Unraveling the Mechanism of Energy Utilization Efficiency Regulating Melt Pool Dimensions and Tensile Properties of 316L Stainless Steel in Laser Directed Energy Deposition

Energy density is a common but often inadequate parameter for predicting properties in laser additive manufacturing, as it fails to capture complex energy absorption dynamics. This study introduces energy utilization efficiency as a governing factor for melt pool characteristics in laser directed energy deposition (LDED) of 316L stainless steel. We demonstrate that at a constant energy density, energy utilization efficiency varies significantly with process parameters, ranging from conditions that cause lack-of-fusion to those that promote porosity. Experimentally, increasing energy utilization efficiency under constant energy density (90 J/mm) led to a five-fold increase in melt pool depth and a doubling of its area. This shift in energy utilization efficiency directly influenced tensile properties, with samples at moderate energy utilization efficiency achieving optimal yield strength (~428 MPa), ultimate tensile strength (~583 MPa), and elongation (~51.6%). Quantitative strengthening analysis revealed that dislocation strengthening contributed approximately 60% of the total yield strength, but its contribution decreased with excessive energy utilization efficiency due to grain coarsening. To overcome the limitations of energy density, we propose normalized enthalpy as a predictive design parameter. It shows a strong linear correlation with melt pool width, depth, and area, effectively integrating both process inputs and material thermal response. This work provides a fundamental insight into energy–material interactions and offers a physics-enhanced predictive tool that complements conventional energy density metrics for optimizing the LDED process.