Microstructural evaluation of Stellite 6 and Stellite 6 reinforced with NbC particles coatings fabricated by laser cladding

The purpose of this investigation is microstructural evaluation of Stellite 6 and Stellite 6 reinforced with NbC particles coatings fabricated by laser cladding on AISI 5046 steel (used in the railway industry). For this scope, after preparing the powder by manual mixing, At first, the process parameters were applied on the substrate in a single pass. By microscopic studies and considering the desirable geometric characteristics of clad layer (height, width, contact angle, absence of crack, appropriate miscibility and uniform distribution of carbide particles in the matrix), the optimum sample was selected and then laser cladding was done with overlap 40% . In the next step, microstructural and hardness studies were done on the overlapping sample. For characterization and analysis of results, microstructural evaluation using Field Emission Scanning Electron Microscopy (FE-SEM), elemental analysis using Energy Dispersive Spectroscopy (EDS) and phase analysis using X-Ray Diffraction (XRD) were done. Stellite 6 powder laser cladding with a scanning speed of 10 mm/s and 900 W power was chosen as the optimal conditions for laser cladding. The clad was free of any kind of cracks and porosity and had a good metallurgical bond with the substrate. Laser cladding was done with 40% overlap and the coating thickness was measured as 1.2 mm. Laser cladding of Stellite 6/NbC powder with a scanning speed of 8 mm/s and 650 W power was chosen as the optimal condition for laser cladding. This coating also had no cracks and porosity and had a good metallurgical bond with the substrate. Laser cladding was done with 40% overlap and the coating thickness was measured from 400 µm to 1.5 mm. The microstructure obtained from the FE-SEM images of Stellite 6 and Stellite 6/NbC cladding from the side of the base metal towards the surface of the cladding showed that the microstructure is initially planar dendrite, after which the microstructure changes to cellular dendrite, columnar dendrite and coaxial dendrite respectively, which is the reason Changing the cooling rate and creating different structures along the cladding. The microstructure of Stellite 6 was composed of γ-phase with FCC structure and microstructure of Stellite 6/NbC It showed the uniform distribution of carbide particles in the field. The results of the XRD test proved the existence of peak Co in Stellite 6 and peaks Co and NbC in Stellite 6/NbC. The result of microhardness showed the The Stellite 6/NbC cladding has a higher hardness than the Stellite 6 cladding and base metal.