Enhancing High-Temperature Strength and Thermal Stability of Al_2O_3/Al Composites by High-Temperature Pre-treatment of Ultrafine Al Powders

Amorphous Al₂O₃-reinforced Al composite (am-Al₂O₃/Al) compacted from ultrafine Al powders for high-temperature usages confronts with drawbacks because crystallization of am-Al₂O₃ at high temperatures will result in serious strength loss. Aiming at this unsolved problem, in this study, high-temperature Al materials with enhanced thermal stability were developed through introducing more thermally stable nano-sized particles via high-temperature pre-treatment of ultrafine Al powders. It was found that the pre-treatment at ≤ 550 °C could introduce a few Al₂O₃ in the Al matrix and increase the strength of the composites, but the strength was still below that of am-Al₂O₃/Al because without being pinned firmly, grain boundaries (GBs) were softened at high temperature and intergranular fracture happened. When the pre-treatment was carried out at 600 °C, nitridation and oxidation processes happened simultaneously, producing large numbers of intergranular (AlN + γ-Al₂O₃) particles. GB sliding and intergranular fracture were suppressed; therefore, higher strength than that of am-Al₂O₃/Al was realized. Furthermore, the (AlN + γ-Al₂O₃)/Al exhibited more superior thermal stability compared to am-Al₂O₃/Al for annealing treatment at 580 °C for 8 h. Therefore, an effective way to fabricate high-temperature Al composite with enhanced thermal stability was developed in this study.