Influence of liquid nitrogen quenching on the evolution of metastable phases during plasma spraying of (ZrO2–5 wt.% Y2O3)–20 wt.% Al2O3 coatings

The preparation of nanostructured (ZrO2–5 wt.% Y2O3)–20 wt.% Al2O3 coatings by atmospheric plasma spraying of commercially available micron-scale powders is reported. Materials were prepared by means of a standard spraying technique and by using an improved technique that allows for the quenching of the material using liquid nitrogen-cooled substrates. Quenching leads to the controlled formation of metastable phases. The influence of liquid nitrogen cooling on the formation of the metastable phases was studied by X-ray diffraction under a grazing incidence angle of 1°. A significant increase in the amount of the metastable zirconia phase and a more homogeneous composition along the thickness were found compared to the regularly sprayed coatings. All materials were subjected to a thermal treatment for 1 h at 1400 °C to study the evolution of stable phases.