Effect of building directions on the surface roughness, microstructure, and tribological properties of selective laser melted Inconel 625

To study the effect of the building directions on surface macro- / micro- structure and tribological properties of Inconel 625 samples manufactured by selective laser melting (SLM) technology, parts were fabricated in three different building directions (0 degrees, 45 degrees, 90 degrees). The microstructure of SLM samples was characterized using optical microscope (OM) and scanning electron microscopy (SEM). Only the gamma-Ni phase was detected in the X-ray diffraction (XRD) patterns of the SLM samples. The lattice constant of the gamma-Ni phase in the SLM 45 degrees sample was the lowest among these SLM samples. The value of the surface roughness of the SLM 45 degrees specimen was the highest than other parts, while, the value of the surface roughness of the SLM 0 degrees sample was the lowest. The surface microstructure of the SLM samples was primarily composed of columnar dendrites and equiaxed grains. Among these samples, the finest equiaxed grains (about 0.38 - 0.63 mu m) was evenly distributed in the SLM 0 degrees sample, while, the roughest equiaxed grains (approximately 0.73-1.26 mu m) was formed in the SLM 45 degrees sample. Furthermore, the SLM 0 degrees specimen showed the highest microhardness value (332 HV0.2) and the best tribological performances, such as the lowest average coefficient of friction (COF = 0.31) and the wear rate (57.2 x 10(-6) mm(3) (N.m)).