Controlling the flaw size and mechanical properties of ZTM/SiCp composites

Ultrafine mullite and zirconia powders were prepared by sol-gel and precipitation processes, then mixed homogeneously with mu m-sized silicon carbide particles (SiCp) to obtain composite powder. A dense green body with homogeneous microstructure was prepared by the pressure filtration technique. After being dried carefully, the green body was hot-pressed under different conditions to optimize its microstructure. The effect of different hot-pressing conditions on the mechanical properties was investigated and the hot-forging effect was also taken into account. It was found that the strength of the composite was greatly increased, from about 600 MPa reported to 810 MPa at room temperature and 830 MPa at 1000 degrees C, under the conditions of moderately low hot-pressing temperature and long holding time, while the fracture toughness of the composite remained almost unchanged. From this it was shown that the control of strength-limiting processing defects was effective. Because of the homogenous microstructure improved during forming and optimized during sintering and a combination of various strengthening mechanisms, it was possible to enhance the strength of the composite significantly. (C) 1996 Elsevier Science Limited