Thermodynamic Calculation And Experimental Study Of RE-B Binary Systems And Dy-Tb-Fe And Dy-Fe-B Ternary Systems

Rare earth Nd-Fe-B permanent magnet materials have been widely used in the industrial field due to their excellent magnetic properties.In order to meet the requirements of the development of science and technology for the performance,cost and output of rare earth permanent magnet materials,the research and development of low-cost and high-performance rare earth Nd-Fe-B permanent magnet materials has become a research hotspot.In the multi-component rare earth RE-Fe-B alloy system,the phase formation microstructure evolution laws between the rare earth metal and Fe,B and other elements are the basic key information for the research and design of new rare earth RE-Fe-B permanent magnets.Therefore,phase diagrams and thermodyanamic properties of RE-B(RE= Sm,Gd,Tb,Ho,Er,Tm,Y)and solidification microstructure of Dy-Tb-Fe and Dy-Fe-B ternary systems were studied in this paper.The main research contnts are as follow:(1)According to the literature information,the phase diagram and thermodynamic evaluation of the RE-B(RE=Y,Sm,Gd,Tb,Ho,Er,Tm)binary systems were carried out finally.Based on the phase diagram,the thermodynamic experimental data and the thermodynamic model,the CALPHAD method was employed to optimize seven RE-B binary phase diagrams,and obtained the thermodynamic parameters describing the Gibbs free energy of each phase in the RE-B systems.Combining the phase diagram and thermodynamic optimized evaluations of the RE-B(RE=La,Ce,Pr,Nd,Dy and Lu)binary systems reported in the literature,the analysis and summary of the law of the phase equilibrium and thermodynamic properties of the RE-B binary systems were obtained.It has shown that with the increase of the atomic number in the RE-B binary phase diagrams,more and more compound phases were formed.the enthalpy of mixing of liquid RE-B alloy reaches its minimum value around 60-70 at.% B,and with the increase of atomic number,the enthalpies of mixing of liquid RE-B alloy and the enthalpies of formation of compounds increase negatively.(2)Eight alloy samples of the Dy-Tb-Fe system(Dy:Tb = 1:1)were prepared by non-consumable tungsten electrode melting furnace.The phase composition,phase relationship and phase transition temperature of the alloy samples were determined experimentally.By CALPHAD method,the phase equilibrium of the Dy-Tb-Fe ternary system was optimized and the Scheil model was used to calculate and simulate the solidification path of the key alloys.The calculated vertical section(Dy:Tb = 1:1)is basically consistent with the experimental data,and the calculated solidification process is consistent with the experimental results.(3)Scanning electron microscopy(SEM),X-ray powder diffractometer(XRD)and Differential scanning calorimeter(DSC)were used to measure phase composition and phase transition of Dy-Fe-B alloys,and vertical sections with 70 at.% Fe and 85 at.% Fe were obtained.On this basis,using the CALPHAD method,the phase equilibria of the Dy-Fe-B ternary system were calculated.The calculated vertical section results are basically consistent with the experimental results.