Effects of re-melting on interfacial morphology of 316L/Inconel 625 functionally graded material via innovative platform integrated in selective laser melting

Functionally graded materials (FGMs) are considered advanced materials whose properties change in a controlled manner in a specific direction or even in different directions within a component. FGM components are widely used in different industries such as aerospace, automotive and biomedical domains; however, fabricating FGM components with complex geometries using conventional methods encounters challenges. This study focused on the fabrication of FGM components using an innovative platform which was designed and integrated into the SLM machine, enabling the utilization of multiple powder materials. FGM components were fabricated using stainless steel 316L and Inconel 625 powder materials. Moreover, the effect of re-melting on interface regions was studied. It was observed that decreasing the material changing step and performing re-melting at the interface regions significantly reduced defects such as cracks, voids, and discontinuities. EBSD results showed the grain morphology transitioned from equiaxed in 100% Inconel 625 to columnar in 100% 316L, due to the thermal gradient and Re-melting facilitated grain growth in the interface regions. The XRD test results indicated that the re-melting process aided in the dissolution of carbides and precipitates, while also contributing to the formation of the NiO oxide phase. Furthermore, the elemental analysis showed a nearly linear trend in weight percentage variations. In addition, the hardness of the interface regions, where re-melting was performed, improved a maximum of 28% in comparison to the interface regions without re-melting. By employing the re-melting process and reducing the material changing step, the measured values of surface roughness in as-built side surfaces of components, which were alongside the height direction, decreased up to 30%.