First-Principles Calculations of the Effect of M (Mn, Ti, Mo) Doping on the Stability, Mechanical Properties, and Electronic Structure of Fe3C

To design and regulate the composition and mechanical properties of Fe3C, the main reinforcing phase in steel, and subsequently control the steel’s mechanical properties, this paper employs first-principles calculations combined with orthogonal test analysis. It systematically studies the effects of doping with different elements M (Mn, Ti, Mo) on the stability, mechanical properties, electronic structure, and magnetic properties of cementite (Fe3C). The results indicate that M doping not only facilitates the formation of alloyed cementite but also enhances its mechanical stability. Co-doping with Mn and Mo improves the toughness of the alloyed cementite, whereas co-doping with Mn and Ti increases its brittleness. The alloyed cementite exhibits a mixture of metallic, covalent, and ionic characteristics. As the concentration of Mn and Mo co-doping increases, the overlap and hybridization between Fe 3d, Mn 3d, Mo 4d, and C 2p states are enhanced, thereby improving the mechanical stability of the alloyed cementite. Additionally, M doping reduces the magnetic moment of Fe3C. The magnetic behaviors of Ti and Mo in the alloyed cementite Fe3 – x – y – zMnxTiyMozC differ from those of Mn. Specifically, the magnetic moments of Mn at the 8d position are positive compared to those at the 4c position, while the magnetic moments of Ti at the 8d position are negative relative to those of Mo.