RU2642508C1 - METHOD FOR PRODUCING HIGH-COERCIVITY MAGNETS FROM ALLOYS ON BASIS OF Nd-Fe-B - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention can be used for production of high-energy permanent magnets based on rare-earth-alloys (rare earth metals), and alloys, in particular, based on neodymium, iron and boron (Nd-Fe-B alloy). The method for production of high-coercive magnets from Nd-Fe-B-based alloys includes crushing the base alloy, mixing the alloy and an additive for correction of alloy composition, pressing a mixture of powders in magnetic field, sintering the blank and cooling. The additive for correction of alloy composition is hydrides of rare-earth metals-Fe, and sintering of magnet is carried out in vacuum or at residual pressure for 1-2 h.

EFFECT: invention makes it possible to increase coercive force and residual induction of produced magnets.

2 cl, 2 dwg

Description

The invention relates to the field of permanent magnets and can be used in the production of high-energy permanent magnets based on rare-earth (REM) alloys and, in particular, on the basis of neodymium, iron and boron (Nd-Fe-B alloy).

Permanent magnets (PM) made of ternary alloys with a neodymium content of up to (33-34)%, obtained by out-of-furnace fluoride technology, have a relatively low coercive force and high values of residual magnetic induction.

To obtain high energy-intensive PM with high values of coercive force, the chemical composition of these alloys can be adjusted.

A permanent magnet and a method for its manufacture are known [RU 2458423, H01F 41/02, H01F 1/053, СВВ 35/04, publ. 08/10/2012], which discloses a method of manufacturing a permanent magnet with Dy or Tb, diffused into the crystalline grain-boundary phase of the sintered magnet. A sintered magnet based on iron-boron-rare-earth element is placed in a working chamber, which is heated to a certain temperature, evaporating evaporating material, which is placed in the same or another working chamber and consists of a hydride containing at least one of Dy and Tb. The vaporized vaporizing material adheres to the surface of the sintered magnet, and the metal atoms Dy and / or Tb in the mating vaporizing material diffuse into the crystalline grain-boundary phase of the sintered magnet.

The disadvantage of the proposed method for adjusting the composition of the alloy is that the adjustment occurs only in the surface layers of the magnet, in addition, as a result of the evaporation of Dy and / or Tb, the pairs of these metals will inevitably settle not only on the surface of the magnet, but also on the walls of the working chamber, which will result to cost overruns of expensive materials.

A known method of producing highly coercive magnets from alloys based on Nd-Fe-B [RU 1243947, H01F 1/053, H01F 41/02, publ. 02/27/2013]. The method is carried out by diffusion annealing of sintered magnets at a temperature of 600-1000 ° C, the surface of which is in contact with dispersed powders of diffusion source materials, based on dysprosium and / or terbium. As sources of diffusion, dispersed metal dysprosium (Dy) or terbium (Tb) powders, Dy and / or Tb hydride powders or alloy powders based on intermetallic compounds with a low melting point (500-1200 ° C) are used as diffusion sources. In this case, diffusion annealing is carried out for 0.5-20 hours at a temperature of 550-850 ° C, followed by additional annealing at a temperature of 550-600 ° C for 0.5-1.0 hours

The disadvantage of the proposed method for adjusting the composition of the alloy is that the adjustment occurs only in the surface layers of the magnet, in addition, the presence in the process of several long-term high-temperature redistribution increases the energy consumption for the production of magnets.

The closest effect to be achieved is the invention "Magnetic material for permanent magnets and a method for its manufacture" [RU 2136068, H01F 1/057, C22C 1/04, publ. August 27, 1999], adopted as a prototype. The invention describes a method for manufacturing a magnetic material, which includes crushing a base alloy and an additive alloy, mixing alloys, compressing a mixture of powders in a magnetic field, sintering a workpiece, and cooling.

The disadvantage of the proposed method is the difficulty in the manufacture of fine powder alloy additives, because the resulting metal powders are highly active, pyrophoric and should be stored and used exclusively in an inert atmosphere.

The problem to which the invention is directed, is to obtain permanent magnets with high magnetic properties by adjusting the composition of the magnetic alloy, with the ease of working with powder additives and relatively low specific energy consumption.

The problem is solved in that the method of producing highly coercive magnets from alloys based on Nd-Fe-B includes crushing the base alloy, mixing the alloy and additives to adjust the composition of the alloy, pressing the powder mixture in a magnetic field, sintering the workpiece and cooling, using additive (3-8)% wt. by weight of the alloy to adjust the composition of the alloy, which is the hydrides of the ligature of rare-earth metals-Fe in the form of (rare-earth metals _x + Fe) with particle sizes (0.5-1) mm, and the sintering of the magnet is carried out in vacuum or at a residual pressure of up to 10 Pa at temperatures (1100-1250) ° C for 1-2 hours

The drawings show the following graphs:

- FIG. 1. Demagnetization curves of magnets obtained by TFL with metal ligatures;

- FIG. 2. Demagnetization curves of magnets obtained by TFL by ligature hydrides.

Curve "0" refers to the base magnetic alloy 32Nd-Fe-1.1 V, and curves 1-4 to magnets with corrected chemical composition of additives: 75Nd-Fe, 42Dy-Fe, 40Tb-Fe and 70Tb-Fe, respectively.

The main stages of adjustment (solid-phase alloying) of the composition of magnets based on Nd-Fe-B were as follows:

1) crushing and grinding of an ingot of a magnetic alloy;

2) adding at the grinding stage the hydride of the ligature of REM-Fe in the form of (REMA _x + Fe) in an amount of (3-8)% wt. by mass of alloy;

3) pressing and sintering the mixture at a temperature of (1100-1250) ° C;

4) magnetization of sintered samples.

When the mixture is pressed and sintered at a temperature of (1100-1250) ° C, REMA _x is completely dehydrogenated, hydrogen is removed from the working volume, and the REM obtained by dehydrogenation complements the alloy composition and participates in the recombination of the Nd ₂ Fe ₁₄ B phase, resulting in the preparation of a permanent magnet the necessary composition.

The experiments showed that the addition of ligatures in metallic form at the stage of fine grinding of magnetic alloys mainly affects the coercive force of magnets. The value of the residual magnetic induction either decreases or remains at the same level. This is also confirmed by the demagnetization curves shown in FIG. 1. It is seen that there was an increase in coercive force by 1.5-3 times, but at the same time, the value of residual induction decreased. This happened due to the partial oxidation of the chemically active ligature, as a result of which it played a more role as interfacial ballast than a building material for the magnetic phase.

When solid-phase doping with hydride powders (Fig. 2), non-oxidized, easily ground hydride powders increase the coercive force and residual induction of the resulting magnets. The manufacturing process of magnets using solid-phase alloying (TFL) of Nd-Fe-B alloys with powders of REM-containing alloys obtained by mechanical and hydride grinding showed that:

- the use of mechanically ground powders for TFL leads to an increase in the coercive force of the magnets, while the residual magnetic induction either remains the same or decreases slightly. In some cases, especially with a high content of rare-earth metals in ligatures (more than 80%), particle hardening was visually observed in grinding products;

- TFL process with hydride powders is an effective way to increase the properties of magnets and adjust the chemical composition of Nd-Fe-B magnetic alloys.

In addition, the proposed method is distinguished by the simplicity of working with ligature hydride powders in comparison with metal powders. Ligature metal powders are highly active and pyrophoric substances, therefore they should be stored and used exclusively in an inert atmosphere. Hydride powders are free from these disadvantages and it is sufficient to store them in a dry airtight container. Weigh, pour, grind, mix and transport them in the open air.

When adjusting the composition of the alloy with ligature hydride powders, no additional heat energy is required.

Claims (2)

1. A method of producing highly coercive magnets from Nd-Fe-B-based alloys, including crushing a base alloy, mixing the alloy and additives to adjust the composition of the alloy, pressing the powder mixture in a magnetic field, sintering the workpiece and cooling, characterized in that it is an additive to correct the composition alloy are hydrides of the ligature of rare-earth metals-Fe in the form of (rare-earth metals _x + Fe) with particle sizes (0.5-1) mm in an amount of (3-8)% wt. by weight of the alloy. 2. The method according to p. 1, characterized in that the sintering of the magnet is carried out in vacuum or at a residual pressure of up to 10 Pa at a temperature of (1100-1250) ° C for 1-2 hours

Images