Determination of the site preference on the structure, magnetism and mechanical anisotropy properties of Mo-containing alloy carbide M 6 C (M = Fe, Mo).

First-principles calculations are used to study the structure, magnetism and mechanical anisotropy properties of M ₆ C (M = Fe, Mo) carbides. The stability of alloy carbide M ₆ C can be improved when Mo atoms occupy the 48f Wyckoff position. Fe ₃ Mo ₃ C with Mo atoms occupying 48f position and Fe atoms occupying 16d and 32e positions has the best structural stability. The magnetic moment is triggered when the Fe content is approximately 0.5, suggesting that there exists a critical value between the paramagnetic nature and ferromagnetism. Carbides with Fe content above 0.5 have stronger magnetism. Higher Fe content corresponds to the stronger chemical bonding of carbides, resulting in improved elastic properties when Mo atoms are held in 48f position. The special carbides Fe ₄ Mo ₂ C and Fe ₃ Mo ₃ C (Fe at 48f site, Mo at 16d and 32e sites) correspond to the excellent mechanical properties. These results are helpful in providing a theoretical foundation of the possible direction for the advances of the excellent physical properties in Mo-containing steel.
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