Novel hydrogen decrepitation behaviors of (La, Ce)-Fe-B strips

Jiaying Jin,Tianyu Ma,Yongsheng Liu,Yujing Zhang,Guohua Bai,Mi Yan,Baixing Peng

doi:10.1063/1.5006432

Abstract

La and Ce substitution for Nd in the 2:14:1-type sintered magnet is of commercial interest to reduce the material cost and to balance the utilization of rare earth (RE) sources. As hydrogen decrepitation (HD) is widely utilized to prepare the magnetic powders during magnets fabrication, incorporating La and Ce into the Nd-Fe-B permanent magnets, however, may exert complex influences on the decrepitation behavior. In the present work, through a comparative study of the HD behaviors between the (La, Ce)-Fe-B strips and the conventional Nd-Fe-B ones, we find that similar to the Nd-Fe-B system, increasing hydrogen pressures from 2.5 to 5.5 MPa do not break the 2:14:1 tetragonal structure of (La, Ce)-Fe-B strips. The enhanced hydrogen absorption behaviors are observed with increasing pressure, which are still inferior to that of the Nd-Fe-B strips. This should be ascribed to the higher oxygen affinity of La and Ce than that of Nd, leading to the decreased amount of active RE-rich phase and limited hydrogen diffusion channel. As a result, the hydrogen absorption of 2:14:1 matrix phase is significantly suppressed, dramatically weakening the exothermic effect. This finding suggests that La and Ce with stable 2:14:1 tetragonal structure upon HD process are promising alternatives for Nd, despite that more precise oxygen control is necessary for the microstructure modification and magnetic performance enhancement of (La, Ce)-Fe-B sintered magnets.

Highlights

Since its discovery in 1980s, Nd2Fe14B has been the strongest permanent magnets, which can provide a constant magnetic field once magnetized.[1,2,3] Despite the close-to-ideal magnetic performance, Nd-Fe-B magnet is currently in a dilemma due to the increasing demand and tightening supply of closely relied rare earth (RE) Nd/Pr/Dy/Tb.[4]
The following research on the hydrogen decrepitation (HD) behavior of (La, Ce)-Fe-B strip is necessary for further commercial application
XRD characterization reveals that increasing PH2 are not deteriorating the 2:14:1 tetragonal structure of (La, Ce)-Fe-B system even hydrogenated upon a high pressure of 5.5 MPa, similar to Nd-Fe-B decrepitated at 2.5 MPa

Summary

INTRODUCTION

Since its discovery in 1980s, Nd2Fe14B has been the strongest permanent magnets, which can provide a constant magnetic field once magnetized.[1,2,3] Despite the close-to-ideal magnetic performance, Nd-Fe-B magnet is currently in a dilemma due to the increasing demand and tightening supply of closely relied rare earth (RE) Nd/Pr/Dy/Tb.[4]. % Ce substitution.[12] the low-cost (Nd, La, Ce)-Fe-B sintered magnet is appealing for mass production. Re-crushing (e.g. jet milling) than the conventional powders.[16] The HD process has been demonstrated to exert a profound effect on the particle size and shape, and microstructure of the final magnets.[16,17,18,19] La and Ce substitution in both the RE2Fe14B matrix and RE-rich intergranular phases may result in distinct HD behaviors compared to the conventional Nd-Fe-B strips, influencing the microstructure and magnetic properties to a certain extent. It is necessary to study the HD behaviors of (La, Ce)-Fe-B strips to further modify the magnetic properties and to promote La/Ce for mass production

EXPERIMENT

RESULTS AND DISCUSSION

CONCLUSION