Thermodynamic analysis of element-doped SmFe₁₂ rare earth alloy ingots

By adopting an appropriate alloy preparation method and element doping to regulate the composition and microstructure of alloy ingots, metal materials can be modified, which is an important means to address the problems of Sm element volatilization, poor preparation stability, and difficult microstructure control in SmFe₁₂-based rare earth alloys. Based on experimental phenomena, it was determined that induction melting method was more suitable for the preparation of SmFe₁₂-based rare earth alloy ingots than arc melting method. Zr, Co, Cu and Ti were doped into SmFe₁₂ alloy ingots, and the doped ingots were subjected to homogenization heat treatment at 1 100 ℃ for 36 h. The phase composition and microstructure were characterized and analyzed using XRD and SEM. The mechanism of the effect of element doping on the alloy phase composition was studied. The effect of element doping was analyzed from the perspective of thermodynamic parameters such as mixing enthalpy, mixing entropy, Gibbs free energy and atomic size difference. Combined with the experimental results and thermodynamic analysis, the problems of poor stability and difficult preparation of SmFe₁₂ alloy ingots have been addressed by element doping. Under the action of interatomic forces, Sm_0.8 Zr_0.2 Fe_8.5 Co₂ Cu_0.5 Ti alloy is composed of SmFe₁₁ Ti phase, SmCu₅ phase and α-Fe phase. Zr and Ti atoms exist in the form of solid solution in the SmFe₁₁ Ti phase, and the solid solubility of Zr and Ti is higher in the SmFe₁₁ Ti phase around the α-Fe phase. Under the attractive force of Cu atoms on Sm atoms and the repulsive force of Cu atoms on Fe atoms and Co atoms, Cu atoms are precipitated to form SmCu₅ phase, which promotes the decomposition of SmFe₁₁ Ti phase and leads to the decrease in SmFe₁₁ Ti phase content and the increase in α-Fe phase content. The results show that, the doping of Zr, Co, Cu and Ti elements improves the stability of the SmFe₁₂-based alloy's main phase while precipitating the SmCu₅ phase, which is expected to further optimize the magnetic properties of the SmFe₁₂-based alloys. High-quality raw materials are provided for future powder preparation, and control of the grain size and distribution of SmCu₅ phase becomes a new research direction.