イオン窒化過程におけるN₂⁺電界加速のモンテカルロシミュレーション

抄録

A Monte Carlo computer simulation was performed to investigate the fundamental roles of N₂⁺ acceleration in an ion nitriding process. The calculation results showed incident energy of N₂⁺ to the cathode was mainly affected by the changing gas temperature when the electric field was assumed to be unchanged. Therefore incident energy increases with increasing gas temperature in a cathode fall region. In addition, two major roles of N₂⁺ acceleration were proposed; (1) direct gas heating in the region near the cathode and (2) sputtering for the surface of the cathode. In order to reveal the effects of the increasing gas temperature or sputtering rate on well-nitriding, the samples of SCM420 were treated using dc plasma reactor with a tungsten hot filament. In this equipment, the reactant gas is heated directly by the hot filament settled around the cathode. Therefore incident energy of cations can be controlled with changing filament temperature. The nitriding speed of the sample increased with increasing filament temperatures in the range of ≤1610 K, suggesting that the amount of radicals required for nitriding becomes larger with increasing gas temperature. However nitriding was inhibited over 1610 K because of the increase in sputtering rate by cations incident on the sample. These results suggest that the optimum acceleration of N₂⁺ affects for well-nitriding through gas and sample heating. However, exceeded acceleration gives the sample severe sputtering, resulting in the inhibition of well-nitriding.