MAによる(Cr0.7Fe0.3)-N系のアモルファス化とその原子構造観察

概要

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Cr and Fe elemental powders at 7:3 atomic propotion were milled in a vibrational ball mill under N2 gas atmosphere. The concentration of N atoms in the Cr0.7Fe0.3-N powders increased with increasing MA time and approached to about 15at%N after 320 hours of milling. The amorphization was observed by X-ray diffraction and DSC measurements. RDF(r) shows that the 2nd nearest neighbor atoms in BCC crystal preferentially moved out of their positions during the amorphization process and the 1st nearest neighbor distance between metal atoms increases with increasing the milling time. The nearest coordination number around a metal atom within about 3.3 A decreases from 14 to 12.5 atoms while the amorphization proceeds. These results definitely tell us that the octahedral unit in a BCC structure is destroyed and is transformed into the tetrahedral unit during the amorphization process. An increase in the metal-metal distance of the 1st nearest neighbor with increasing nitrogen content can be interpreted by the penetration of a nitrogen atom into a polyhedron formed by metal atoms.
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