Simulation Study On Microstructure Of Nano-composite Ceramic Tool Materials By Phase-field Method

Ceramic tools have greater advantages such as thermal-resistance, wear-resistance and chemical stability than conventional tools in high speed cutting and machining difficult-to-cut materials. But the development method of ceramic tool materials is a "trial-error method", so that the development process of new ceramic tool materials is very long and need high cost. The computer simulation of microstructure for nano-composite ceramic tool materials can guide the development of new ceramic tool materials and reduce the development time. Compared to the traditional simulation methods, the phase-field simulation of microstructure has obvious advantages, it has become an international hotspot research field. Consequently, the phase-field simulation of microstructure for nano-composite ceramic tool materials during the fabrication is researched in the thesis.On the basis of the analysis of grain growth theories, the two-dimensional Phase-field simulation models of microstructure for ceramic tool materials have been established. Two-dimensional simulation software of microstructure for ceramic tool materials has been developed on the basis of Microsoft Visual C++ 6.0 compiler, using C++ language and the OpenGL graphics interface. The developed software in the present thesis can accomplish the two-dimensional simulation of microstructure for ceramic tool materials during fabrication, the outputs of two-dimensional simulation results and simulation data at any simulation time.The phase-field simulation model of microstructure for single-phase ceramic tool materials without defects has been established and simulated. The effect of simulation time and fabrication temperature on the grain growth of ceramic tool materials has been discussed. It is shown that mean grain radius increases by the way of parabola with an increment in simulation time, and mean grain radius and grain growth rate also increases with an increment in fabrication temperature.The phase-field simulation model of microstructure for two-phase ceramic tool materials without defects has been established and simulated. It is shown that the mean grain area decreases with an increment in the content of the second particles, and the grain size is becoming homogeneous and the grains tend to concentrate on the trijunction of grains. The smaller grains can inhibit the matrix grain from growing and generate pinning-effect which will become stronger with an increment in the content of the second particles.The phase-field simulation model of microstructure for single-phase ceramic tool materials containing pores has been established and simulated. It is shown that the pores in the materials play an important role in inhabiting the grain growth. During the same simulation time, the mean grain radius of the ceramic tool materials without pores is bigger than that of the materials containing pores. The phase-field simulation model of microstructure for two-phase ceramic tool materials containing pores has been also established and simulated. It is shown that the grain growth rate of two-phase ceramic tool materials containing pores is slower than that of single-phase ceramic tool materials containing pores due to the combined inhibiting effect of pores and second-phase particles. With the increment of simulation time and the densification, the inhibiting effect by pores will reduce, so the grain growth rate of single-phase ceramic tool materials becomes bigger and the grain growth rate of two-phase ceramic tool materials is almost unaffected due to the pinning effect of the second-phase particles.