Inhibition of the formation of the B metastable phase in yttrium oxide plasma-spray coatings by the addition of zirconia
V. GOURLAOUEN, G. SCHNEDECKER, M. BONCOEUR
JOURNAL OF MATERIALS SCIENCE
ABSTRACT:Yttrium oxide plasma-spray deposits show a metastable B phase together with the cubic stable form. This B form is prejudicial for thermal applications of these coatings (i.e. weakens mechanical properties, etc.). Attempts have been made to avoid the formation of this metastable phase during the plasma-spraying operation by use of an inhibitor, such as Zr02. A large solid solution with cubic C phase was found to form between Zr02 and Y203 (Y1-xZrxOl.~+x/zC3o.5-x/2). A method is described for preparing powders suitable for plasma spraying. Several compositions were tested. B phase is no longer formed for ZrO2 additions as low as x = 0.03. The influence of Zr02 addition on Y203 coatings properties is discussed.
Key words:metastable phase; plasma spraying; plasma-spraying; stable form
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