Through-thickness microstructure and wear resistance of plasma transferred arc Stellite 6 cladding: Effect of substrate

Stellite 6 is a cobalt-based superalloy having excellent high-temperature corrosion and wear resistance. In the present study, stellite 6 is deposited on two different substrates, namely, AISI 304L austenitic stainless steel and 9Cr-1Mo tempered martensitic steel through a plasma transferred arc (PTA) cladding process. Scanning electron microscope coupled with electron probe microanalysis, micro-hardness measurements and pin-on disc wear tests were deployed for investigating the effect of varying microstructure across the thickness and the substrate/ cladding interface on the tribological behaviour. For the first time, a systematic report on the variation of wear resistance of the cladding as a function of the location of examination across the thickness (top, mid-thickness, and cladding/ substrate interface) of the PTA Stellite 6 cladding is reported. It was found that the top part of the cladding had a refined microstructure with a higher fraction of chromium carbide as compared to the middle portion of the cladding in the case of both the substrates. Significant improvement in hardness and wear resistance was achieved for the cladding compared to both substrates. However, there was a significant difference in the thickness of the dilution zone. It was found to be 9.1 ± 1.3 µm in case of AISI 304L stainless steel compared to 6.0 ± 0.6 µm in 9Cr-1Mo steel. This was attributed to the higher thermal conductivity of 9Cr-1Mo steel than AISI 304L stainless steel. The micro-hardness profiles, wear-resistance, and the micro-mechanism(s) of wear across the coating corroborated with the observed microstructures.