JPH0517824A - Production of rare earth metal-transition metal type magnetostrictive material - Google Patents

Abstract

PURPOSE:To provide a heat treatment method for improving the magnetostrictive characteristics of a rare earth metal-transition metal type magnetostrictive material. CONSTITUTION:A rare earth metal-transition metal type magnetostrictive material consisting of an RTx (where R means Y and one or more rare earth elements, T means one element among Fe, Co, and Ni, and the symbol (x) stands for 1.5-2.0) alloy prepared by a unidirectional solidification process is subjected to homogenizing treatment, to heating, in a state where compressive force is applied in a solidification direction, up to a temp. not lower than the Curie point of the material, and then to cooling in a state where compressive force is applied. By this method, the material in which the necessity of the previous application of prestress to the magnetostrictive material at the time of using the magnetostrictive material and also the necessity of a large-sized magnetic field generator are obviated and which produces large magnetostriction can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare earth metal-transition metal based magnetostrictive material, and more particularly to a heat treatment method for improving magnetostrictive properties.

[0002]

2. Description of the Related Art Normally, rare earth / iron-based magnetostrictive materials are called giant magnetostrictive materials, and are expected to be applied to ultrasonic waves, sound wave related equipment, vibrator fine positioning devices, precision valves, sensors, etc. , Has been attracting attention recently.

As the magnetostrictive material, RT among the rare earth metal (R) -3d transition metal (T) type metal compounds is generally used.
_Two Laves phases are known. Specifically, R is Tb _0.3 Dy _0.7 , T is Fe, and Tb _0.3 Dy _0.7.
Fe ₂ (Fe ₂ is practically Fe _{1. 8-1.95)} (USP.
4,308,474) is known as a representative example. The magnetostriction of these intermetallic compounds RT ₂ has anisotropy and exhibits an extremely large magnetostriction of 2000 ppm or more in the <111> crystal direction, and it has been put to practical use by utilizing this large <111> magnetostriction.

In order to obtain an anisotropic material having a large magnetostriction, it is necessary to align the crystals in <111>. For this purpose, the Bridgman method and the zone melting method (USP. , 402), unidirectional solidification method (USP. 4,770, 704), and powder method (U
SP. 4,152,178) have been proposed. However, the crystal growth direction during solidification of this intermetallic compound is <1
12>, the crystal growth material of <111> has not been obtained at this point in the Bridgman method, the zone melting method, and the unidirectional solidification method, and the crystal material of <112> is used.

The material having the <112> crystal direction in the major axis direction has a twin structure having <112> twin planes,
As shown in FIG. 1, the <111> crystal direction includes the number 1 and the number 2 directions inclined by 19.5 ° from the major axis direction, and the number 3 and the number <111> oriented in the direction perpendicular to the major axis direction. .

[0006]

[Equation 1]

[0007]

[Equation 2]

[0008]

[Equation 3]

Generally, when using a giant magnetostrictive material, a compressive force (hereinafter referred to as prestress) is applied to the material in advance.
This improves the magnetostriction of the material at relatively low magnetic fields (0-80 KA / m). The principle that the magnetostriction improves when prestress is applied to the magnetostrictive material can be explained as follows.

The spin is oriented in the <111> direction (in FIG. 1, the spin is oriented in the number 4, the number 5, the number 6, the <111>, etc.). The magnetostriction is caused by the fact that when a magnetic field is applied in the longitudinal direction of the material, the crystal is distorted when the spin changes its direction due to the applied magnetic field. There are two ways to change the spin direction. It is a method of moving the domain wall and a method of rotating the spin itself (in the explanatory diagram, it is referred to as magnetization rotation).

[0011]

[Equation 4]

[0012]

[Equation 5]

[0013]

[Equation 6]

For example, when a magnetic field is applied in the longitudinal direction of FIG. 1, spins oriented in a direction perpendicular to the longitudinal direction (<111> and equation 7) are applied in a low applied magnetic field as shown in FIG. Number 8 tilted 19.5 ° in the longitudinal direction by
Then, the direction is changed to Expression 9 and magnetostriction occurs. This is caused by the domain wall movement, and the direction is changed to the easy axis of magnetization of Mathematical 10 to Mathematical 11 (or <111> to Mathematical 12), so the orientation is changed with relatively low magnetostatic energy (low applied magnetic field). be able to.

[0015]

[Equation 7]

[0016]

[Equation 8]

[0017]

[Equation 9]

[0018]

[Equation 10]

[0019]

[Equation 11]

[0020]

[Equation 12]

When a still larger magnetic field is applied, as shown in FIG. 3, the numbers 13 and 1 tilted by 19.5 ° in the longitudinal direction.
4 spins are applied magnetic field directions (Equation 15 and Equation 1)
Rotate to 6) and magnetostriction occurs. This is from number 17 to number 1
Since the direction is changed to the direction of the easy axis of magnetization of 8 (or 19 to 20), a considerably large magnetostatic energy is required.

[0022]

[Equation 13]

[0023]

[Equation 14]

[0024]

[Equation 15]

[0025]

[Equation 16]

[0026]

[Equation 17]

[0027]

[Equation 18]

[0028]

[Formula 19]

[0029]

[Equation 20]

Therefore, at a relatively low applied magnetic field,
It can be seen that spins oriented in the direction perpendicular to the longitudinal direction largely contribute to magnetostriction, but spins inclined by 19.5 ° with respect to the longitudinal direction do not contribute to magnetostriction.

When the material is prestressed, as shown in FIG. 4, spins (Equations 21 and 22) inclined by 19.5 ° with respect to the longitudinal direction due to the inverse magnetostrictive effect are generated in the direction perpendicular to the longitudinal direction (Equations 23 and 23). Turn to <111>). That is, in the optimum prestressed state, all spins are oriented in the direction perpendicular to the longitudinal direction. In this state, the relative amount of spins oriented in the direction perpendicular to the longitudinal direction is larger than in the state without prestress. Therefore, when a magnetic field is applied in the longitudinal direction, all the spins oriented in the direction perpendicular to the longitudinal direction change their orientations by 19.5 ° with respect to the longitudinal direction at once, so that a huge magnetostriction occurs. This phenomenon is <111
It is also observed in the giant magnetostrictive material grown to>, and it is called a magnetostrictive jump. However, in the metallographic structure of the giant magnetostrictive material, if a different phase or a heterogeneous phase exists, the magnetostrictive characteristics will not be improved even if such prestress is applied.

[0032]

[Equation 21]

[0033]

[Equation 22]

[0034]

[Equation 23]

The heat treatment of the giant magnetostrictive material removes the heterogeneous phase to obtain the phase equilibrium and make the structure uniform, so that the effect of prestress appears and the magnetostrictive characteristic is improved. For this method,
A method of performing heat treatment at 900 to 1100 ° C. for 5 to 7 days is known. Further, recently, as a heat treatment method which is an alternative to the former for homogenizing the structure, a heat treatment method of holding at 800 to 1100 ° C. for 20 minutes to 60 hours (Japanese Patent Laid-Open No. 1-12).
No. 3021), 0.5-1 at 1100-1200 ° C.
0.5 to 20 hours at 825 to 1100 ° C after holding for 0 hours
A method of performing a two-stage heat treatment of r (Japanese Patent Laid-Open No. 1-176024) has been proposed. The above is a heat treatment method for homogenizing the structure by removing the heterogeneous phase and obtaining phase equilibrium.

On the other hand, as a similar heat treatment method, recently, after the above-described heat treatment for homogenizing the tissue, a magnetic field is applied in the longitudinal direction and heated to a Curie temperature (450 ° C.) or higher, and then the magnetic field is applied in the longitudinal direction. A heat treatment method of cooling while applying in a vertical direction has been proposed (USP. 4,
818, 304). This seems to be due to the reverse magnetic field effect that occurs when prestressed when cooled from a temperature above the Curie point (450 ° C) in a magnetic field while applying a magnetic field in the direction perpendicular to the long axis direction of the material. In addition, spin is
It is directed to the number 24 or <111> in the inside and frozen as it is. As a result, it is stated that when a magnetic field is applied to the magnetostrictive material, the magnetostriction increases (a magnetostrictive jump phenomenon occurs) at a low magnetic field without prestress.

[0037]

[Equation 24]

[0038]

However, the above-mentioned Japanese Unexamined Patent Application Publication No.
The methods of -1223021 and Japanese Patent Application Laid-Open No. 1-176024 use the magnetostriction of a magnetostrictive material, although the treatment time is shortened as a heat treatment for homogenizing the material structure and removing different phases and precipitates. In order to increase the size inside, there is a drawback that it is necessary to have a structure in which the magnetostrictive material is prestressed in advance.

Further, the method of USP 4,818,304 does not require pre-stressing of the magnetostrictive material during use, but it has a drawback that a large magnetic field generator is required for the heat treatment apparatus. Therefore, the present invention eliminates the above-mentioned problems of the prior art, it is not necessary to pre-stress the magnetostrictive material during the use of the magnetostrictive material, and the heat treatment apparatus does not require a large magnetic field generation device, and a large It is an object of the present invention to provide a method for manufacturing a magnetostrictive material that can obtain magnetostriction.

[0040]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies on a method of increasing the magnitude of magnetostriction of a magnetostrictive material manufactured by a unidirectional solidification method, and as a result, The inventors have found that the magnetostriction increases without applying a prestress only by performing a heating / cooling process while applying a compressive force in advance, and thus completed the present invention.

That is, according to the present invention, after the rare earth metal-transition metal magnetostrictive material produced by the unidirectional solidification method is homogenized, a compressive force is applied in the solidification direction to a temperature above the Curie point of the material. The gist is a method for producing a rare earth metal-transition metal-based magnetostrictive material, which comprises heating and cooling while applying a compressive force. And the rare earth metal - transition metal-based magnetostrictive material, RT _x system (R represents Y and one or more rare earth elements, T is the x represents Fe, Co, one of Ni 1.5 to 2. It represents 0.) It is applied to alloys.

[0042]

The structure and operation of the present invention will be described. The magnetostrictive material used in the present invention is an RT _x system (R represents Y and one or more kinds of rare earth elements, T represents one kind of Fe, Co and Ni, and x represents 1.5 to 2.0. It's an alloy,
For example, in addition to Tb _0.3 Dy _0.7 Fe ₂ , TbFe _{2 and the} like can be mentioned.

In order to increase the magnitude of magnetostriction of the giant magnetostrictive material, the spin may be frozen. That is, after homogenizing the magnetostrictive material produced by the unidirectional solidification method, in a state where a compressive force is applied in the solidification direction, the material is heated to a temperature above the Curie point and cooled in a state where a compressive force is applied. Since it is heated and cooled while the inverse magnetostrictive effect due to the compressive force is generated, the spin can be frozen in the direction perpendicular to the long axis direction. As a result, when a magnetic field is applied, a magnetostrictive jump phenomenon is observed without applying prestress, and the magnitude of magnetostriction of the material increases. The homogenization treatment is performed on the magnetostrictive material manufactured by the unidirectional solidification method at 900 to 1100 ° C.
Heat treatment for 5 to 7 days to make the crystal structure of the material uniform.

[0044]

EXAMPLES Examples of the present invention will be described, but the present invention is not limited thereto. Tb _0.3 Dy _0.7 Fe
A unidirectionally solidified magnetostrictive material having a diameter of 6 mm and a length of 10 mm was manufactured by an ingot lowering method in a plasma arc melting furnace using an alloy powder of _1.9 composition as a raw material. This was heat-treated at 1000 ° C. for 7 days, and the amount of magnetostriction was measured by the strain gauge method.

The compressive force was applied by using a high-temperature compression tester to raise the temperature to 400 ° C. in an argon atmosphere, pressurizing it to a predetermined compressive force, holding it at this temperature for 1 hour, and then applying the compressive force. Furnace cooling in this state (cooling rate at this time is 150 ° C /
It was hr. )did.

Further, as comparative examples, a material that has been heat-treated at 1000 ° C. for 7 days, a material that has been given only a pressure, 4
Material heated / cooled to 00 ° C, material heat-treated at 1000 ° C for 2 hours, heated to 450 ° C under magnetic field
The cooled material was prepared. Table 1 shows the magnitude of the obtained magnetostriction amount.

[0047]

[Table 1]

Based on these results, No. In all of the Nos. 1 to 4, an increase in magnetostriction value of 17% or more is obtained, and the magnetostriction value increases as the applied pressure increases. N
o. Since the 5 materials were not heated and cooled by applying only a pressing force, the spins could not be frozen, and an increase in the magnetostriction value could not be obtained. No. The six materials were heated to 450 ° C. and cooled while applying a magnetic field, and the increase rate of the magnetostriction value was 85% and 120%.
A magnetostriction of 0 ppm was obtained, and the performance almost similar to that of the method of the present invention was obtained.

[0049]

Since the present invention is constructed as described above, the magnetostrictive material produced by the unidirectional solidification method is homogenized, and then a compressive force is applied in the solidification direction. The spin can be frozen by heating to a temperature above the Curie point and cooling with a compressive force applied. Therefore, when a magnetostrictive material is used, it is possible to pre-stress the magnetostrictive material in advance or to obtain a material that generates a large magnetostriction without the need for a large magnetic field generator, which is extremely useful in industry.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a principle of improving magnetostriction by applying prestress to a magnetostrictive material.

FIG. 2 is an explanatory diagram of changes in magnetization due to domain wall movement in a room temperature and low magnetic field.

FIG. 3 is an explanatory diagram of a change in magnetization in a high magnetic field.

FIG. 4 is an explanatory diagram of a change in magnetization when prestressing is applied.

Claims (3)

[Claims] 1. A rare earth metal produced by a unidirectional solidification method.
A rare earth metal characterized by heating a transition metal-based magnetostrictive material to a temperature higher than the Curie point of the material with a compressive force applied in the direction of solidification, and then cooling with a compressive force applied after homogenizing the material. -A method for manufacturing a transition metal-based magnetostrictive material. 2. The rare earth metal-transition metal-based magnetostrictive material is an RT _x -based material (R represents Y and one or more rare earth elements, T represents one of Fe, Co and Ni, and x is 1.5. ~
Represents 2.0. ) The method for producing a rare earth metal-transition metal-based magnetostrictive material according to claim 1, which is an alloy. 3. The method for producing a rare earth metal-transition metal magnetostrictive material according to claim 1, wherein homogenization treatment is performed at 900 to 1100 ° C. for 5 to 7 days.