Thermal Conductivity of AlN/Diamond Composites Sintered under High-Pressure and High-Temperature

Aluminum nitride (AlN) ceramics are important heat-dissipation materials for high-power electronic devices. However, the high sintering temperature required by conventional processing routes limits practical application of AlN ceramics and increases fabrication costs. Therefore, it is necessary to develop preparation method that is capable of achieving densification at relatively low temperature. To address the difficulty of simultaneously obtaining high densification and high thermal conductivity in polycrystalline AlN ceramics under reduced-temperature sintering conditions, this work adopts a stepwise research strategy. First, the densification behavior and thermal conductivity of pure AlN under high-pressure assistance were investigated to identify the optimal sintering conditions. Under additive-free conditions, pure-phase AlN ceramics with clean grain boundaries and high densification were prepared at 5.0 GPa and 1400 ℃, achieving a thermal conductivity of 101.6 W/(m·K). Based on these optimized conditions, the AlN/diamond composite system was further studied, and the effects of diamond volume fraction on the structure and properties of the composites were systematically examined. The results show that the thermal conductivity of the composites first decreases and then increases with increasing diamond volume fraction, reaching 112.4 W/(m·K) at 33.3%. Mechanistic analysis indicates that interfacial thermal resistance dominates at low diamond contents, whereas at high diamond contents the enhancement of heat transport by thermally conductive diamond pathways becomes more significant. By taking full advantage of the processing benefits of high-temperature and high-pressure technology, this work achieves substantial improvement of AlN-based materials at temperatures lower than those required in conventional sintering, thereby providing a new route for the low-temperature fabrication of high-performance thermally conductive ceramics.