Investigation of the silicon loss in APS MoSi{sub 2} under the range of typical spray conditions

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MoSi{sub 2} provides good high temperature oxidation and corrosion resistance. However, the lower silicides such as Mo{sub 5}Si{sub 3} do not provide such resistance. In this study, air plasma sprayed (APS) MoSi{sub 2} particle temperatures and velocities were measured under various torch conditions chosen to span the majority of typically utilized spray parameters. Empirical models of particle temperature and velocity were computed from the data. Three spray conditions were chosen to produce high, medium and low particle temperature and velocities. Coatings produced under these spray conditions were characterized by profile tracing, quantitative x-ray diffraction, and SEM analysis. The Mo{sub 5}Si{sub 3} level in the coatings ranged from 5% to 8% while the Mo{sub 5}Si{sub 3} level in the starting powder was 0.6%. Particle size, particle trajectory, and torch parameters were found to be important factors in the Si loss process when APS depositing MoSi{sub 2}.