Comparison of melt evolution and flow mechanisms of Inconel 718, Ti6Al4V, 304 stainless steel, and AlSi10Mg manufactured by laser powder bed fusion, structures, and properties after heat treatments

Abstract

Process parameters and material type are the key influencing factors in laser powder bed fusion (LPBF) manufacturing. In this study, a three-dimensional high-fidelity discrete heat-flow-coupled model was developed to study the surface morphology, melt evolution, and defect formation mechanisms of four types of alloys formed using LPBF under different laser processes at the powder scale to optimize the process parameters. Four alloys were manufactured by LPBF with optimal process parameters. Multiple characterizations were adopted to disclose the effect of heat-treatment on the microstructure and mechanical properties of the as-built parts of four materials. During LPBF forming, the melts developed from continuous and semicylindrical to discontinuous and “medicine spoon”-shaped at low and high linear energy densities (LEDs), respectively. The Ti6Al4V powder bed exhibited a long trailing melt pool and acted deeper (i.e., keyhole mode). The AlSi10Mg powder bed exhibited a smaller melt pool and did not exhibit trailing (i.e., heat-transfer mode). For Inconel 718 alloy and AlSi10Mg alloy, the improvement of mechanical properties is due to the precipitation of nanoparticle phase. The equilibrium of α+β phase results in the ideal strength and plasticity of Ti6Al4V alloy. The gradual disappearance of the cellular substructure reduces the strength of 304 stainless steel, but increases the plasticity. Process parameters correlate simulations with experiments and establish a "process-structure-properties" system. This study provides insights into melt evolution and flow behavior and is a reference for selecting and optimizing materials, laser-process parameters, and heat treatment regimes in practical engineering.