JP2005206868A - Method for heat-treating super magnetostrictive material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively manufacture a magnetostrictive material with superior characteristics. <P>SOLUTION: The method for heat-treating the super magnetostrictive material includes mounting a molded article containing at least one rare earth element and a transition metal on a holder for heat treatment, and heat-treating (for example, sintering) the molded article. The holder for heat treatment is formed of an oxide of at least one element among the rare earth elements included in the molded article, as a main component. For instance, the rare earth elements included in the molded article are Tb and Dy, and the oxide of the rare earth element contained in the holder for heat treatment is Dy<SB>2</SB>O<SB>3</SB>. Because the oxide of the rare earth element used in the molded article is employed as the main component of the holder for heat treatment, a reaction during heat treatment (sintering) between the holder for heat treatment and the molded article is inhibited. The holder for heat treatment preferably has a relative density of 80% or higher. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat treatment method for a magnetostrictive material suitable for application to, for example, a method for sintering a magnetostrictive material in which a compact of an alloy powder is placed on a sintering jig and sintered.

  A giant magnetostrictive material made of a Tb-Dy-Fe intermetallic compound or the like has higher magnetostriction characteristics than conventional ferrite-based magnetostrictive materials and the like, and in recent years, its demand tends to increase more and more. Specific applications include linear actuators, vibrators, pressure torque sensors, vibration sensors, gyro sensors, and the like. When used in a linear actuator, a vibrator, or the like, the magnetostrictive element changes its size in accordance with the change in the applied magnetic field and generates a driving force. When used in a pressure torque sensor, vibration sensor, gyro sensor, or the like, the magnetostrictive element changes its magnetic permeability with a change in force applied from the outside, and pressure, torque, vibration, etc. are detected by sensing this.

  As a manufacturing method of such a giant magnetostrictive material, it has been conventionally known that a single crystal growth method is effective, but the single crystal growth method is extremely low in productivity and the degree of freedom of shape is greatly limited. There is a disadvantage that. Therefore, the powder metallurgy method is currently employed because it improves the disadvantages of the single crystal growth method and enables low-cost production. Basically, the sintered body by the powder metallurgy method weighs and mixes the raw material alloy powder, press-molds it into a predetermined shape, sinters the obtained compact, and performs post-processing if necessary. It is manufactured by applying.

However, when the powder metallurgy method is adopted for the production of the magnetostrictive material, it is a problem to increase the density of the sintered body, and a technique for that purpose has been proposed (for example, see Patent Document 1). In the invention described in Patent Document 1, a part of the raw material of the sintered body (Dy and Fe) is preliminarily subjected to hydrogen storage treatment, and another part of the raw material of the sintered body (Fe) is preliminarily reduced. By using a mixed gas of hydrogen gas and inert gas as the atmosphere in the sintering furnace during sintering, a dense sintered body can be obtained as compared with the case of sintering in an inert gas atmosphere alone. I have to. If the magnetostrictive material is a high-density sintered body, deterioration in characteristics such as magnetostriction characteristics in high-temperature air can be reduced.
JP 2003-3203 A

By the way, when sintering a molded body that is a raw material of the magnetostrictive material, generally, a sintering jig such as a setter, a sheath, a tray, or a mortar is used, and the molded body is placed on the sintering jig. In the mounted state, sintering is performed in a vacuum atmosphere, an inert gas atmosphere, or a reducing gas atmosphere. Conventionally, carbon, ZrO ₂ , Al ₂ O ₃ , SiO _{2 and the} like have been widely used as constituent materials for sintering jigs.

  At this time, since the sintering jig is in direct contact with the molded body during sintering, the constituent material constituting the sintering jig has heat resistance, does not react with the molded body during sintering, and is deformed into a molded body. It is required to have characteristics such as preventing the occurrence of heat and having high mechanical strength.

However, the above-described materials conventionally used for sintering jigs have high reactivity with a molded body when sintered in a vacuum atmosphere, an inert gas atmosphere, or a reducing gas atmosphere, and thus can be obtained. There is a problem of deteriorating the characteristics of the magnetostrictive material produced. For example, carbon may react with the constituent material of the molded body to deteriorate the characteristics of the magnetostrictive material. In addition, ZrO ₂ , Al ₂ O _{3 and the} like have a problem that they easily adsorb impurity gas such as oxygen gas, moisture gas, carbon dioxide gas on the surface because they are porous, and this impurity gas is released during sintering. As a result, the rare earth element is oxidized to produce a rare earth element oxide. For this reason, the characteristic of a magnetostrictive material will deteriorate significantly. SiO ₂ is a relatively good material as a sintering jig, but has disadvantages such as easy cracking, and is also very expensive and expensive to manufacture.

  The present invention has been proposed in view of such conventional circumstances, and can suppress the reaction between the molded body and the heat treatment jig and the release of residual gas from the heat treatment jig, and has excellent magnetostriction. It is an object of the present invention to provide a heat treatment method for a magnetostrictive material capable of inexpensively performing material production (heat treatment, sintering, etc.).

  In order to achieve the above-described object, the magnetostrictive material heat treatment method of the present invention includes a magnetostriction in which a molded body containing at least one rare earth element and a transition metal is placed on a heat treatment jig, and the molded body is heat treated. A heat treatment method for a material, wherein the heat treatment jig is composed mainly of at least one oxide of rare earth elements contained in the compact.

  In the present invention, it is important to match the types of rare earth elements in the rare earth element contained in the compact to be heat treated and the rare earth element oxide contained in the jig for heat treatment on which the compact is placed. . By using at least one oxide among the rare earth elements used in the molded body as the main component of the heat treatment jig, the reaction between the heat treatment jig and the molded body during sintering is reliably suppressed. As a result, characteristic deterioration in the magnetostrictive material is suppressed. In addition, since rare earth element-containing oxides have high mechanical strength and are relatively inexpensive, a sintering jig using this rare earth element as a main component not only suppresses reaction with the molded body, but also mechanical strength. Excellent heat resistance and enables low-cost production of magnetostrictive materials.

  Furthermore, in the heat treatment method of the magnetostrictive material of the present invention, in addition to the above structure, the relative density of the heat treatment jig is 80% or more, which is an additional structural requirement. And the release of residual gas is suppressed. In addition, the heat treatment jig is easily cracked in a vacuum, an inert gas atmosphere, or a reducing gas atmosphere, but by using the relative density, the strength is improved and cracking is also eliminated.

  In addition, the heat treatment in the present specification is a concept including all heat treatments for heat-treating a molded body, and includes firing and sintering accompanied by a chemical reaction.

  According to the heat treatment method of a magnetostrictive material of the present invention, since the heat treatment jig on which the formed body is placed is composed of the same rare earth element oxide as the rare earth element contained in the formed body, heat treatment such as during sintering is performed. The reaction between the jig for heat treatment and the molded body at the time can be suppressed, and a magnetostrictive material having excellent characteristics can be manufactured. Further, according to the heat treatment method for a magnetostrictive material of the present invention, since the jig for heat treatment having high mechanical strength, heat resistance and low cost is used, the manufacturing cost of the magnetostrictive material can be reduced.

  Furthermore, according to the heat treatment method of the magnetostrictive material of the present invention, by setting the relative density of the heat treatment jig to 80% or more, it is possible to suppress the release of residual gas from the heat treatment jig, and to crack the heat treatment jig. Etc. can also be eliminated, and further effects can be obtained in improving the characteristics of the obtained magnetostrictive material and reducing the manufacturing cost.

  Hereinafter, a heat treatment method for a magnetostrictive material to which the present invention is applied will be described in detail with reference to the drawings. Here, the case where an alloy (metal) powder is pressure-molded and then the molded body is placed on a heat treatment jig and sintered will be described as an example, but the present invention is limited to sintering. However, it goes without saying that it can be applied to heat treatment in general.

First, a magnetostrictive material manufactured by the heat treatment method (sintering method) of this embodiment will be described. The magnetostrictive material manufactured using the powder metallurgy method is, for example, RT _y (where R is one or more rare earth elements, T is one or more transition metals, and y is 1 <y <4. It is obtained by sintering an alloy powder having a composition represented by

  Here, R represents at least one selected from lanthanoid series and actinoid series rare earth elements including Y. Among these, R is preferably a rare earth element such as Nd, Pr, Sm, Tb, Dy, or Ho, more preferably Tb or Dy, and these can be used in combination. T represents one or more transition metals. Among these, as T, transition metals such as Fe, Co, Ni, Mn, Cr, and Mo are particularly preferable, and these can be mixed and used.

Of the alloys represented by RT _y , the RT ₂ Laves type intermetallic compound with y = 2 has a high Curie temperature and a large magnetostriction value, and therefore is suitable for a magnetostrictive element. Here, when y is 1 or less, the RT phase is precipitated by the heat treatment after sintering, and the magnetostriction value is lowered. When y is 4 or more, the RT ₃ phase or the RT ₆ phase increases and the magnetostriction value decreases. Therefore, in order to RT ₂ is more rich phase, y is 1 <range of y <4 is preferable.

R may be a mixture of two or more rare earth elements, and it is particularly preferable to use a mixture of Tb and Dy. Specifically, in the alloy represented by Tb _a Dy _(1-a) , a is more preferably in the range of 0.27 <a ≦ 0.50. As a result, (Tb _a Dy _(1-a) ) T _y alloy has a large saturation magnetostriction constant and a large magnetostriction value. Here, when a is 0.27 or less, a sufficient magnetostriction value is not exhibited at room temperature or less, and conversely when it exceeds 0.50, a sufficient magnetostriction value is not exhibited near room temperature.

T is particularly preferably Fe, and Fe forms Tb, Dy and (Tb, Dy) Fe ₂ intermetallic compound, and a sintered body having a large magnetostriction value and high magnetostriction characteristics is obtained. At this time, a part of Fe may be replaced by Co or Ni, but Co increases magnetic anisotropy, but lowers the magnetic permeability, and Ni lowers the Curie temperature. Reduce the magnetostriction value at high magnetic field. Therefore, Fe is preferably 70% by weight or more, and more preferably 80% by weight or more.

  Next, the manufacturing method of a magnetostrictive material is demonstrated. FIG. 1 shows an example of a manufacturing process of a magnetostrictive material (sintered body) by a powder metallurgy method. As shown in FIG. 1, the magnetostrictive material is basically obtained by pre-treating three kinds of raw materials A, B, and C, respectively, and then undergoing processes such as weighing, mixing and grinding, molding, and sintering. Manufactured.

The raw material A, which is a part of the raw material, is subjected to heat treatment (annealing) on a Tb—Dy—Fe-based alloy having a predetermined composition and then pulverized. An alloy having a composition of Dy ₂ Fe as the raw material B is pulverized after hydrogen storage. As the raw material C, a reduction process is performed to remove oxygen from Fe in a hydrogen gas atmosphere.

Here, it is preferable that a part of these alloy powders be subjected to hydrogen storage treatment. By storing hydrogen in the alloy powder, distortion occurs and cracks occur due to the internal stress. For this reason, the mixed alloy powder is subjected to pressure when forming a compact, and is pulverized inside to become fine, and a dense high-density sintered body can be obtained when sintered. Furthermore, since rare earth elements such as Tb and Dy are easily oxidized, an oxide film having a high melting point is formed on the surface even if there is a slight amount of oxygen to suppress the progress of sintering, but by storing hydrogen, There is also an advantage that oxidation is difficult. The alloy powder to be subjected to hydrogen storage treatment is preferably represented by, for example, Dy _b T _(1-b) , and has a composition in which b is 0.37 ≦ b ≦ 1.00. In the formula, T may be Fe alone or a part of Fe may be substituted with Co or Ni. Therefore, among the aforementioned raw materials, it is optimal to use the raw material B as an alloy powder that is subjected to hydrogen storage treatment.

Next, a predetermined amount of the above-mentioned raw material A, raw material B and raw material C are weighed, pulverized and mixed, and molded in a magnetic field to produce a molded body. At this time, the composition of the raw material alloy powder after mixing is, for example, Tb _0.3 Dy _0.7 Fe _1.88 .

  Subsequently, the compact is put in a sintering furnace, heat-treated under predetermined conditions, and sintered to produce a sintered compact. Sintering is performed by going through a temperature rising process in which the molded body is heated to a predetermined temperature after being placed in a sintering furnace, a process in which the predetermined temperature (stable temperature) is kept substantially constant, and a temperature lowering process.

  It is preferable to perform the temperature increase rate in the temperature increase process at 3 to 20 ° C./min. If the heating rate is less than 3 ° C./min, the productivity is low, and if the heating rate exceeds 20 ° C./min, the temperature of the raw material powder formed in the furnace is not uniform, and segregation or heterogeneous phase may occur. It is.

The stable temperature is preferably in the range of 1150 to 1240 ° C. If the stable temperature is less than 1150 ° C., a long stabilization time is required to remove internal strain, resulting in inefficiency. Conversely, if the stable temperature exceeds 1240 ° C., the melting point of the alloy represented by RT _y This is because the sintered body itself may be melted and a different phase such as the RT ₃ phase may be precipitated.

  The sintering atmosphere is basically an inert gas atmosphere using an inert gas such as argon gas alone, but hydrogen gas is introduced into the sintering furnace along with the inert gas during the sintering process. By doing so, it is preferable to carry out a part of the sintering in a mixed atmosphere containing hydrogen gas and inert gas. Specifically, first, the temperature in the sintering furnace is raised as an inert gas alone atmosphere, thereby completely releasing hydrogen gas contained in the compact (such as raw material alloy powder subjected to hydrogen storage treatment). Next, the introduction of hydrogen gas is started, and the raw material alloy powder is activated by setting the inside of the sintering furnace to a mixed gas atmosphere of hydrogen gas and inert gas. Here, the mixed gas atmosphere of hydrogen gas and inert gas is important for increasing the density of the sintered body. Finally, the introduction of hydrogen gas is stopped, and the inside of the sintering furnace is again brought to an inert gas alone atmosphere to complete the sintering.

  During the above sintering process, at least one of the temperature range of 650 ° C. or higher and the stable temperature range of 1150 ° C. or higher and 1240 ° C. or lower in the temperature rising process is a mixed gas atmosphere of hydrogen gas and inert gas in the sintering furnace. To do. Specifically, when hydrogen gas: argon (Ar) gas = X: 100-X, X (volume%) is preferably 0 <X <50. Since argon gas is an inert gas and does not oxidize the rare earth element R, it can be mixed with hydrogen gas to obtain an atmosphere having a reducing action. In order to obtain a reducing action, X (volume%) is preferably made larger than 0, and when hydrogen gas becomes excessive, the reducing action is saturated, so X <50 is preferred. In addition, in a temperature range of 650? Or more in the temperature rising process, a mixed gas atmosphere of hydrogen gas and inert gas can be used to prevent oxidation due to a small amount of remaining oxygen.

  In particular, for the temperature and atmosphere control during sintering, as shown in FIG. 2, it is preferable that the introduction start temperature of hydrogen gas is 900 ° C. to 1000 ° C., and the end temperature of introduction of hydrogen gas is 1150 ° C. It is preferable to set it as 1200 degreeC. Furthermore, it is more preferable that 10 <X <50 when the mixing ratio of hydrogen gas and argon gas is expressed as hydrogen gas: argon (Ar) gas = X: 100-X by volume ratio.

  Although it is conceivable that all sintering is performed in an inert gas atmosphere alone, it is difficult not only to increase the density with an inert gas alone, but also to completely remove oxygen. The characteristics are greatly reduced. The rare earth element R reacts very easily with oxygen to form a stable rare earth oxide, but this rare earth oxide has low magnetism but does not exhibit magnetic properties that make it a practical magnetic material. It is. Therefore, from the viewpoint of preventing oxidation of rare earth elements, it is preferable to perform sintering in a mixed gas atmosphere of hydrogen gas and inert gas. Further, the atmosphere during sintering can be arbitrarily changed depending on the object to be sintered, and for example, a vacuum atmosphere may be used.

In the present invention, when the compact is sintered, the heat treatment jig (sintering jig) 1 and the compact 2 are combined as shown in FIG. The heat treatment jig 1 used here contains at least one rare earth element oxide as a main component among the rare earth elements contained in the compact 2. For example, when the molded body 2 is a molded body formed by molding a raw material alloy powder of a Tb-Dy-Fe rare earth intermetallic compound, the sintering jig 1 mainly contains at least one oxide of Tb and Dy. In this case, it is preferable to contain Dy ₂ O ₃ which is an oxide of Dy as a main component. A heat treatment jig mainly composed of an oxide of a rare earth element can be manufactured by a dry forming method, which is a simple manufacturing method, and is inexpensive. In FIG. 3, a setter having a recess for placing the molded body 2 is illustrated as the heat treatment jig 1, but the heat treatment jig used in the present invention is not limited to a setter, but a sheath, a tray, A bowl etc. may be sufficient.

As described above, by performing sintering by combining a molded body containing a rare earth element and a jig for heat treatment containing an oxide of at least one rare earth element of the rare earth element contained in the molded body, There is no possibility that the jig for heat treatment reacts at the time of sintering to adversely affect the molded body, and a magnetostrictive material with small characteristic deterioration can be obtained. In addition, heat treatment jigs mainly composed of rare earth oxides are less expensive than heat treatment jigs mainly composed of SiO ₂ , so that magnetostrictive materials can be manufactured at low cost. it can. Further, a heat treatment jig mainly composed of an oxide of a rare earth element also has an advantage of excellent mechanical strength and heat resistance.

  The relative density of the heat treatment jig to be used is preferably 80% or more from the viewpoint of preventing the molded body from being contaminated by the impurity gas released from the heat treatment jig. More preferably, the relative density is 90% or more. When the relative density is less than 80%, the porosity is increased, and the heat treatment jig easily adsorbs moisture gas, oxygen gas, and carbon dioxide gas in the atmosphere. As a result, the impurity gas adsorbed in the vacuum atmosphere during the sintering or the reducing gas atmosphere is released, which may contaminate the molded body and cause deterioration of characteristics.

  In view of improving the mechanical strength of the heat treatment jig, the relative density of the sintering jig is preferably 80% or more. Heat treatment jigs are easily cracked in sintering in a vacuum atmosphere, inert gas atmosphere, or reducing gas atmosphere. Therefore, in order to obtain mechanical strength that prevents cracking during sintering, the heat treatment jig The relative density is preferably 80% or more, and more preferably 90% or more.

  Next, specific examples of the present invention will be described based on experimental results.

<Sintering of magnetostrictive material>
In this example, a compact of Tb—Dy—Fe-based raw material alloy powder was placed on a heat treatment jig and sintered to produce a magnetostrictive material. The produced magnetostrictive material is a magnetostrictive material made of a Tb—Dy—Fe-based intermetallic compound.

First, the raw material A was subjected to heat treatment (annealing) on a Tb—Dy—Fe-based alloy having a predetermined composition and then pulverized. An alloy having a composition of Dy ₂ Fe as the raw material B was subjected to hydrogen storage treatment and then pulverized. As the raw material C, Fe was subjected to a reduction treatment for removing oxygen in a hydrogen gas atmosphere.

Next, each of the obtained raw materials A, B, and C was weighed and then pulverized and mixed to obtain a raw material alloy powder having an overall composition of Tb _0.3 Dy _0.7 Fe _1.88 . The obtained raw material alloy powder was put in a mold and molded in a magnetic field of 8 kOe to obtain a molded body. The molded body was cylindrical, and had a diameter of 6 to 10 mm and a length of 30 mm.

Next, as shown in FIG. 4, the molded body 12 was placed on a flat plate heat treatment jig 11 and sintered. The external dimensions of the heat treatment jig 11 are 30 mm × 40 mm × 5 mm (thickness t). In the sintering, the molded body 12 was placed on the heat treatment jig 11 and heated, and fired in a stable temperature section of 1150 ° C. to 1240 ° C. to obtain a sintered body. Sintering was performed in three types of atmospheres: vacuum firing, reducing gas atmosphere (H ₂ / Ar gas), and inert gas atmosphere (Ar gas).

<Difference in characteristics depending on the material of the heat treatment jig>
According to the sintering method described above, the molded body 12 was sintered by changing the material of the heat treatment jig 11. As the material of the heat treatment jig 11, carbon, ZrO ₂ , Al ₂ O ₃ , MgO, which is a material system that does not contain a rare earth (a material system different from the molded body), and Tb ₄ O ₇ − which is a rare earth element-containing oxide are used. Dy ₂ O ₃ composite oxide, Dy ₂ O ₃ .

  Table 1 shows whether or not the magnetostrictive characteristics (1 kOe) and characteristic standard values of the magnetostrictive material obtained using the heat treatment jig made of a material system that does not contain rare earths are satisfied. Similarly, Table 2 shows whether the magnetostrictive characteristics (1 kOe) and characteristic standard values of the magnetostrictive material obtained using the heat treatment jig made of the rare earth element-containing oxide are satisfied. Whether or not the characteristic standard value is satisfied is based on 1000 ppm, and when it is more than this, it is OK, and when it is less than 1000 ppm, it is NG.

As is apparent from Table 1, when a jig for heat treatment of a material system that does not contain a rare earth, which is a material system different from the molded body (magnetostrictive material), is used, both have low magnetostriction characteristics and satisfy characteristic specification values. Nothing was seen. On the other hand, as is clear from Table 2, Tb ₄ O ₇ —Dy ₂ O ₃ composite oxide and Dy ₂ O, which are oxide materials of the same rare earth element as one of the rare earth elements contained in the compact. _When the heat treatment jig constituted by ₃ was used, it was confirmed that the characteristic deterioration of the magnetostrictive material was not observed and the characteristic standard value was satisfied. Further, when Tb ₄ O ₇ —Dy ₂ O ₃ composite oxide and Dy ₂ O ₃ were compared, a better effect was obtained with Dy ₂ O ₃ .

It is a flowchart which shows an example of the manufacturing process of the sintered compact of this invention. It is a schematic diagram for demonstrating the time-dependent change and atmosphere of sintering temperature at the time of sintering. It is a schematic sectional drawing for demonstrating the sintering method of the magnetostrictive material of this invention. It is a schematic sectional drawing which shows the sintering state in an Example.

Explanation of symbols

1,11 Jig for heat treatment, 2,12 Molded body

Claims (6)

A magnetostrictive material heat treatment method comprising placing a molded body containing at least one rare earth element and a transition metal on a heat treatment jig, and heat-treating the molded body,
The heat treatment method for a magnetostrictive material, wherein the heat treatment jig is composed mainly of at least one oxide of rare earth elements contained in the compact. _{2. The} method for heat-treating a magnetostrictive material according to claim 1, wherein the rare earth element contained in the compact is Tb and Dy, and the oxide of the rare-earth element constituting the heat treatment jig is Dy ₂ O _3. .   3. The heat treatment method for a magnetostrictive material according to claim 1, wherein the heat treatment is performed in any one of a vacuum, an inert gas atmosphere, and a reducing gas atmosphere.   The method for heat treatment of a magnetostrictive material according to any one of claims 1 to 3, wherein a relative density of the heat treatment jig is 80% or more.   5. The heat treatment method for a magnetostrictive material according to claim 4, wherein the relative density is 90% or more.   6. The method for heat treatment of a magnetostrictive material according to claim 1, wherein the heat treatment is sintering or firing.

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