Melting index of plasma sprayed molybdenum silicide characterized by constitutions and its effect on oxidation kinetics

For plasma sprayed coatings, melting degree is an important indicator to characterize microstructure and related performance. In present work, it was interesting to define melting index, M.I. by the constituent phases in the case of plasma sprayed MoSi2 based coatings. The M.I. of coatings increased with the improved spraying power till 40 kW, then kept steady when the spraying power exceeded 40 kW. Meanwhile, the amount of metastable β phase firstly increased to the peak at nearly 40 kW and decreased thereafter. It demonstrated that a real relationship was existent among the M.I. the amount of β phase and the static oxidation behavior of plasma sprayed MoSi2 based coatings. Both too low and too high M.I. accelerated the failure of the protective coatings. The excellent oxidation resistance could only be achieved by having a proper M.I. and the highest β amount in the sprayed coating.