METHOD AND APPARATUS FOR DEPOSITING STABLE CRYSTALLINE PHASE COATINGS OF HIGH TEMPERATURE CERAMICS

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Producing high temperature coatings on ceramics using a high enthalpy air plasma spray torch and supplying in at least 3 passes to deposit the coating is advantageous for spraying high temperature ceramics while avoiding formation of undesirable phases, if the stand off distance is chosen such that a width of a bead produced from a single spray pass on the substrate at ~800°C is less than 70% of a diameter of a plume of the torch at the stand off, and neither assisted heating, nor forced cooling, nor subsequent heat treatment is used. The rapid cooling endemic to thermal spray that leads to amorphous, metastable and other undesirable phases of alkaline earth aluminosilicate (e.g., barium- strontium aluminosilicate (BSAS)), rare earth silicates (RESs), mullite, etc. can be mitigated sufficiently by the close stand off and high enthalpy torch to provide highly crystalline and stable phase coatings.