Sintering of Silicon Carbide Ceramics with Co-addition of Gadrinium Oxide and Silica and Their Mechanical Properties

摘要

Effects of simultaneous addition of SiO_2 and gadrinium oxide on densification of SiC ceramics were examined, and relation between microstructure and their mechanical properties were discussed. Total 11 wt% of Gd_2O_3 and SiO_2 were mixed with fine β-SiC powder. The weight of Gd_2O_3 in (Gd_2O_3 + SiO_2) were set as 0, 20, 40, 60, 80 and 100%. The mixture was hot-pressed at 1950℃ under 40 MPa applied pressure for 1 h. In the case of 40Gd_2O_3 and 80Gd_2O_3 compositions, the effect of sintering temperature from 1900 to 2000℃ was also examined. The bulk density increased with increasing Gd_2O_3 content at the sintering temperature of 1950℃. Bending strength of the sintered bodies also improved with increasing Gd_2O_3 content generally, but at 40Gd_2O_3 composition, the maximum over ～800 MPa was observed. Young's modulous, Vickers hardness and fracture toughness also increased with increasing Gd_2O_3 content. The distribution of grain boundary phase was not homogeneous. Evaporation of additives, mainly SiO_2, caused non-homogeneous distribution of grain boundary phase between outside and inside of sintered bodies. High temperature bending strength of 80Gd_2O_3 specimen was superior than that of 40Gd_2O_3 specimen.