The Influence of Dehydrogenation Speed on the Microstructure and Magnetic Properties of Nd-Fe-B Magnets Prepared by HDDR Process

Abstract

The influence regarding the dehydrogenation speed, at the desorption-recombination state during the hydrogenation-disproportionation-desorption-recombination (HDDR) process, on the microstructure and magnetic properties of Nd-Fe-B magnetic powders has been studied. Strip cast Nd-Fe-B-based alloys were subjected to the HDDR process after the homogenization heat treatment. During the desorption-recombination stage, both the pumping speed and time of hydrogen were systematically changed in order to control the speed of the desorption-recombination reaction. The magnetic properties of HDDR powders were improved as the pumping speed of hydrogen at the desorption-recombination stage was decreased. The lower pumping speed resulted in a smaller grain size and higher DoA. The coercivity and the remanence of the 200-300 µm sized HDDR powder increased from 12.7 to 14.6 kOe and from 8.9 to 10.0 kG, respectively. In addition, the remanence was further increased to 11.8 kG by milling the powders down to about 25-90 µm, resulting in (BH) max of 28.8 MGOe.

Design of High-Remanence Nd-Fe-B Hot-Pressed Magnets by Manipulating Coercivity of Hydrogenation-Disproportionation-Desorption-Recombination Treated Anisotropic Precursors

“…To prepare anisotropic HDDR powders with different H cj values, alloys with compositions of Nd x Fe 87.2-x Nb 6.6 Ga 0.6 B 5.6 (at.%) (x = 11.8, 12.0, 12.2, and 12.5) were employed as the starting materials. The anisotropic HDDR powders were produced via the HDDR process under a condition optimized in our previous study [30], as follows: First, the powders were heated up to 840 • C under an Ar gas atmosphere with a pressure of 1.1 atm. When the temperature reached up to 840 • C, H 2 gas flowed at a pressure of 0.3 atm for 90 min to induce an HD (hydrogenation-disproportionation) reaction.…”

Effect Of The Desorption-Recombination Temperature On The Microstructure And Magnetic Properties Of HDDR Processed Nd-Fe-B Powders

“…After heat treatment, they were transferred directly to the glove box and then crushed into powders of 200-300 µm under Ar atmosphere with less than 1 ppm oxygen and water contents. After being transferred to the furnace again, they were subjected to Modified Solid HDDR (MS-HDDR) treat-ment [9,10]. The powders were heat treated at 200 • C for 30 min in H 2 atmosphere.…”

Limitations in the Grain Boundary Processing of the Recycled HDDR Nd-Fe-B System

“…The hydrogenation-disproportionation-desorption-recombination (HDDR) is a well-established and greener route for developing anisotropic ultrafine grains (~400 nm) with preferential easy-axis orientation [ 3 ]. The overall surge in production volume and application demand has necessitated the utilization of recycled REPMs into the industrial feedstocks [ 4 , 5 ]. The effectiveness of hydrogen gas towards decrepitating (HD) and disproportionation (HDDR) of the end-of-life rare-earth (RE) scrap has convincing been proven in previous studies [ 6 , 7 , 8 , 9 , 10 , 11 , 12 ].…”