Processing of IN718-SS316L bimetallic-structure using laser powder bed fusion technique

A crack-free Inconel 718 - Stainless steel 316 L bimetallic structure has been fabricated using the laser powder bed fusion (LPBF) process. Firstly, an optimum process parameter set resulting in defect-free bonding of both materials has been predicted by carrying out a parametric study. Thereafter, microstructural and mechanical characterization such as optical microscopy, X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, hardness and tensile testing have been carried out to investigate the characteristics of the bimetallic interface. The porosity quantification shows a density greater than 99.5% with no observable cracks or porosity at the transition zone. The secondary electron micrographs reveal a small inter-diffusion region at the interface. The interface and the nearby region consist of both cellular and columnar grains. The tensile strength of the bimetallic-structure approaches the strength of stainless steel 316 L. Even with the material discontinuity, the fracture happens at the weaker side (stainless steel 316 L) indicating the strong strength of the dissimilar interface. The fractography of the fractured surface displays a typical ductile cup and cone type of fracture. The results strongly suggest the suitability of the LPBF process for fabricating defect-free high-strength IN718-SS316L bimetallic structures.