Phase transformation and wear studies of plasma sprayed yttria stabilized zirconia coatings containing various mol% of yttria

Plasma sprayable grade zirconia powders doped with various mol% of yttria (0, 2, 3, 4, 6, 8 and 12 mol%) were synthesized by a chemical co-precipitation route. The coprecipitation conditions were adjusted such that the powders possessed good flowability in the as calcined condition and thus avoiding the agglomeration step like spray drying. Identical plasma spray parameters were used for plasma spraying all the powders on stainless steel plates. The powders and plasma sprayed coatings were characterized by X-ray diffractometry, Scanning Electron Microscopy and Raman spectroscopy. Zirconia powders are susceptible to phase transformations when subjected to very high temperatures during plasma spraying and XRD is insensitive to the presence of some non crystalline phases and hence Raman spectroscopy was used as an important tool. The microstructure of the plasma sprayed coatings showed a bimodal distribution containing fully melted and unmelted zones. The microhardness and wear resistance of the plasma sprayed coatings were determined. Among the plasma sprayed coatings, 3 mol% yttria stabilized zirconia coating containing pure tetragonal zirconia showed the highest wear resistance.

Research Highlights
► Preparation plasma sprayable YSZ powders without any agglomeration process and plasma spraying
► Phase transformation studies of plasma sprayed YSZ coatings by XRD and Raman spectroscopy
► Microstructure of the plasma sprayed coatings exhibited bimodal distribution
► Plasma sprayed 3 mol% YSZ coating exhibited the highest wear resistance
► Higher wear resistance is due to the higher fracture toughness of tetragonal 3 mol% YSZ phase