In this paper, induction plasma spray processing is used to produce free-standing-parts of molybdenum silicide-B composition, the boron, and molybdenum silicide powders being blended to form the initial spray powders. The oxidation resistance for each of these composites is compared to those of molybdenum silicide and molybdenum disilicide plasma spray deposits, produced under identical conditions. The results indicated that the 2.0 wt% boron sample had excellent oxidation resistance and showed a mass change of almost zero after 24 hours of high temperature oxidation (1210 deg C). Paper includes a German-language abstract.

This study was aimed at the production of SiC-MoSi2 composite powders through a high-temperature plasma reaction route. The addition of SiC appears to be the best second phase reinforcement for improving the mechanical properties of MoSi2 material for high-temperature structural application. The in-flight carbonization of MoSi2 powders was carried out in an Ar-H2-CH4 induction plasma process. Using methane served as both the powder carrier gas and the "precursor" to react with the MoSi2 powders forming the SiC phase in-situ . Under the experimental conditions employed in this investigation, up to about 8.0 wt. % of carbon was incorporated into the MoSi2 powder particles. The chemical composition, phase content and the microstructure of the composite powder products were examined by XRD, SEM, EDS etc. analysis methods. The reaction mechanisms are discussed in terms of the calculated thermodynamic equilibria.

The in-flight modification of MoSi 2 powders has been carried out by using an Ar-H 2 induction plasma. Reactor pressure, powder feed rate and plate power level were taken as the experimental parameters to alter the thermal history of the injected powder particles. Metastable hexagonal structure of P-MoSi 2 is the major phase observed in the induction plasma treated molybdenum disilicide powders, the stable phase of tetragonal structure of α-MoSi 2 usually retains approximately 30 wt.%. Following the change in experimental condition and the deviation from stoichiometry in raw materials, low silicides, Mo 5 Si 3 and Mo 3 Si, and free Si were observed. The formation of these phases are explained in terms of metastable eutectic reaction during rapid solidification processing. The relationship between the quantities of all these phases and the experimental conditions has been discussed.