Investigate the effects of the substrate surface roughness on the geometry, phase transformation, and hardness of laser-cladded Fe-based metallic glass coating

In this research work, a novel investigation of the substrate surface roughness effects on the geometry, the phase transformation, and the hardness of a single laser-cladded track on nickel-free high nitrogen stainless steel used for biomedical applications. First, two samples were sandblasted using 40- and 100-grit Al₂O₃ abrasive and two other samples were polished using SiC 150- and 240-grit sandpaper to attain four levels of surface roughness. Second, the FeCrMoCB amorphous powder was deposited on each substrate sample using a laser power 2000 W, 45 mm/s scanning speed, and a spot size of 4 × 4 mm. The geometry of the cladded layers was measured using an optical microscope. Furthermore, X-ray diffraction examination was employed to analyze the structure and phases formed within the coating layer. Finally, the microhardness measurement had been carried out and the average values were recorded. The results showed that the width and height of cladded track are increased with the decrease of the substrate surface roughness due to the superior of cohesion force over the adhesion force between the molten coating material and the substrate. Contrary, the amorphous content percentage is increased with the increase of substrate surface roughness. The hardness measurements showed that polished substrate exhibited higher hardness values (1188 and 1278 HV0.1) than the sandblasted samples (1112 and 1196 HV0.1) which is affected by the amorphous content and the phases found within the coating layer. As a conclusion, the polished substrate (240-grit sandpaper) gave the optimum results in terms of geometry, phase formation and hardness.