Influence of heat treatment on the lattice oxygen migration behavior, thermal and mechanical properties of AlN ceramics

This study systematically investigates the effect of heat-treatment temperature (600-1200 °C) in air on the oxidation behavior, lattice oxygen migration, and thermal and mechanical properties of AlN ceramics. The results show that when the heat-treatment temperature is ≤ 800 °C, no detectable oxide layer forms on the surface of AlN ceramics; however, lattice oxygen begins to diffuse toward grain boundaries. At 1000 °C, a continuous and dense Al 2 O 3 layer (∼2.55 μm) forms on the surface. The thermal expansion mismatch between this oxide layer and the AlN matrix induces a residual compressive stress (-749.78 MPa) in the AlN substrate. Concurrently, XPS, EDS line scanning, and hot-gas extraction collectively confirm that lattice oxygen has sufficiently migrated to grain boundary regions. The resulting lattice purification reduces phonon scattering centers, while the residual compressive stress lowers interfacial thermal resistance at grain boundaries and suppresses crack propagation. These two mechanisms act synergistically, leading to the highest flexural strength (451.48 MPa) and thermal conductivity (211.73 W·m -1 ·K -1 ) among all samples. When the temperature is further increased to 1200 °C, the oxide layer thickens sharply to approximately 30.95 μm. Cracks and pores develop due to the thermal expansion mismatch, causing a marked decrease in both thermal conductivity and flexural strength. Finally, a kinetic equation for predicting the oxide layer thickness on AlN ceramics is established based on the Hou-Chou kinetic model. A comprehensive model describing lattice oxygen migration and oxidation behavior during heat treatment is also constructed. This work provides a theoretical basis for optimizing the heat-treatment process and enhancing the performance of AlN ceramics.