Microstructure Formation Mechanism of (Al_2O_3+TiB_2+Al_3Ti)/Al Composites Fabricated by Reactive Hot Pressing

摘要

The two (Al_2O_3+TiB_2+Al_3Ti)/Al composites were fabricated from Al-B_2O_3-TiO_2 and Al-B-TiO_2 raw powders by reactive hot pressing, respectively. The microstructure of in situ two composites was analyzed by OM, SEM and TEM. The results showed that coarse Al_3Ti blocks with several tens of micrometers size were formed during hot pressing. The equiaxed Al_2O_3 particulates and hexagonal TiB_2 particulates with finer sizes were formed in the composites simultaneously. The microstructure formation mechanism of (Al_2O_3+TiB_2+Al_3Ti)/Al composites were discussed. The results showed that Al_2O_3 reinforcements were formed on the surface of TiO_2 or B_2O_3 powder and TiB_2 particles were formed on B or B_2O_3 powders. The formation of coarse Al_3Ti block is result from continuous diffusion of Ti in liquid Al during reactive hot pressing. In addition, there are fine Al_3Ti precipitates exist in the composite fabricated from Al-B-TiCO_2 powders. This contributes to the improved mechanical properties in terms of yield and ultimate stresses and Young's modulus of the composite.