Ceramic thermal-barrier coatings on hot engine parts have the potential to reduce metal tempera¬tures, coolant requirements, cost, and complexity of the cooling configuration, and to increase life, turbine efficiency and gas temperature. Coating systems consisting of a plasma-sprayed layer of zirconia stabilized with either yttria, magnesia or calcia over a thin alloy bond coat have been de¬veloped, their potential analyzed and their dura¬bility and benefits evaluated in a turbojet engine. The coatings on air-cooled rotating blades were in good condition after completing as many as 500 two-minute cycles of engine operation between full power at a gas temperature of 1644 K and flameout, or as much as 150 hours of steady-state operation on cooled vanes and blades at gas temperatures as high as 1644 K with 35 start and stop cycles. OB the basis of durability and processing cost, the yttria-stabilized zirconia was considered the best of the three coatings investigated.
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