Enhancing reliability in laser powder bed fusion through substrate modification: microstructure, mechanical properties and residual stress

Laser additive manufacturing (LAM) is prone to excessive tensile residual stresses, leading to cracking or even failure, seriously hindering its wide application. Therefore, controlling residual stress to avoid crack formation and improve forming quality is crucial for reliable LAM. Most of the past research controls the residual stresses by modifying the process during the forming process, which is a very complicated method. In this study, through alterations in the form of a substrate to modify its restraint effect on the resulting structure and heat dissipation channels, the impact of them on the microstructure, defects, residual stress, and fracture characteristics to mitigate the likelihood of cracking in laser powder bed fusion (LPBF) was systematically studied. The results showed that the microstructure of all the specimens consists of fine dendritic, cytosolic, and columnar. Specimens with un-grooved substrates exhibited more holes and cracks, and solidification cracks were predominant. The crack density in specimens with grooved substrates was reduced by 71 %, reaching a relative density of 98.94 %. Tensile test results showed that the mechanical properties of the grooved specimens were excellent, with the tensile strength and yield strength higher than the un-grooved samples by 29 MPa and 11.7 MPa, respectively. And the results of the residual stresses indicated significantly lower tensile residual stresses in specimens with grooves, due to reduced restraint stresses and increased heat dissipation, mitigating the extent of crack propagation. These findings provided a simpler new approach to LPBF of crack-free components with excellent mechanical properties.