Ultra-fine-grain NdFeB permanent magnetic material and preparation method thereof

Abstract

The invention discloses an ultrafine-grain NdFeB permanent magnetic material and a preparation method thereof. The permanent magnetic material comprises raw materials including, by weight, 25-35% of Nd, 55-70% of Fe, 0.5-1.8% of B and an auxiliary material, the auxiliary material is nanoscale high-melting-point metal powder, and the nanoscale high-melting-point metal powder accounts for 0.5-2% of total weight of Nd, Fe and B. The preparation method includes: tableting; breaking; fine grinding; adding the auxiliary material; wet ball milling; scattering; pressing for forming; sintering. The magnetic material and the preparation method have the advantages that the advantage that nanoscale high-melting-point metal is difficult to melt in the process of sintering is utilized to realize pinning effect at a grain boundary to prevent NdFeB grain growth so as to prepare the NdFeB permanent magnetic material having ultrafine-grain tissue, and the permanent magnetic material is enabled to have extremely high coercivity without adding rare earth elements like Dy and Tb.

Description

technical field [0001] The invention belongs to the technical field of rare earth permanent magnet materials, and in particular relates to an ultrafine crystal NdFeB permanent magnet material and a preparation method thereof. Background technique [0002] NdFeB series rare earth permanent magnet material is a kind of permanent magnet material with the best magnetic properties so far. It is widely used in machinery, information, transportation, medical treatment and other fields. It is an important material basis indispensable for modern science and technology and the development of the world economy. Extremely important application value and broad application prospects. According to different preparation techniques, NdFeB permanent magnet materials can be mainly divided into three types: sintering, bonding and hot pressing. Among them, sintered NdFeB permanent magnet materials not only have extremely high energy density, but also are easy to realize industrial production, so...

AI Technical Summary

Problems solved by technology

Among them, in order to prevent the oxidation of NdFeB alloy, in the "jet mill" of the above step (2), it is impossible to prepare NdFeB alloy powder with a small particle size (generally above 1 μm); moreover, in the sintering process (4), from NdFeB The Nd2Fe14B grains formed by the alloy powder will grow further

Therefore, the sintered NdFeB permanent magnet material prepared by the traditional method generally has a grain size of about 5 μm, and cannot obtain extremely high coercive force.

[0005] In order to improve the coercive force of NdFeB materials, a series of improvement methods have been proposed, such as: (1) By element substitution, heavy rare earth elements such as Dy and Tb are added to the master alloy to adjust the grain or grain boundary layer Composition and magnetocrystalline anisotropy field Ha, intrinsically improve the coercive force of the material; however, this method requires the use of expensive Dy, Tb heavy rare earth elements, which greatly increases the material cost, and because Dy / There is a reverse magnetization coupling effect between Tb and Fe atoms, which seriously reduces the remanence and magnetic energy product of permanent magnet materials; (2) By optimizing the process or adding other elements, adjusting the composition and distribution of grain boundary phases and reducing defects to achieve improved The purpose of the coercive force of the material; however, this method needs to add a certain amount of non-magnetic elements at the grain boundary, resulting in an increase in the total amount of non-magnetic phases in the permanent magnetic material, reducing the remanence and energy product of the material

In addition, the Sagawa research group in Japan also proposed a pressureless sintering technology. They prepared ultra-fine-grained NdFeB permanent magnet materials with a main phase grain size of less than 1 μm through a new type of helium jet milling and pressureless sintering technology. Since the ultra-fine NdFeB alloy powder is easily oxidized in the jet milling process, the oxygen content in the final material is greatly increased, and it is still impossible to prepare NdFeB permanent magnet materials with ideal magnetic properties.

Moreover, since this method requires a very high degree of vacuum in the preparation process, it is currently relatively difficult to realize industrial production.

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