合线界面处不可避免的内应力,导致断后收缩率有所降低.

Microstructure and tensile properties of selective laser melting forming 316L stainless steel

The selective laser melting technology shows great advantages in the field of manufacturing of complex parts, but the organization and the comprehensive performance of the specimens have yet to be further optimized. Specimens of 316L stainless steel were fabricated by selective laser melting technology, the microstructure characteristics of different regions were analyzed, the tensile mechanical properties were tested. The results showed that the micro-structure were mainly cell crystal. However, the grain growth direction were different in some "micro-melting pools", and almost perpendicular to each other, which showed a small typical columnar crystal in the same field of view (subgrain) and "hexagonal cellular crystal" coexistence of micro-structure characteristics. Compared with the traditional specimens, the tensile strength of had greatly improved, but the elongation decreased. This was mainly due to the fact that SLM was a process of rapid melting and solidification which maked the difference of laser incident angle, scanning strategy and heat dissipation conditions resulting in complex crystals at different regions and different microstructure. The fine columnar crystal formed by rapid cooling that was submicron order and densely distribute was the main reason of the increases in tensile strength. However, the obvious anisotropy of grain, which resulted in the uneven deformation of grain in different directions and restrained mutually during the tensile test, and the inevitable remarkable internal stress at the interface of fusion lines leaded to a decrease in elongation.