Multi-index co-evaluation of metal laser direct deposition: An investigation of energy input effect on energy efficiency and mechanical properties of 316l parts

Abstract

Energy input in metal laser direct deposition (MLDD) could not only affect the energy efficiency of the process itself, but also influence the microstructure and resultant mechanical properties of the fabricated parts. This work takes the volumetric energy density as an energy input variable to explore the synergy mechanism of the high energy efficiency and excellent mechanical properties of 316L parts. For this reason, a multi-index co-evaluation framework was proposed to investigate the relationships between volumetric energy density and energy utilization ratio (EUR), specific energy consumption (SEC), micro-hardness, as well as tensile properties. Moreover, the causes of laser energy absorption/dissipation and microstructure/defect formation, along with the resultant energy efficiency and mechanical properties of 316L parts were thoroughly analyzed under different levels of volumetric energy density. The results demonstrated that increasing volumetric energy density can improve the EUR, indicating that more input energy has been effectively used to provide enthalpy change for metal materials. However, too high volumetric energy density will cause pores induced by gas entrapment, while too low volumetric energy density may result in bounding defects and lack-of-fusion of powder material. Accordingly, under the premise of ensuring few defects, lower energy density can help to improve the mechanical properties of 316L parts due to the fine-grain strengthening mechanism. In this work, the volumetric energy density of 218 J/mm3 can achieve trade-offs between the energy efficiency and mechanical properties of the deposited parts. The research offered an orientation for simultaneously realizing process energy efficiency improvement and parts performance enhancement in AM process through optimizing energy input parameters.