原位增韧SiC-YAG复相陶瓷的致密化

Densification of in-situ Toughened SiC-YAG Composites

以β-ＳｉＣ粉加入少量作为晶种的α-ＳｉＣ为起始原料，通过高温热处理过程中的相变和长柱状晶粒生长来制备原位增韧ＳｉＣ基复相陶瓷；调整埋烧工艺控制高温热处理过程中液相挥发和保持稳定的化学计量比，以保证液相全部晶化为ＹＡＧ相，着重解决了长柱状晶粒生长过程中的致密化．发现在完全形成紧密的网络状结构之前，长柱状晶粒的形成可能延缓致密化速率，但不会由此中止致密化过程．通过调整热处理条件，制备得到了完全致密化（＞９９％理论密度）并具有优异断裂韧性（Ｋ１ｃ＝６．９ＭＰａｍ１／２，ＳＥＰＢ法）的原位增韧ＳｉＣ－ＹＡＧ复相陶瓷．

Densification, a phase transformation, elongated SiC grain growth and microstructure,and mechanical properties, especially toughness, of in--situ toughened SiC-YAG composites wereinvestigated in detail. By using packing powders with same compositions as packed samples, theevaporation of Al2O3 was inhibited and full densification (>99% of theoretical density) of in-situtoughened SiC-YAG was achieved. The phase transformation occurrs at 1950, however,remained SiC can be still found by XRD after post-heated at 2100 for 4h. The content ofliquid phase and a-SiC seeds has no effect on the phase transformation rate. Following phasetransformation and grain growth during post-heating, further densification of in-situ SiC-YAGcontinues and the network microstructure consisting of elongated SiC grains can be obtained.Finally, the SEPB fracture toughness achieved is near 7.0 MPa.m1/2.