Metallurgical characterisation of multi-track Stellite 6 coating on SS316L substrate

This article attempts to investigate the root cause of the possible failure of the cobalt-based Stellite 6 coating deposited on SS316L substrate using plasma-transferred arc welding through an extensive metallurgical and mechanical analysis by considering parameters such as contact angle, dilution and aspect ratio. The chosen sample with optimum input parameters, such as weld current 100-180 A, travel speed 100-180 mm/min, etc., having good mechanical properties but with traces of minor coating irregularities is thoroughly investigated for its metallurgical performance. Studies revealed that the Stellite 6 coating is dominated by the FCC cobalt and HCP cobalt along with carbides of different elements such as M7C3, M6C and M23C6 phases where M is tungsten and Chromium. Stellite 6 microstructure shows a hypoeutectic structure of dendrites rich in cobalt and interdendrites rich in chromium increasing microhardness. As arc current increases, percentage dilution increases, leading to a decrease in weld coating contact angle.