Three Dimensional Simulation On Microstructure Evolution Of Three-phase Composite Ceramic Tool Materials

Ceramic tool material has been one of the most important cutting tool materials because of its high hardness, favorable high-temperature hardness and good wear resistance. However, the fracture toughness of ceramics is low which limits the application of ceramic tools. The appearance of nano-composite ceramic tool materials and whisker reinforced ceramic tool materials may solve the problem of low fracture toughness of ceramic materials. The mechanical properties of material are governed by the microstructure, so it is very meaningful to simulate the microstructure of nano-composite ceramic tool materials.In this paper, the three-dimensional Monte Carlo Potts model coupled with sintering parameters for microstructure evolution in three-phase ceramic tool materials and the improved simulation algorithm have been established. The simulation efficiency has been enhanced by the improved simulation algorithm owning to the function of selecting matrix grid during evolution process. Based on the Microsoft Visual C++6.0compiler, the simulation program'3DMS'has been developed using C++computational language.The effect of second-phase and third-phase nano-particles with various size and volume fraction on microstructure evolution of nano-composite ceramic tools has been simulated and researched. It is shown that the microstructure of nano-composite ceramic obtained from simulation is intra/intergranular-type. The nano-particles have inhibition effect on matrix grain growth and refine the microsturcture. With all the rest parameters equal, three-phase materials can receive better grain refining effectiveness than two-phase materials. Bigger nano-particles have weaker pinning effect than smaller ones for a specific volume fraction, and nano-particles with higher volume fraction have stronger pinning effect on matrix for a given grain size. The positions of nano-particles depend on the size and volume fraction of nano-phase. The smaller nano-particles are easier to enter into the matrix grains, whereas the larger ones prefer to locate on the grain boundaries. When the volume fraction is lower, the total pinning force is weaker, as a result the nano-particles are easier to be entrapped inside the matrix grains.The effect of grain boundary energy ratio on microstructure evolution of three-phase nano-composite ceramic tools has been simulated and researched. It is shown that, when the interfacial energy is higher than grain boundary energy, nano-particles show stronger inhibiting effect on matrix grain growth and it is easier to form intra/intergranular-type mistructure. When the interfacial energy is lower than the grain boundary energy, the nano-particles mainly locate at the grain boundaries and form an intergranular-type nano-composite ceramic material.The effect of initial particle location on microstructure evolution of three-phase nano-composite ceramic tools has been simulated and researched. It is shown that the initial particle location affects the microstructure type and grain growth process. Compared with randomly distributed nano-particles, when the particles distributed around grain boundaries initially, the mean grain size of microstructure is smaller and fewer nano-particles located inside matrix grains forming intergranular-type microstructure.The three-dimensional microstructure of three-phase nano-composite ceramic tool materials has been simulated and researched allowing for the fabrication parameters. It is shown that the average grain radius increases with an increment in sintering temperature and pressure. But the effect of sintering temperature on grain growth is bigger than that of sintering pressure. With an increase of simulation time, the mean grain radius firstly grow bigger and then almostly keep the same.The Monte Carlo Potts model for microstructure evolution in nano-composite ceramic tool materials with pores and impurities has been set up and programmed. The effect of nano-particles and pores on the microstructure evolution, grain growth and densification has been simulated and researched. It is shown that the nano-particles inhibit grain growth, and the pores affect grain growth and densification. The inhibition effect by pores is very obviously, the grain growth is slower at a lower density and vice versa. The densification of three-phase nano-composite ceramic tool material increases with an increment in simulation time, and the grain growth restrains densification.The phase-field model of defect-free three-phase composite ceramic tool materials with two kinds of nano-particles, two kinds of whiskers, whisker and nano-particles are respectively set up in this research. The function of the system free energy density has been established. The simulation program'3DPS'has been developed by FORTRAN97. The microstructure evolution of three-phase nano-composite ceramic tool materials, whisker reinforced ceramic tool materials and whisker and nano-particles toughened ceramic tool materials has been efficiently and successfully simulated. It can be found that for the whisker and particle toughened ceramic materials, whiskers with bigger radius tend to situate on the tri-grain boundaries and whiskers with smaller radius tend to stay inside matrix grains. When the length and volume fraction of whiskers are the same, whiskers with smaller radius have stronger inhibition effect on grain boundaries migration and lead to better grain refinement effect. When the radius and volume fraction of whiskers are the same, the whisker length has little effect on grain growth velocity.The computation model of effective elastic constants for inhomogeneous three-phase composite ceramic tool materials has been established. The computation program'EEC' of effective elastic constants for inhomogeneous ceramic tool materials has been developed by FORTRAN97. By applying homogeneous boundary load condition, the effective elastic constants of single-phase polycrystal, and the whisker and particle toughened ceramic materials have been predicted.A kind of nano-composite ceramic tool material Al2O3/Al2O3n/SiCn has been developed to verify the MC simulated results. The established MC models and the simulation results in the dissertation are convinced.