Phase Compositions,Microstructures And Magnetic Properties Of PrNd-Lean Ce-Based Re₂Fe₁₄B Magnets

Due to the serious imbalance in the application of rare earth resources and the soaring price of Pr/Nd,the recent researches on cerium magnets have increased significantly.Besides of Ce,Y and La are also two kinds of main high abundant rare earths,but the research on Y,La added magnets is still rarely reported.In this paper,Ce-Fe-B,（Ce,Y）-Fe-B and（Ce,Y,La）-Fe-B magnets were prepared.The phase composition and microstructure characteristics of the magnets were analyzed and the effects of Y and La addition on the microstructure and magnetic properties of Ce-based magnets were studied.On this bases,the binary main phase（BMP）magnets were prepared from（Ce,Y,La）-Fe-B and（Ce,RE）-Fe-B（RE=Nd,Pr,Gd）alloys.The inhomogeneous distribution of rare earth elements in the BMP magnet was studied,and the mechanism of coercivity enhancement of the BMP magnets was discussed.Finally,the alloy ingots with the nominal composition of R₂Fe₁₄B（RE=Nd,Ce,Y,La）were prepared by arc melting method,and the solidification behaviors,phase composition characteristics,and phase transformation temperatures of RE-Fe-B alloy were discussed.This paper lays the foundation for the development of high abundant rare earth magnets.The main conclusions are as follows:（1）It was found that:the strip casting（SC）flakes of Ce-Fe-B,（Ce,Y）-Fe-B and（Ce,Y,La）-Fe-B alloys are mainly composed of RE₂Fe₁₄B,REFe₂,a small amount ofα-Fe,and other impurity phases.Moreover,the microstructures of the three SC flakes are not uniform.The magnetic properties of the three Ce-based magnets are rather low.For Ce-Fe-B magnets,there were many main-phase grains in direct contact without the isolation of rare earth-rich phases,the grains are abnormal growth,the coercivity of the magnet is very low;with Y addition,the phenomenon of main-phase grains in direct contact is obviously decreased,the coercivity is slightly increased;by co-addition of Y and La,the main phase grains is significantly refined,the microstructure is further improved,the coercivity of the magnet is obviously enhanced.The magnetic properties of（Ce,Y,La）-Fe-B sintered magnet have been obtained:B_r=8.31 k Gs,H_cj=0.924k Oe,（BH）_max=5.299 MGOe.（2）Pr Nd-lean Ce-based magnets（Pr Nd/ΣRE=25 at.%）prepared by the binary main phase（BMP）process have good comprehensive magnetic properties of H_cj=5.57k Oe,and（BH）_max=20.17 MGOe.Two kinds of grains with typical core-shell structure were found in the BMP magnets,in which the compositions of the’cores’are obviously different,and the compositions of the’shells’are similar.Therefore,the magneto-crystalline anisotropy field（H_A）of the shells of the two grains tends to be consistent,so the BMP sintered magnets exhibit the anti-magnetization behavior similar to that of single main-phase magnets.For lower H_A main-phase grains,the’shell’layer has higher H_A than the core,which increases the nucleation field（H_N）of anti-magnetized domain,and improves the coercivity of the BMP magnets.（3）The preliminary study shows that:the RE₂Fe₁₄B alloy ingots with RE=Nd,Ce,Y,La have obviously different microstructures,which suggests their different solidification characteristics,phase composition and microstructure characteristics.For Nd-Fe-B and Ce-Fe-B alloy ingots are mainly composed of 2:14:1 main phase,α-Fe phase and rare earth-rich phase,however,being different from Nd-Fe-B alloy,the rare earth-rich phase is Ce Fe₂ phase in Ce-Fe-B alloy.After long time homogenization treatment at 900°C,theα-Fe phase is nearly disappeared in Nd-Fe-B and Ce-Fe-B alloys.For Y-Fe-B alloy ingots are mainly composed of 2:14:1 phase,2:17 phase forming a halo structure around 2:14:1 phase,and very small amount of 1:2 phase;La-Fe-B alloy ingot has a distinguished phase structure,the matrix isα-Fe phase and Fe-rich phase,and a small amount of La₂Fe₁₄B phase in it,which proves indirectly that the formation of La₂Fe₁₄B phase is rather difficult.