Tri-layer Si/mullite/Yb₂SiO₅ environmental barrier coating (EBC) was prepared on the SiCf/SiC ceramic matrix composite (CMC) by plasma spray-physical vapor deposition (PS-PVD). The EBC samples were carried out with water vapor corrosion at 1300 °C for 200 h. After steam corrosion, Yb₂SiO₅ layer forms a gradient porous structure. This is mainly due to the inclusion of SiO₂-rich layer which is precipitated from the gasification inside the coating and existing a small amount of Yb₂O₃ separately. During the corrosion process, water vapor infiltrates into the coating and reacts with the SiO₂ and Yb₂O₃ to generate volatile substances. This forms a porous structure to make the coating brittle, resulting in mud cracks finally. In addition, the results show that the Yb₂SiO₅ can react with the water vapor at the coating surface, forming an Yb₂Si₂O₇ top layer.

The deposition of photocatalytic TiO₂ coatings with plasma spraying is attractive for large-scale applications due to its low cost and simplicity, but it is still a challenge to obtain a TiO₂ coating with high anatase content. The solidification pathway of inflight melted particles was investigated in the present paper, and TiO₂ coatings with enhanced photocatalytic activity were obtained without a significant loss of the microhardness. The coating microstructure, phase composition, and crystallite size were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Photocatalytic performance was evaluated by decomposing an aqueous solution of methylene blue. Results showed that the anatase content in TiO₂ coating was augmented to 19.9% from 4%, and the time constant of the activity was increased to 0.0046 h⁻¹ from 0.0017 h⁻¹.

The air-plasma-sprayed ceria and yttria-stabilized zirconia (CYSZ) coating was modified by selective laser remelting and Al deposition to enhance hot corrosion resistance. The dotted coating was obtained after selective laser remelting. Magnetron sputtering was used to deposit an Al film on the dotted coating, and a vacuum heat treatment was subsequently performed to produce a dense α-Al₂O₃ overlay. Hot corrosion behavior of the following three types of coatings was investigated: plasma-sprayed, dotted, and dotted coatings combined with Al deposition (DA). Hot corrosion behaviors were evaluated in a mixture of 55 wt % V₂O₅ and 45 wt % Na₂SO₄ molten salts at 1000 °C for 30 h. The hot corrosion reaction between molten salts and zirconia stabilizers (Y₂O₃ and CeO₂) led to the generation of monoclinic zirconia, YVO₄, and CeVO₄ plate-shaped crystals, and the mineralization of CeO₂. The results indicated that the hot corrosion resistance of the DA coating was the best, and the dotted coating had superior hot corrosion resistance in comparison with the plasma-sprayed coating. The minimal surface roughness and dense dotted units improved the hot corrosion resistance of the dotted coating. The dense α-Al₂O₃ overlay with chemical inertness effectively inhibited the infiltration of molten salts, which led to the optimal hot corrosion resistance of the DA coating.

Nano-indentation is a popular method to characterize the micromechanical properties of nanostructured 8YSZ coatings. However, little research has focused on the creep behavior of nano-indentation and only the elastic modulus and nanohardness have been analyzed. Herein, for the first time, the nano-indentation creep behavior of plasma-sprayed nanostructured 8YSZ coatings using as-prepared nanostructured non-transformable tetragonal (t’) feedstocks was investigated. The indentation creep behavior can be well characterized by the power-law equation and the strain rate sensitivity has been calculated in light of the equation. The strain rate sensitivity was sensitive to the load and the reasons were analyzed in detail. The current results can further guide and design thermal barrier coatings from the point of indentation creep property.