Microstructural characteristics and corrosion resistance in molten Zn-Al bath of Co-Mo-Cr-Si alloys

Co-base alloys Tribaloy T-800 and Stellite 6 are widely used bearing materials in the galvanizing industry. Tribaloy alloys are strengthened by Laves intermetallic phase while Stellite alloys depend on carbide dispersed strengthening. The chemical composition influences the amount and mechanical properties of the strengthening phases in these alloys, which consequently influence the overall performance of the materials. Currently preferred compositions of alloys Tribaloy T-800 and T-400 are hypereutectic with primary Laves phase dendrites and interdendritic eutectics. A new hypoeutectic alloy Tribaloy T-401 with primary Co-rich dendrites and interdendritic eutectics is obtained by adjusting Cr, Mo, Si and C contents. The new alloy Tribaloy T-401 has better ductility than alloys Tribaloy T-800 and T-400. Tribaloy alloys T-800, T-400 and T-401 as well as Stellite 6 have been dipped in an Fe-saturated Zn bath containing about 0.22 wt.% Al at 470 °C for various lengths of time up to 604,800 s (168 h) to study their corrosion resistance. It is found that all four alloys have reacted with the Zn-Al baths. Tribaloy alloys outperform Stellite 6 in corrosion resistance in molten Zn-Al bath and Tribaloy T-401 performs best in terms of the thickness of reaction layer.