Preparation of Si-Al-Zr-O Composite Ceramics with Ultra Fine Grains by in situ Controlled Crystallizing from the Amorphous Bulk

The homogeneous SiO2-Al2O3-ZrO2(SAZ) sol was prepared at 1650- 1700℃and transparent amorphous bulk was obtained by controlling the cooling process. The bulk was treated at 950℃for 2h to nucleate and at 1100- 1250℃for 1h to crystallize, and SAZ composite ceramics with ultra fine grains were prepared. The effects of heat treatment on the structure and properties of the composite caramics were analyzed by using DSC, IR, XRD, SEM and Vickers indentation techniques. The results show that crystallization of SAZ amorphous bulk begins with t-ZrO2 at about 950℃and completes at about 1100℃. The main phases are mullite, t-ZrO2. With the increase of crystallization temperatures, the gains grow rapidly from 10~40nm to 0.5μm, and the transformation of zirconia from tetragonal into monoclinic occurs. The values of microhardness and fracture toughness are largest at 1150℃, those are 12.6GPa and 4.32MPa·m1/2 respectively.