| 초록 |
WC grains grow during liquid phase sintering and the change of grain size strongly affects the mechanical properties of cemented carbides. Therefore control of microstructure is very important to produce highly qualified cutting tools. The grain growth process on cemented carbides can be characterized by continuous and discontinuous ones. Continuous grain growth is recognized as a uniform growth of the individual grains. Discontinuous grain growth is known as an undesired formation of isolated coarse WC grains which grow faster and larger than the surrounding grains. The grain growth in liquid phase sintered materials, which is generally understood as a solution/reprecipitation process called Ostwald ripening, has often been studied from a theoretical point of view In the present study, the Monte Carlo computer simulation technique is utilized to investigated continuous and discontinuous grain growth mechanisms in cemented carbides. Because grain growth simulation using the Monte Carlo method is considered to be useful for understanding the grain growth behavior in complicated systems. In addition to the simulations, experiments on microstructures of cemened carbides are preformed. Comparing the simulations to the experimental results, the grain growth mechanism is discussed with special focus on presence of WC/WC grain boundaries. The Ostwald ripening process (solution/re-precipitation) and the grain boundary migration process are assumed in the simulation as grain growth mechanism. The effects of liquid phase fraction, grain boundary energy and an implanted coarse grain are examined. The results of these simulation qualitatively agree with experimental ones and suggest that distribution of liquid phase and carbide particle/carbide grain boundary energy as well as contamination by coarse grain are important factors controlling discontinuous grain growth in cemented carbides. |
