[O3] Processing

2:50 PM - 3:05 PM JST(5:50 AM - 6:05 AM UTC)

[O3-6] A NOVEL APPROACH FOR SINTERING Nd₂Fe₁₄B-, SmCo₅- and Sm₂Co₁₇-BASED MAGNETS BY THE HDDR PROCESS

*Ihor I. Bulyk^1,2,4, RenHui Liu^1,2, HePing Zhu¹, SuJuan Wang¹, MuNan Yang^1,2,3, Ihor V. Borukh⁴, Oleksandr P. Kononiuk⁴ (1. Jiangxi University of Science and Technology (China), 2. National Rare Earth Functional Materials Innovation Center (China), 3. Ganjiang Innovation Academy, Chinese Academy of Science (China), 4. Karpenko Physico-Mechanical Institute of National Academy of Sciences of Ukraine (Ukraine))

Keywords:

Rare earth permanent magnets,Sintering,Hydrogenation,disproportionation,desorption,recombination,Fine microstructure

The latest approaches to the use of the hydrogenation, disproportionation, desorption, recombination (HDDR) process for the treatment of Nd₂Fe₁₄B-type materials, along with new data on the peculiarities of the HDDR method in SmCo₅ and Sm₂Co₁₇ ferromagnetic materials and application of this method to sinter them are presented. The results indicate that reviving interest in the HDDR technique promises new perspectives for technologies in the field of rare earth permanent magnet materials. The use of the HDDR treatment of Nd-Fe-B materials is well known and started shortly after the discovery of this type of ferromagnetic materials. We propose to use a pressure-composition-temperature diagram for the Nd-Fe-B alloy-hydrogen system to choose the HDDR treatment parameters [1]. Namely, according to the diagram, the parameter values of the HD stage should be shifted towards lower hydrogen pressure and lower temperatures in the range between the temperatures of the start and the end of the disproportionation reaction. The phase composition, microstructure and degree of texture of HDDR-treated sintered Nd-Fe-B magnets were investigated at hydrogen pressures of 10-50 kPa and the disproportionation temperatures of 715-785 °C. It has been shown for the first time that the HDDR technique is a promising way to sinter the Nd-Fe-B type magnets at low temperatures, namely below 850 °C, and to form their very fine microstructure [2]. The influence of the HDDR parameters during sintering on the density, microstructure, degree of texture and magnetic properties of the sintered magnets has been evaluated. The first results of using the modified HDDR approach together with hot pressing, hot deformation and grain boundary diffusion processes to produce permanent magnets are presented. The microstructure and magnetic properties of the magnets have been investigated. A relatively low pressure has been used for HDDR in SmCo ferromagnetic alloys. The HD reaction in the SmCo₅-H₂ system takes place at a hydrogen pressure of 0.2-0.5 MPa and a temperature of ~560 °C. Disproportionation is complete when the material has been held at the reaction temperature for 2-5 hours. During the DR stage the alloy consists of Sm₂Co₇, Sm₂Co₁₇ and SmCo₅ phases, with the highest SmCo₅ phase content observed after DR at 950 °C. The first results of sintering SmCo₅-type materials by the HDDR route at low temperatures have been presented. The microstructure of these materials is fine, with the grain sizes in the range of 40-140 nm. The porosity of the SmCo₅ based alloy is low, less than 1%. The high coercivity of ~50 kOe for the sintered SmCo₅-type magnet was achieved by HDDR post-sintering treatment [3].The peculiarities of the HDDR process in Sm₂(Co,M)₁₇ alloys, where M=Fe, Ti, V, Nb, have been studied. The influence of the hydrogen pressure during the disproportionation reaction in Sm₂Co₁₇-based alloy on the degree of the disproportionation has been determined. It was shown that disproportionation of the Sm₂Co₁₇ phase occurs at a pressure of 1.5 MPa. Alloying of the Sm₂Co₁₇ alloy with other metals influences the hydrogen pressure during the disproportionation reaction. The HDDR process has been successfully applied to sinter the Sm₂Co₁₇-based alloys at low temperatures and form their fine microstructure [4]. The grain sizes of the ferromagnetic phases after HDDR are in the range of 80-140 nm for the Sm₂Co₁₇ based alloy. The assumption that the material is textured when it contains remnants of the main ferromagnetic phase has been experimentally demonstrated for of Nd₂Fe₁₄B-, SmCo₅-, and Sm₂Co₁₇--+type ferromagnetic materials.

1. I.I. Bulyk, et al., Intermetallics 148 (2022) 107621. https://doi.org/10.1016/j.intermet.2022.107621.
2. I.I. Bulyk and I.V. Borukh, Powder Metall. Met. Ceram., 61 (2023), 657-669. https://doi.org/10.1007/s11106-023-00354-9.
3. I. Bulyk, et al., J. Alloys Compd. 866 (2021) 158272. https://doi.org/10.1016/j.jallcom.2020.158272.
4. I.I. Bulyk and O.P. Kononiuk, Powder Metall. Met. Ceram., 61 (2023) 548-559. https://doi.org/10.1007/s11106-023-00344-x.