Enhancing High-Temperature Strength and Thermal Stability of Al2O3/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-Al2O3at 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 A1 powders.It was found that the pre-treatment at ≤550℃ could introduce a few Al2O3in 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℃,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(AIN+γ-Al2O3)/Al exhibited more superior thermal stability compared to amAl2O3/Al for annealing treatment at 580℃ for 8 h.Therefore,an effective way to fabricate high-temperature Al composite with enhanced thermal stability was developed in this study.