INHIBITION OF THE FORMATION OF THE B-METASTABLE PHASE IN YTTRIUM-OXIDE PLASMA-SPRAY COATINGS BY THE ADDITION OF ZIRCONIA

Yttrium oxide plasma-spray deposits show a metastable B phase together with the cubic stable form. This B form is prejudicial for thermal ap plications of these coatings (i.e. weakens mechanical properties, etc. ). Attempts have been made to avoid the formation of this metastable p hase during the plasma-spraying operation by use of an inhibitor, such as ZrO2. A large solid solution with cubic C phase was found to form between ZrO2 and Y2O3 (Y1-xZrxO1.5+x/2 square 0.5-x/2). A method is de scribed for preparing powders suitable for plasma spraying. Several co mpositions were tested. B phase is no longer formed for ZrO2 additions as low as x = 0.03. The influence of ZrO2 addition on Y2O3 coatings p roperties is discussed.