Determination of the site preference on the structure, magnetism and mechanical anisotropy properties of Mo-containing alloy carbide M₆C (M = Fe, Mo)

Abstract

First-principles calculations are used to study the structure, magnetism and mechanical anisotropy properties of M6C (M=Fe, Mo) carbides. The stability of alloy carbide M6C can be improved when Mo atoms occupy the 48f Wyckoff position. Fe3Mo3C 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 Fe4Mo2C and Fe3Mo3C (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.

Review of Microstructure–Mechanical Property Relationships in Cast and Wrought Ni‐Based Superalloys with Boron, Carbon, and Zirconium Microalloying Additions

“…However, Nb, Ti, Ta, and Zr may also be observed. M 6 C also have been described as η carbides and can adopt stoichiometries, such as A 2 B 4 C and A 4 B 2 C. [128,131,133,134] Thermodynamic models may assume four sublattices for improved description of substitutional and interstitial species. [135] M 6 C is usually not considered detrimental to processability and can provide beneficial GB pinning.…”

“…M 6 C and M 23 C 6 are secondary carbides formed primarily via solid‐state phase transformations during thermo‐mechanical processing. [ 128–130 ] Mo‐rich M 6 C carbides have a E9 3 ordered A 3 B 3 C crystal structure and tend to form blocky, discrete particles between 815 and 1100 °C, [ 6,127,128 ] as shown in Figure 5c,d. They have been observed to form in Ni‐based superalloys with a combined (Mo + W) content of over 6 wt%.…”