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

Abstract

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°, 45°, 90°). The microstructure of SLM samples was characterized using optical microscope (OM) and scanning electron microscopy (SEM). Only the γ-Ni phase was detected in the X-ray diffraction (XRD) patterns of the SLM samples. The lattice constant of the γ-Ni phase in the SLM 45°sample was the lowest among these SLM samples. The value of the surface roughness of the SLM 45° specimen was the highest than other parts, while, the value of the surface roughness of the SLM 0° 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 μm) was evenly distributed in the SLM 0° sample, while, the roughest equiaxed grains (approximately 0.73–1.26 μm) was formed in the SLM 45° sample. Furthermore, the SLM 0° 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 × 10−6 mm3 / (Nm)).