The basic trait in the ceramics is their high brittle or low fracture toughness, and the main criteria in the design and application is specifying the fracture toughness in ceramics. In this paper, a new method is proposed to determine the fracture toughness of ceramics, which is enhanced in lowering the cost of fracture toughness determination relative to the previous methods. Hence due to the low cost and case of access of alumina (Al2O3) which is extensively used in ceramics industry, it is applied as the most important source for achieving the objectives. Pure alumina has excellent properties such as refractory and high hardness on one hand, and has disadvantages such as low fracture toughness on the other hand. In order to improve its mechanical properties, various additives such as nano scale silicon carbide (SiC) powder are used. In this paper, alumina micro powder having 5% nano magnesium oxide by weight were mixed separately with silicon carbide nano particles of 2.5%, 5%, 7.5%, 10% and 15% to construct various types of ceramics, with different physical and mechanical properties. Semi experimental equation for their fracture toughness determination was presented and used for other brittle materials. This equation has minimal cost of experiments for determining fracture toughness of different brittle materials. Manuscript profile

Abstract: In this study, Al2O3–SiC nanocomposites have been fabricated by mixing of alumina powder containing 0.05% weight magnesium oxide and silicon carbide nano powders, followed by hot pressing at 16500C. The mechanical properties of Al2O3-SiC nanocomposites containing different volume fraction (2.5, 5, 7.5, 10 and 15%) of nano scale SiC particles were investigated and compared with those of alumina. The MgO additive was able to promote the densification of the nanocomposites. Al2O3-SiC powders were prepared by planetary milling in isopropanol. The fracture mode and microstructure of specimens was investigated by means of scanning electron microscopy. The nanocomposites were tougher compared to alumina when they were hot pressed at the same temperature. The young’s modulus is decreased by increasing the volume percent of SiC. The values hardness and fracture toughness of the nanocomposites is increased by increasing the volume percent of SiC up to 7.5% and then decreased slightly. The ballistic energy dissipation ability is decreased by increasing the volume percent of SiC up to 5% and then increased slightly. The Scanning electron microscopy observations showed that fracture mode is changed from intergranular for alumina to transgranular for nanocomposites. It also shows the growth of grain is decreased by increasing the volume fraction of SiC particles. Finally X-ray diffraction analysis indicated that there was no chemical reaction between Al2O3 and SiC particles. Manuscript profile