Synthesis and characterization of a high-strength alumina ceramic reinforced by AlN-Al₂O₃ coating

In this study, a high-strength alumina ceramic reinforced by a coating composed of 25wt% AlN and 75 wt% Al₂O₃ (labeled as ACRA-CoA) was fabricated using the spark plasma sintering (SPS) method. The thermal expansion coefficient difference between the coating and the substrate generates significant residual compressive stress in the coating during sintering cooling process, which acts protectively on the ceramic substrate, hindering crack propagation and enhancing mechanical strength. As a result, ACRA-CoA demonstrates an impressive flexural strength of 586.4 ± 70.5 MPa, marking a substantial 65.7% increase compared to conventional alumina's strength of 353.9 ± 20.5 MPa. Additionally, the doped aluminium nitride in the coating significantly improves its thermal properties, for example, at 25 °C, the thermal conductivity of ACRA-CoA is 28.93 W∙m − ¹ ∙K − ¹, which is 46.2% higher than that of conventional alumina, and the thermal diffusion coefficient increased by 43.5% to 0.089 mm − ² ∙S − ¹, while the coefficient of thermal expansion is 8.5 × 10 − ⁶ K − ¹