REACTIVE PLASMA SPRAYING OF MOSI2 USING AN AR-10-PERCENT-CH4 POWDER CARRIER GAS

Plasma spraying of MoSi2 using an Ar-10%CH4 powder carrier gas mixture was investigated as a way of incorporating carbon and carbide particles into spray deposits of MoSi2 which could subsequently getter SiO2 after elevated-temperature exposure. After hot isostatic pressing (HIP) at 1800-degrees-C and 200 MPa for 1 h a decrease in oxygen from approximately 2580 to 750 ppm resulted in the spray deposits of MoSi2 produced with the Ar-CH4 powder gas carrier. A factor of 3 increase in yield strength was observed in these deposits when compared to conventional hot-pressed MoSi2 at temperatures between 1100 and 1400-degrees-C. This increase was attributed to a decrease in SiO2 in the MoSi2 matrix. The presence of SiC particles was identified in as-sprayed deposits of MoSi2 and after HIP. Silicon carbide particles in the as-sprayed condition resulted from inflight reactions between MoSi2 and carbon present in the methane gas. Spray deposits of MoSi2, without the use of the Ar-CH4 powder carrier gas, were also produced in order to establish a baseline in elevated temperature behavior.