Build Optimization for Selective Laser Melting of 316L Stainless Steel and Parameterization for Cross-Material Comparison and Process Design

Optimization of selective laser melting process parameters with respect to microstructure and mechanical properties is examined for 316L stainless steel. Strength, ductility, and hardness are found to scale with power ratio, a proposed normalized melting intensity parameter accounting for the combined effects of process variables and material properties. Sound-build limits and the existence of an optimum power ratio are established. Poor properties at low power ratio are attributed to insufficient fusion, while property degradation above the optimum is correlated with increases in grain size and grain boundary defect frequency. Single-trace measurements are used to correlate power ratio with melt-pool cross-section dimensions, which are further shown to scale with curvature at the root of the melt pool, providing a direct bulk-build measure of the melting intensity. With strong correlation to the melt pool size, soundness of fusion, porosity, grain boundary defects, and mechanical properties, the utility of the power ratio as a design parameter is examined. By coupling the power ratio with a linear process rate and/or a dimensionless thermal dissipation time, sound-build process maps are used to assess reported data for several alloy systems, further demonstrating the value of the proposed parameterization as cross-material platform for process design.