The influence of different SiC amounts on the microstructure, densification, and mechanical properties of hot-pressed Al2O3-SiC composites

The hot pressing process of monolithic Al2O3 and Al2O3-SiC composites with 0-25 wt% of submicrometer silicon carbide was done in this paper. The presence of SiC particles prohibited the grain growth of the Al2O3 matrix during sintering at the temperatures of 1450 degrees C and 1550 degrees C for 1 h and under the pressure of 30 MPa in vacuum. The effect of SiC reinforcement on the mechanical properties of composite specimens like fracture toughness, flexural strength, and hardness was discussed. The results showed that the maximum values of fracture toughness (5.9 +/- 0.5 MPa.m(1/2)) and hardness (20.8 +/- 0.4 GPa) were obtained for the Al2O3-5 wt% SiC composite specimens. The significant improvement in fracture toughness of composite specimens in comparison with the monolithic alumina (3.1 +/- 0.4 MPa.m(1/2)) could be attributed to crack deflection as one of the toughening mechanisms with regard to the presence of SiC particles. In addition, the flexural strength was improved by increasing SiC value up to 25 wt% and reached 395 +/- 1.4 MPa. The scanning electron microscopy (SEM) observations verified that the increasing of flexural strength was related to the fine-grained microstructure.