Simulation Study On Microstructure Evolution Of Ceramic Tool Materials During Fabrication

The advanced ceramic tools have been one of the most important cutting tools applied in high efficiency and precision machining because of its high hardness, good wear resistance and elevated-temperature anti-oxidation. However, the fracture toughness of ceramic tools is low at the present time and the mechanical properties of ceramic tools are governed by its microstructure. In order to provide the theory guide for the improvement in the fracture toughness, it is very significant to simulate and optimize the microstructure of ceramic tool materials.The microstructure evolution for the ceramic tool materials during fabrication has been simulated with the Monte Carlo Potts model. The novel H-F Monte Carlo simulation algorithm is proposed based on the systemic research of the present Monte Carlo Potts simulation algorithm and verified by experiments.In the H-F Monte Carlo simulation algorithm, a grain lattice is randomly chosen in simulation space firstly, and then the grain lattice which lies in the grain boundary is used to attempt another reorientation. So, the H-F Monte Carlo simulation algorithm has more efficiency than the present Monte Carlo simulation algorithm. The H-F MCSPI and R-Z MCSP software have developed with Visual C++ compiler and C++ program language on the base of H-F Monte Carlo algorithm and R-Z Monte Carlo algorithm respectively. The microstructure evolution has been simulated with the H-F MCSPI and R-Z MCSP. The simulation efficiency of H-F Monte Carlo algorithm is remarkably higher than that of R-Z Monte Carlo algorithm. The grain coarsening effect is eliminated when the grain orientation value Q is equal to 90, 150 and 200 respectively. The satisfying simulation results can be gained when the grain orientation Q and the lattice size space are 200 and 500 X 500 respectively.The Monte Carlo Potts model for simulating the microstructure evolution of the two-phase ceramic tool materials has been established. The model contains all boundary energy in the material system and the diffusion between the matrix and the second-phase material. The simulation space with the initial grain radius is adopted creatively at the beginning of the simulation for the microstructure evolution during the fabrication of the ceramic tool materials. The microstructure evolution of two-phase ceramic tool materials is simulated under the regular and irregular cell condition with the developed H-F MCSPII simulation software. At the same time, the proportion of grain boundary energy, the initial shape of powders and contents are considered. It is shown that the matrix which has the same grain boundary energy diffuses easily each other, and the grain grows fast. The second particles can inhibit the matrix grain from growing, and the inhibitation function increases with an increment in the content of second particles. However, the inhibitation by second phase particles decreases with an increment in the boundary energy between the matrix and the second phase. The simulated microstruture that adopts the irregular cell is more similar with that of the real ceramic tool materials than the simulated microstruture that adopts the regular cell.The Monte Carlo Potts model, which can simulate the microstructure evolution for the ceramic tool materials containing pores, liquid phase and additives during fabrication, has been established. The microstructure evolution for the ceramic tool materials containing pores, liquid phase and additives during fabrication is simulated on the base of the developed H-F MCSPI and H-F MCSPII simulation software. It is shown that both the change trend of the densification with the simulation time and the densification of the single- and two-phase ceramic tool materials during fabrication is similar. The mean grain radius of the two-phase ceramic tool materials is always lower than that of the single-phase ceramic tool materials. The liquid phase benefits the densification during fabrication. The additives pin the grain growth strongly and impede the grain growth significantly. At the same simulation time, the simulated mean grain radius without the pores is larger than that with the pores. The mean grain radius increases with an increment in the simulation time.The relationship between simulation time and real duration time is established. The relationship between fabrication temperature and the microstructure evolution and relationship between fabrication pressure and the microstructure evolution are also established and incorporated into the simulation program. The microstructure evolution of ceramic tool materials is simulated with the fabrication parameters during the fabrication. The simulated mean grain radius increases with an increment in the simulation time. The simulated mean grain radius also increases with an increment in the fabrication temperature using the temperature factor. And the simulated mean grain radius increases with an increment in the fabrication pressure, however, the effect of the fabrication pressure on the grain growth is lower than that of the fabrication temperature. The simulation model is desirable because the simulation results with the fabrication parameters mentioned above are consistent with the practical experiment results.The microstructure evolution of single- and two-phase Al₂O₃ matrix ceramic tool materials is simulated under the simulation space containing pores, liquid phase and additives. The simulation results are verified. It is shown that the simulated mean grain diameter is slightly lower than the measured mean grain diameter, this is because that the MgO is treated as inert particles to pin the grain growth only, the rearrangement of particles caused by the liquid phase is omitted, the grain boundary energy is assumed to lie among the initial powders at the beginning of simulation, the grain boundary diffusion is only considered and other kinds of diffusions are neglected, etc. Because the error ratios of the simulated mean grain diameter and the measured mean grain diameter of ceramic tool materials are only from 12.1% to 18.2%, the simulation precision is high enough to be accepted. The simulation of the ceramic tool materials lays a foundation for designing the new ceramic tool materials and optimizing the fabrication parameters and mechanical properties of ceramic tool materials.