Assessing the kinetics and mechanisms of corrosion of cast and HIPed Stellite 6 in aqueous saline environments

Cobalt–base (Stellite) alloys have seen extensive use in wear environments mainly due to their high strength, corrosion resistance and hardness. Co–base superalloys rely primarily on carbides, formed in the Co matrix and at grain boundaries, for their strength and the distribution, size and shape of carbides depends on processing conditions. Currently use of Stellite alloys has extended into various industrial sectors (e.g. pulp and paper processing, oil and gas processing, pharmaceuticals, chemical processing) and the need for improved information regarding corrosion (and often tribo-corrosion) of Stellite alloys has increased. It has been recognised that processing changes, which affect the microstructure of Stellite alloys, will most probably affect the corrosion performance.In this paper the corrosion behaviour of Stellite 6 in the as-cast and the HIP consolidated forms has been compared and contrasted using DC electrochemical techniques in static saline conditions. It has been shown that there is a significant difference in the corrosion performance of HIP consolidated Stellite 6 and it is possible to link the corrosion mechanisms to the microstructure. The benefits of using HIPing as a manufacturing process for the corrosion performance of Stellite 6 are discussed.