Fabrication,Structure And Properties Of Al₂O₃-matrix Ceramic Composites

With the development of modern technology, traditional cutting tools have no longer been competent for various kinds of machining. Researches on Al2O3-matrix ceramics with superior mechanical properties are most significant to machining -technology.Particle-dispersing is a mostly-used method to fabricate ceramic composites. Many researches have showed that the mechanical properties of Al2O3-matrix ceramics in which Ti(C, N), TiC or TiN was dispersed could be improved a lot, which might be widely used in the field of machining. By choosing a suitable ratio to raw materials, Al2O3-matrix ceramics were fabricated by gas pressure sintering (GPS) and GPS with Post-HIP based on current techniques in this experiment.Al2O3- Ti(C, N) ceramic composite was fabricated by the proposed sintering process in this paper. By analyzing the results of X-ray diffraction (XRD) and scanning electron microscope (SEM), we could find that the densification process was controlled by the mechanism of solid phase sintering. The framework structure was formed by interleaving the crystal grains of A^Oi and TiC. This sample was mainly transgranular-fractured. The bending strength, fracture toughness and hardness were 700MPa, 5.72MPa.m12 and 19.5GPa, respectively. The mechanical properties were improved a little by the process of Post-HIP.The densification process was controlled by the mechanism of liquid phase sintering for the system of Al2O3- TiC/ TiN-ZrO2. Pores and abnormal grain growth existed in the sintered Al2O3- TiC ceramics, which caused the mechanical properties unstable. So this system could not be adopted. The TiN grains were linked tightly with the matrix of a- Al2O3 in Al2O3- TiN ceramics. This sample was also mainly transgranular-fractured. The bending strength and fracture toughness were 600MPa, 6.1MPa.m1/2, respectively. The grain size was decreased and edges were more faintness. The value of bending strength was improved to 930MPa while the fracture toughness changed little.Relationships between fabrication,structure and properties are veryimportant for studying materials. The densification mechanism and the effect of Post-HIP on the structure and properties were discussed by analyzing the mechanical properties, phase composition and microstmcture. The fabricating techniques were optimized in this approach.For applications, ceramic materials and components must be treated by surface grinding and polishing, which might induce the residual stress. The tensile residual stress, which was harmful to the performance, should be eliminated or reduced, and compressive residual stress should be introduced. In this study, the results showed that the residual stress was tensile for the specimen ground by surface grinder, while it was compressive by universal tooling grinder; polishing after grinding could smooth the residual stress. This result is important to enhance the strength and wearing of ceramic materials.These basic researches were of guidance for optimizing processing techniques, by which ceramic materials with perfect properties might be obtained.