Corrosion behaviour assessment of cast and HIPed Stellite 6 alloy in a chloride-containing environment

• We have assessed the corrosion behaviour of as cast and HIPed Stellite 6 alloy.
• The corrosion behaviour has been investigated in naturally aerated 3.5% NaCl solution.
• We have used electrochemical impedance spectroscopy and polarization methods.
• HIPed Stellite 6 alloy shows a superior corrosion resistance compared to the as cast material.
• Microstructure plays an important role in determining the corrosion behaviour of Stellite 6 alloy.

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 wear resistance. The distribution, size and shape of carbides depend on processing conditions. Currently, the 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 of Stellite alloys has increased. It has been recognized that processing changes, which affect the microstructure of Stellite alloys, most affect corrosion resistance.In this work the corrosion behaviour of Stellite 6 alloy in the as-cast and the HIPed consolidated forms is compared and contrasted using DC and AC electrochemical techniques in static saline conditions. The results show that there is a significant difference in the corrosion performance of HIP consolidated Stellite 6 and it is possible to link the corrosion behaviour to the microstructure. The benefits of using HIPing as a manufacturing process for the corrosion performance of Stellite 6 are discussed.