Phase composition and stability of nanostructured 4.7 wt.% yttria-stabilized zirconia coatings deposited by atmospheric plasma spraying

Phase composition and stability of plasma-sprayed nanostructured 4.7 wt.% Y2O3-stabilized zirconia coatings were investigated by using X-ray diffraction (XRD) and Raman spectroscopy. The nanostructured as-sprayed coatings consisted of a nontransformable tetragonal phase (T′ phase) and an orthorhombic phase. The T′ phase decomposed into the low-yttria and high-yttria tetragonal phases when the annealing temperature was above 1200 °C. The orthorhombic phase observed during annealing resulted from the fast densification of the as-sprayed coating. It acted as an intermediate phase of the transformation of the low-yttria tetragonal to a monoclinic phase during cooling. The orthorhombic phase quickly decreased when the transformation spontaneously occurred due to the grain size being larger than the critical size.