Effects of air annealing treatments on the microstructure,components, and mechanical properties of magnetron sputtered Al2O3–Cr2O3–ZrO2 composite coatings

To investigate the effects of air annealing on the microstructure, components, and mechanical properties of ceramic composite coatings, Al₂O₃–Cr₂O₃–ZrO₂ composite coatings were prepared on silicon substrate using radio frequency magnetron sputtering at room temperature, and then air-annealed in a temperature range of 450–850 °C for 30 min. The results indicated that the phase-structure and superficial characteristics, including morphology and surface roughness, were not visibly altered in the annealed coatings up to 600 °C; the elemental component distributions remained uniform. The improvement in the mechanical properties was attributed to the growth of oxide grains. There were no significant changes in the components of Al, Cr, Zr, and O in the annealed coatings. However, an increase in the Cr component and a decrease in the Zr component occurred on the coating surface; the overall structure of the composite coatings possessed a favorable heat resistance. Upon annealing at 750 °C, the thermally-driven formation of uniform and refined nanoparticles on the coating surface was responsible for the effective enhancement of the mechanical properties. Furthermore, annealing at 850 °C induced the enlargement of the precipitated Cr₂O₃ nanoparticles and the generation of micro-defects, resulting in a drastic morphological evolution, an evident increase in the surface roughness, and a significant decrease in the mechanical properties. This study provides new perspectives on designing novel thermal barrier coatings and understanding the role of high temperature air annealing on the microstructural transformation.