Thermal stability studies of plasma sprayed yttrium oxide coatings deposited on pure tantalum substrate

Plasma sprayed Yttrium oxide is used for coating of crucibles and moulds that are used at high temperature to handle highly reactive molten metals like uranium, titanium, chromium, and beryllium. The alloy bond layer is severely attacked by the molten metal. This commonly used layer contributes to the impurity addition to the pure liquid metal. Yttrium oxide was deposited on tantalum substrates (25 mm x 10mm x 1mm thk and 40 mm x 8mm x 1mm thk) by atmospheric plasma spray technique with out any bond coat using optimized coating parameters. Resistance to thermal shock was evaluated by subjecting the coated specimens, to controlled heating and cooling cycles between 300K to 1600K in an induction furnace in argon atmosphere having <= 0.1ppm of oxygen. The experiments were designed to examine the sample tokens by both destructive and non-destructive techniques, after a pre-determined number of thermal cycles. The results upto 24 thermal cycles of 25 mm x 10mm x 1mm thk coupons and upto 6 cycles of 40 mm x 8mm x 1mm thk coupons are discussed. The coatings produced with the optimized parameters were found to exhibit excellent thermal shock resistance.