DFT investigation of carbon-expanded α phase with different alloying element

• Published in: Vacuum 2022-08, Vol.202, p.111199, Article 111199
• Main Authors: Song, T.Y., Liu, R.L., Li, L.Z., Bian, C.X., Yan, M.F.
• Format: Article
• Language: English
• Subjects: Carbon-expanded α phase; Electronic structure; First-principles calculation; Low-temperature carburizing; Mechanical property
• ISSN: 0042-207X; 1879-2715
• DOI: 10.1016/j.vacuum.2022.111199

The structures of carbon-expanded α phase (αC) phase were modeled with nominal molecular formula of Fe13-xCr3NixCy (x = 0, 1, y = 0,1,2,3,4) based on body-centered cubic α-Fe and calculated by first-principles calculation using density functional theory (DFT). The results show that Fe13Cr3Cy (y = 0,1,2,3,4) structures with less than 11.11 at% carbon (y = 2) can be easily formed and exist stable. The Young's moduli of stable Fe13Cr3, Fe13Cr3C, and Fe13Cr3C2 are 227.08 GPa, 209.71 GPa and 189.19 GPa, respectively. The theoretical hardness of stable Fe13Cr3Cy (y = 1, 2) are obviously improved and can be up to 8.26 GPa. As for Fe12Cr3NiCy (y = 0,1,2), Young’ s moduli of Fe12Cr3Ni, Fe12Cr3NiC, and Fe12Cr3NiC2 are 155.82 GPa, 258.24 GPa and 207.44 GPa, respectively. The hardness of Fe12Cr3NiCy (y = 1,2) can be as high as 17.88 GPa. Ni element can stabilize the structures of Fe13Cr3Cy (y = 1,2) and improve their theoretical hardnesses. The toughness of Fe13Cr3Cy (y = 1,2) structures are shown in ductility based on Pugh's ratio criterion, while the Fe12Cr3NiCy (y = 1,2) structures are shown in brittleness. Electronic structure calculation shown that there are mixture bonding of metal bonding, covalent bonding, and ionic bonding in Fe13-xCr3NixCy (x = 0,1, y = 1,2) structures, which should account for the high hardness of the structure for αC phase. •Optimization position of Cr atom in α-Fe with BCC structure was obtained.•Hardness of stable Fe13-xCr3NixCy (x = 0, 1, y = 1,2) can be as high as 17.88 GPa.•Effects of Ni element on mechanical properties of αC phase were given.•New covalent bonding and ionic bonding account for high hardness of the structure for αC phase.