Fabrication Of Al₂O₃/Cr₃C₂ Composite Ceramic Material And Its Performance

The alumina ceramic has excellent hardness, wear resistance, high-temperature erosion resistance, corrosion resistance, small density and wide raw materials, but the intrinsic fragility limits its wide application. Exploiting an effective approach to improve the mechanical properties of the alumina ceramic, especially its fracture toughness and flexural strength, will be significant for widening the actual application, as well as for the theoretical value. Due to the high modulus, high thermal expansion coefficient, high-temperature erosion resistance of Cr₃C₂, and the high modulus, high-temperature erosion resistance of (W,Ti)C, SiC and Ti(C,N), novel composition systems of multiphase ceramic materials Al₂O₃/Cr₃C₂/(W,Ti)C, Al₂O₃/Cr₃C₂/Ti(C,N), Al₂O₃/Cr₃C2/SiC have been suggested in this thesis, designated as ACW, ACT, ACS, respectively. The HP sintering technology, mechanical properties, microstructure, toughening mechanism, properties of wear and corrosion resistance, thermal shock resistance, and the fundamental application have been studied.Based on the residual stress toughening and the grain refining toughening mechanisms, the dispersed particulates Cr₃C₂ with (W,Ti)C, or SiC, Ti(C,N) are designed to toughen the ceramic Al₂O₃.A novel method is devised for measuring the density of ceramic specimen with high efficiency based on the Archimedes method.Composite ACW, ACT, ACS ceramic materials have been developed successfully by the HP sintering with N₂ atmosphere. A flexural strength of 562MPa, a fracture toughness of 9.35MPa·m^1/2 and a hardness of 18.77GPa are obtained for ACW. A flexural strength of 715MPa, a fracture toughness of 8.58MPa·m^1/2 and a hardness of 20.9GPa are obtained for ACT. A flexural strength of 515MPa, a fracture toughness of 8.22MPa·m^1/2 and a hardness of 18.19GPa are obtained for ACS. Microstructure investigation of the 3 composite ceramic materials by means of SEM, TEM, EDAX, and SAD, shows that excellent microstructure could be obtained only with the condition of the suitable HP sintering technique and the suitable volume fraction. Many dislocations, intragranular particles, and some thermal strain streaks were found inside the microstructure of the 3 investigated composites, which improve the mechanical properties of the materials. The second phase paniculate at the grain boundary inserts a dragging force to retard the migration of grain boundary, and restrains the growth of the matrix grain to obtain fine microstructure. Not only the intragranular fracture mode but also the intergranular mode could be found in the rough bending fracture sections of the...