Conditions of formation and inhibition of a metastable phase in Y(sub 2) O(sub 3) plasma spray coatings

摘要

Plasma spray technique is used to obtain yttrium oxide coatings. Structural investigation of such deposits shows that a minor monoclinic B phase is present close to the cubic C stable form. The influence of different spraying parameters (velocity, distance) on the formation of the B phase is examined and the main properties of such materials determined. The B modification is metastable and thus detrimental for thermal applications of the coating (i.e. mechanical properties) owing to the increase in volume resulting from the B to C transition. Using Zr O(sub 2) as stabilizing agent in the starting powder has been tried in order to avoid the B variety formation during the plasma spraying operation. In this case, deposits are only constituted by the C form with good thermal behaviour. (from authors) 3 figs., 2 tabs., 4 refs.