JP2005200753A - Tool for heat treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tool for heat treatment with which gas exhausted from a molding can quickly removed and dense sintered compact can be produced. <P>SOLUTION: This tool for heat treatment is the tool for laying the molding formed of raw material alloy powder containing rare earth metal elements and transition metal elements at the heat treatment time. A V-shaped cross sectional groove part for positioning the molding, is formed on the laying surface of the molding, and an escaping groove enlarging the cross sectional area of the groove part, is formed along the bottom part of the groove part. An angle (angle of the V groove) formed by the inner wall surfaces of the groove part is about 90° and for example, this tool is suitably applied to the sintering of magnetostrictive material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat treatment jig (so-called setter) used when, for example, a sintered compact of an alloy powder is sintered.

  Magnetostrictive materials made of Tb-Dy-Fe-based intermetallic compounds and the like have higher magnetostrictive properties than conventional ferrite-based magnetostrictive materials and the like, and in recent years, their 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 method for producing such a magnetostrictive material, it has hitherto been 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 drawback. 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.

  By the way, when sintering the compact, a heat treatment jig generally called a setter is used, and the compact is placed on the heat treatment jig in a vacuum atmosphere or an inert gas atmosphere. Alternatively, sintering (heat treatment) is performed in a reducing gas atmosphere. At this time, since the jig for heat treatment is in direct contact with the molded body during sintering, the constituent material constituting the jig has heat resistance, does not react with the molded body during sintering, and the molded body is not deformed. Characteristics such as not causing it to occur and having high mechanical strength are required.

  FIG. 9 shows an example of a setter used when, for example, a cylindrical shaped body is sintered. When the cylindrical shaped body 102 is sintered, a setter 101 having a frame-like edge with a high height around it is used to prevent rolling. As a method of arranging the compacts, measures such as placing the compacts having relatively short lengths and arranging the compacts separately to prevent adhesion of the compacts are taken.

However, such an arrangement has a disadvantage that bending occurs in the case of a molded body having a longer dimension and a smaller diameter. For this reason, the use of a V-groove setter having a V-shaped groove formed on the surface has also been proposed (see, for example, Patent Document 1). If a groove having a V-shaped cross section is formed and an elongated molded body is positioned by this groove, it is possible to reliably prevent bending.
Japanese Patent Laid-Open No. 2003-119083

  However, conventionally, the shape of the V-groove formed on the surface of the setter has not been studied, and a sintered body of sufficient quality is not necessarily obtained particularly in sintering of a magnetostrictive material. In the sintering of the magnetostrictive material, it is necessary to degas from the inside in order to prevent the reaction with the setter and to sinter densely. In particular, when the diameter of the molded body is 10 mm or more, it is difficult for gas to escape from the inside, and the sintered density tends not to increase. Therefore, it is desirable to minimize the contact area between the molded body and the setter, to ensure the maximum area for gas release, and to quickly release the gas released from the molded body.

  The present invention has been proposed in view of such a conventional situation, and an object thereof is to optimize a groove shape formed in a setter (heat treatment jig). That is, the present invention provides a heat treatment jig capable of minimizing the reaction with the molded body and quickly removing the gas that has escaped from the molded body. It aims at providing the jig for heat processing which can manufacture a body (magnetostrictive material).

  In order to achieve the above-described object, the heat treatment jig of the present invention is a heat treatment jig on which a formed body obtained by forming a raw material alloy powder containing a rare earth element and a transition metal element is placed during the heat treatment. A groove portion having a V-shaped cross-section for positioning the molded body is formed on the mounting surface of the, and a relief groove is formed along the bottom of the groove portion to enlarge the cross-sectional area of the groove portion.

  Since the jig for heat treatment of the present invention has a groove having a V-shaped cross section formed on the surface thereof, a cylindrical or cylindrical shaped body is positioned by this groove, and the occurrence of bending during sintering is suppressed. The At the same time, by forming a relief groove that expands the cross-sectional area of the groove portion along the bottom portion of the groove portion, the degassing from the groove portion is smoothly performed, and the outgassing from the molded body is promoted to be a dense sintered body. Is realized.

  In the groove portion having a V-shaped cross section, the angle formed by the inner wall surface (opening angle of the V groove) is appropriate in the vicinity of 90 ° where the load is evenly distributed, and thereby the contact area with the molded body is minimized. The Moreover, by standardizing to the said angle, the jig | tool for heat processing is standardized and it is advantageous also on the point of economical efficiency and management.

  According to the heat treatment jig of the present invention, the reaction with the molded body can be minimized, and the gas escaped from the molded body can be quickly eliminated. Therefore, by performing heat treatment, for example, sintering using the heat treatment jig of the present invention, a dense and high-quality sintered body (for example, magnetostrictive material) is manufactured without causing characteristic deterioration or deformation due to reaction. Is possible.

  Hereinafter, a heat treatment jig (setter) to which the present invention is applied will be described in detail with reference to the drawings. In the following, an example of a heat treatment jig used for sintering a magnetostrictive material (giant magnetostrictive material) containing a rare earth element and a transition metal element will be described. However, the present invention is not limited to this. Needless to say.

First, a magnetostrictive material manufactured by a powder metallurgy method using the heat treatment jig of the present invention will be described. The magnetostrictive material manufactured by the powder metallurgy method is, for example, RT _y (where R is one or more rare earth elements, T is one or more transition metal elements, 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 metal elements. 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.

The rare earth element R may be a mixture of two or more rare earth elements. In particular, it is 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.

The transition metal element T is particularly preferably Fe. Fe forms a 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. 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 above-described sintering, the molded body is placed on a heat treatment jig called a setter, and sintering, which is a kind of heat treatment, is performed. The heat treatment jig used at this time is basically a heat treatment jig 1 in which a V-shaped groove 2 having a V-shaped cross section is formed on the surface as shown in FIG. The columnar shaped body 3 is placed on the heat treatment jig 1 in a state of being dropped into each V-groove 2 and sintered. Accordingly, each molded body 3 is positioned by the V-groove 2 and no bending occurs during sintering.

  Further, as shown in FIG. 4, the V-groove 2 is formed such that the angle formed by the inner wall surface is approximately 90 °. An appropriate angle of the V groove 2 is around 90 ° where the load is uniformly distributed. By setting the angle of the V-groove 2 in the vicinity of 90 °, the contact state between the molded body 3 and the heat treatment jig 1 can be optimized, the contact area can be minimized, and the molded body 3 can be used for heat treatment. Reaction with the jig 1 can be prevented.

  By setting the angle of the V groove 2 to 90 ° and using it as a standard, the heat treatment jig 1 can be standardized. For example, if the shape of the V-groove 2 is equal to or less than the designed diameter, it can be applied to the molded body 3 having a different diameter. Further, the molded body 3 outside the above range can be dealt with by simply changing the depth of the V-groove 2, and the other design does not need to be changed. For example, in the example shown in FIG. 4, the thickness T of the heat treatment jig 1 is 8 mm and the depth d of the V groove 2 is 3.5 mm, but the thickness of the heat treatment jig 1 and the depth of the V groove 2 are the same. It is possible to cope with the molded bodies 3 of different sizes simply by changing the above. Such standardization of the heat treatment jig 1 is not only economical, but also easy to manage.

  Furthermore, in the heat treatment jig 1 of the present invention, as shown in FIG. 5, a rectangular relief groove 4 is provided at the bottom (V-shaped apex portion) of the V groove 2 to enlarge the sectional area of the groove. I am doing so. When the molded body 3 is sintered, smooth degassing from the molded body 3 is important for obtaining a dense sintered body. In particular, when the diameter of the molded body 3 is 10 mm or more, it is difficult for gas to escape from the inside, and the sintered density tends not to increase.

  Therefore, it is desired to promptly escape the gas that has escaped from the molded body 3 and promote gas escape from the inside. At this time, in particular, gas escape from the space below the molded body 3 becomes a problem. As shown in FIG. 3, when a cylindrical shaped body 3 is dropped into the V groove 2, a substantially triangular space S <b> 1 exists below the shaped body 3. Accordingly, the gas escaped from the molded body 3 escapes from the space S1. In order to promote the escape of gas, it is necessary to secure the largest possible cross-sectional area of the space S1. However, the mere V groove 2 has a limit in the cross-sectional area of the space S1 to be formed.

  Therefore, in the heat treatment jig 1 of the present invention, as described above, the rectangular relief groove 4 is provided at the bottom of the V groove 2 so as to enlarge the cross-sectional area of the groove. FIG. 6 is an enlarged view of the bottom of the V groove 2. By providing the escape groove 4, the cross-sectional area of the space below the molded body 3 is expanded to space S <b> 1 + space S <b> 2. Thus, by expanding the space for degassing, a dense sintered body can be obtained and the quality of the magnetostrictive material can be improved.

  The shape of the escape groove 4 is not limited to a rectangle and is arbitrary, and its depth, width, etc. are also arbitrary. Although the cross-sectional area expanded by increasing the width of the escape groove 4 increases, restrictions are imposed on the size of the molded body 3 that can be accommodated by the V-groove 2, so that it is preferable to determine in consideration of this point. Further, the depth of the escape groove 4 is preferable because the ratio of the cross-sectional area that is enlarged by increasing the depth as much as possible is preferable. For example, the escape groove 4 can be formed so as to penetrate the heat treatment jig 1. However, in this case, the strength of the heat treatment jig 1 is lowered, so care must be taken.

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

<Sintering of magnetostrictive material>
In this example, a compact of a Tb-Dy-Fe-based raw material alloy powder was sintered to produce a magnetostrictive material composed 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.

Next, sintering was performed in a sintering furnace. For the sintering, the temperature of the sintering furnace was increased and firing was performed in a stable temperature range of 1150 ° C to 1240 ° C to obtain a sintered body. In accordance with the profile shown in FIG. 2, the sintering atmosphere starts introduction of hydrogen at 900 to 1000 ° C. and finishes introduction of hydrogen at 1150 to 1200 ° C. H ₂ / Ar gas).

<Preliminary experiment>
According to the sintering method described above, the relationship between the diameter φ of the cylindrical shaped body and the sintering density was examined. The heat treatment jig used is a heat treatment jig having a V groove shown in FIG. The size of the heat treatment jig is 60 mm × 40 mm, the thickness is 8 mm, and the depth of the V groove is 3.5 mm.

  FIG. 7 shows the relationship between the diameter φ of the sintered compact and the sintered density of the obtained sintered body. As is apparent from FIG. 7, when the diameter exceeds 10 mm, the sintered density is significantly reduced. In the present example, the pass line for the sintered density is set to 95.0%.

<Confirmation of effect by escape groove>
Based on the result of the preliminary experiment, a molded body having a diameter of 10 mm and a molded body having a diameter of 12 mm were sintered using a heat treatment jig provided with a relief groove. FIG. 8 shows the relationship between the sintering density and the expansion ratio of the space due to the clearance groove (the ratio of the sectional area of the space expanded by forming the clearance groove with the sectional area of the space of only the V groove being 100%). .

  By forming relief grooves and expanding the cross-sectional area of the space, the sintering density is increased. In particular, by setting the expansion ratio of the space to 140% or more, the sintered density reaches the pass line even in the molded body having a diameter of 12 mm.

It is a flowchart which shows an example of the manufacturing process of a sintered compact. It is a schematic diagram which shows the sintering temperature at the time of sintering, and the profile of atmosphere. It is a schematic perspective view which shows an example of the jig for heat processing which has V groove. It is a schematic sectional drawing which shows the appropriate angle of V groove. It is a schematic sectional drawing which shows an example of the jig | tool for heat processing which formed the escape groove in the bottom part of V groove. It is a schematic sectional drawing which expands and shows the escape groove vicinity. It is a characteristic view which shows the relationship between the diameter (phi) of a molded object, and the sintered density of the obtained sintered compact. It is a characteristic view which shows the relationship between the expansion rate of the space by the escape groove and the sintered density. It is the perspective view which showed an example of the conventional setter.

Explanation of symbols

1 Heat treatment jig, 2 V groove, 3 molded body, 4 relief groove

Claims (6)

A heat treatment jig for mounting a molded body obtained by forming a raw material alloy powder containing a rare earth element and a transition metal element during heat treatment,
A groove having a V-shaped cross section for positioning the molded body is formed on the mounting surface of the molded body, and a relief groove is formed along the bottom of the groove to increase the cross-sectional area of the groove. A jig for heat treatment.   The heat treatment jig according to claim 1, wherein an angle formed by an inner wall surface of the groove portion having the V-shaped cross section is approximately 90 °.   The jig for heat treatment according to claim 1 or 2, wherein the shape of the escape groove is substantially rectangular in cross section.   The jig for heat treatment according to any one of claims 1 to 3, wherein a shape of the molded body to be placed is a columnar shape or a cylindrical shape. The raw material alloy powder has a composition represented by the general formula RT _y (wherein R is one or more rare earth elements, T is one or more transition metal elements, and 1 <y <4). The heat treatment jig according to claim 1, wherein the heat treatment jig is a heat treatment jig.   6. The jig for heat treatment according to claim 1, wherein the sintered body obtained by sintering the molded body is a magnetostrictive element.

Images