Effect of nano-sized SiC and micro-sized YAG dispersion on the microstructure of alumina

Alumina-based ceramic composites prepared by participate dispersion using SiC and Y₂O₃ as additives were studied under hot-pressing at 1400 to 1600°C for 0 to 20h. An yttrium aluminum garnet (YAG, Y₃Al₅O₁₂) phase was formed by the reaction between Al₂O₃ and Y₂O₃ above at 1400°C after 10 min of hot-pressing, and dense Al₂O₃/5 vol%SiC/20 vol%YAG composites resulted. The YAG phase was dispersed at the grain boundary of the Al₂O₃ matrix with equiaxed grains. Fine SiC was dispersed uniformly within the Al₂O₃ matrix, whereas coarse SiC particulates, which showed stacking faults, were located in the grain boundaries between the Al₂O₃ and YAG. The YAG phase was bonded directly to the Al₂O₃. An impurity phase, which apparently was amorphous, could be detected at the interface between the Al₂O₃ and SiC. The grain size of the monolithic Al₂O₃ increased remarkably with increases in hot-pressing temperature and time; grain growth in the Al₂O₃/SiC/YAG composites were effectively restrained, and those samples exhibited a narrower grain size distribution. This uniformly fine microstructure could be attributed to the incorporation of the YAG and SiC particulates, because of grain boundary pinning by the particulates.