Abstract

Plasma sprayed bondcoats of MCrAIY type play a dominant role for the life of thermal barrier coatings. During service an oxide is formed between the bond and top coat, also internally and between the bond coat and the substrate. This oxide growth has to be minimised to improve the coating's life. Apart from the powder chemistry, the coating microstructure is the major factor governing the oxidation in a given environment. It is known that the coating microstructure and the coating strength are strongly related to the plasma spraying parameters. In this work, the effects of the in flight particle properties on the adhesion/cohesion and on the microstructure of a NiCrAIY & NiCoCrAIY bond coat are investigated. The relation between the particle velocity and temperature, as measured with the DPV 2000 particle diagnostic system, and the coating properties are very important. Relatively small changes of spray parameters (arc current, gas flows, ..) lead to significant changes on the sprayed particles and finally also in the coating microstructure. On the other hand, the same particle properties, although sprayed with different guns, produces coatings with similar properties. Through on-line control of the particle states it is expected that the quality of plasma sprayed MCrAIY's coatings can be significantly improved.

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