Analysis of mechanical anisotropy of additive manufactured 316L austenitic stainless steel

Abstract

Selective laser melting method is one type of indirect melting in additive manufacturing, which produces the products by applying high-energy heat source to melt the metal powder and building it up layer-by-layer. Because it has no limit in product design and available to build net-shape products without extra machining process, selective laser melting method is believed to be a next-generation production technique in manufacturing field. Despite these advantages, recent studies shown that microstructural features: strong texture, columnar grain, porosity, and molten pool boundary of SLM built material which created from its complex heat history cause mechanical anisotropy. The anisotropic and asymmetric mechanical behaviors of 316L stainless steel processed using selective laser melting, were investigated experimentally and theoretically by performing tension and compression tests along different directions of the sample. Significant anisotropic and asymmetric behaviors were observed due to the effects of microstructure and internal defects. Severe anisotropy in stress level and elongation were found in the tensile behavior, while compression behavior exhibited somewhat different yield strength and strain hardening with loading direction. The contributions of microstructural factors and porosity to anisotropic behavior were analyzed. Microstructure analysis and finite element simulations based on the real microstructure confirmed that pore shape is the primary reason for the mechanical anisotropy and asymmetry in tensile loading. In compressive test, the molten pool boundary effect and porosity effect were the dominant cause for mechanical anisotropy. This result supports a guideline for designing parts and the scanning directions used in selective laser melting.