Functionally graded materials of SS316L and IN625 manufactured by direct metal deposition

Direct metal deposition (DMD) is a layer-by-layer material addition process. Partial functionally graded material (FGM) blocks of size 26 mm wide × 34 mm thick × 32 mm height were 3D printed based on Taguchi’s L9 approach using a commercial DMD machine equipped with a diode laser. The parameters selected for FGM deposition were laser power, scan velocity, and powder feed rate. The metal powders used for deposition were Stainless Steel 316L (SS316L) and Inconel 625 (IN625). The novelty is the introduction of three gradient layers for joining dissimilar materials of SS316L and IN625. ASTM E8 tensile specimens were cut from each FGM block for testing and characterization. Tensile test results revealed that the thick-layered partial FGM specimen-6 had a high ultimate tensile strength (UTS) of 532.6 MPa at the sixth set of optimum parameters. This is due to the mixed presence of coarser and fine columnar grains and equiaxed grain microstructures. Based on the analysis of variance, scan velocity had a more significant effect on UTS and powder feed rate on micro-hardness. However, a maximum micro-hardness of 202.5 HV was observed in the gradient layers of the ninth sample at the ninth set of parameters. The fractography analysis revealed the ductile failure of specimens.