Electronic properties, magnetic properties and phase stability of alloyed cementite (Fe,M)3C (M=Co,Ni) from density-functional theory calculations

First-principles calculations have been performed to investigate the magnetic properties and phase stability of alloyed cementite with Co or Ni. The calculations show Co and Ni reduce the stability of cementite and (Fe,M)3C (X = Co/Ni) form more difficultly than cementite. We predict that Ni and Co additions in high Co and Ni alloyed steels will promote the dissolution of the cementite. The magnetic moments (Ms) of Fe2CoC, Co2FeC, Fe2NiC and Ni2FeC are 4.86, 4.23, 3.95 and 2.41 μB/f.u, respectively. The Ms of Co in Fe2CoC (1.03 μB) and Co2FeC (1.09 μB) are different due to replacing different Fe atoms. The Ms of Ni in Fe2NiC and Ni2FeC are 0.14 μB and 0.15 μB, respectively. The Ms of alloyed cementite are mainly contributed by 3d electrons of metal atoms.

Graphical abstractElectron density differences maps of the plane with metal atoms and C atoms plane of the density values are plot from −0.15 electron/Å3 (blue) to +0.15 electron/Å3 (red). Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Ni and Co additions in high Co and Ni alloyed steels will promote the dissolution of the cementite. ► The magnetic moments of Fe2CoC, Co2FeC, Fe2NiC and Ni2FeC are 4.86, 4.23, 3.95 and 2.41 μB/f.u, respectively. ► The Ms of alloyed cementite are mainly contributed by 3d electrons of metal atoms.