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Vol.32, No.8, 952 ~ 958, 1994

Title

Structure and Magnetic Properties of Non - Equilibrium Iron - Nitrides Prepared by Solid - Gas Reaction during Ball Milling

이충효Chung Hyo Lee, 고곡야 유Tamotsu Koyano, 수곡우일랑Uichiro Mizutani

Abstract

Pure iron powders are nitrified at room temperature by ball milling in NH₃ gas atmosphere. Super-saturated bcc iron-nitrides are obtained for the N concentration below 14.9 at.%N and the high temperature ε-phase with the hcp structure for more than 19.4 at.%N. The atomic volume of Fe in the metastable bcc phases is found to be smaller than that in the bct iron-nitrides reported in the literature. Saturation magnetization at room temperature gradually decreases with the nitrogen content, which is in sharp contrast to the enhancement in magnetization due to nitrification reported for the N-martensite. We have shown that mechanical alloying in the NH₃atmosphere can nitrify pure iron powders even at room temperature and gives rise to the super-saturated bcc iron-nitrides up to 14.9 at.% N. The high temperature ε-phase with the hcp structure is obtained for the iron-nitrides containing more than 19.4 at.%N. In the composition range between 14.9 at.%N and 19.4 at.%N, a mixture of the bcc and hcp phases is produced. The stomic volume of Fe in the bcc phase is found to be smaller than that in the N-martensite. We also reveal that the magnetization at room temperature gradually decreases with the N concentration. Here a lack of the tetragonal distortion has been proposed to be the tetragonal distortion has been proposed to be the likely cause for the low value of saturation magnetization compared to bct iron-nitrides.

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