Structural characteristics of the formation of double-layer plasma-sprayed coatings

1. A study was made with the aim of examining the structural characteristics of the formation of double-layer (tungsten-zirconia) plasma-sprayed coatings on Kh18N10T steel and OT4 titanium alloy substrates. 2. It is shown that the high thermal stresses set up during the spray-deposition of zirconia result in microcrack formation in the tungsten undercoat. When the deposition is performed at high values of power supplied, tungsten oxidation products appear at the interface between the two coatings. 3. The application of zirconia coatings is accompanied by the recrystallization of austenitic grains in the stainless steel substrate and polymorphic transformation in the titanium alloy substrate. 4. The microhardness and the size of the increased-microhardness zone (in the presence of the double-layer coating) decrease, as a result of recrystallization, for the Kh18N10T steel substrate and slightly increase for the titanium substrate. 5. A change in technique in the deposition of the tungsten undercoat, resulting in a decrease in the latter's thickness, is accompanied by a tell-tale increase in grain size in the substrate. 6. The optimum conditions for the spray-deposition of zirconia have been determined.