JP2946350B2 - Method for producing sintered body made of amorphous alloy powder - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sintered body made of amorphous alloy powder suitable for producing a magnetic component such as a torque sensor of an electric power steering device.

In this specification, the term "ceramic powder" refers to rocks, minerals, powders made of conventional ceramics such as porcelain made of silicates such as viscosities, as well as other oxides and powders. , Nitrides, carbides,
It is used to include powders of so-called new ceramics produced using synthetic materials such as borides and silicides under high pressure firing and other required conditions.

2. Description of the Related Art As a torque sensor of an electric power steering device, a torque sensor made of an amorphous alloy has been considered.
It is known that in order to improve the performance of a porcelain component such as a torque sensor, it is necessary to lower the porosity of the sintered body, in other words, to increase the density. When the porosity of the sintered body is high, the temperature dependence of the magnetic properties increases, and the stability of the porcelain properties is impaired. Moreover, when the density of the sintered body is low, there is a problem that the mechanical processing cannot be performed due to insufficient strength.

Conventionally, a sintered body made of an amorphous alloy powder has been manufactured by a hot press method, a rolling method, a hot extrusion method, an explosion molding method, or the like using a rapidly solidified amorphous alloy powder produced by a liquid quenching method. However, in the case of the hot press method, the density ratio of the sintered body to be manufactured is small, so that a high-density sintered body cannot be obtained. There is a problem that the density varies. In the case of the rolling method and the hot extrusion method, a high-density product can be obtained, but there is a problem that a large-sized sintered body having a thickness of 5 mm or more or a diameter of 10 mm or more cannot be produced. In addition, there is a problem that the density of the formed sintered body varies due to uneven load stress. In the case of explosive molding, there is a problem that cracks occur when a large-sized sintered body is formed. Furthermore, it is conceivable to manufacture sintered bodies by hot isostatic pressing (HIP), which is a powder metallurgy method suitable for manufacturing high-density sintered bodies. However, there is a problem that a sintered body cannot be manufactured because an oxide film is formed. As a result, there is a problem that it is not possible to obtain a high-density sintered body suitable for forming a magnetic component such as a torque sensor and suitable for processing. In addition, in order to manufacture a sintered body of a predetermined near net shape by HIP, a metal capsule having a complicated shape must be used, and it is extremely difficult to manufacture the capsule. There is a problem that it is not suitable for production.

An object of the present invention is to provide a method for manufacturing a sintered body made of an amorphous alloy powder, which solves the above problem.

Means for Solving the Problems A method for producing a sintered body made of an amorphous alloy powder according to the present invention comprises the steps of: encapsulating an amorphous alloy powder produced by a mechanical alloying method or a mechanical grinding method in a rubber or plastic capsule; It is compression molded into a near net shape by isostatic pressing, and the molded body is heated for a predetermined time in a temperature range of 100 ° C. lower than the crystallization temperature and lower than the crystallization temperature for a predetermined time, and then the capsule is heated in the above temperature range. The compression molding is performed by hot isostatic pressing without encapsulation in a time period in which the amorphous alloy does not crystallize.

Another method for producing a sintered body made of an amorphous alloy powder according to the present invention is as follows: an amorphous alloy powder produced by a mechanical alloying method or a mechanical grinding method is encapsulated in a rubber or plastic capsule, and is cold isostatically pressed. By compression molding into a near net shape, and then put the molded body in a larger metal capsule, fill the gap with ceramic powder as a secondary pressure medium, and then 100 ° C. below the crystallization temperature. The compression molding is performed by hot isostatic pressing in a temperature range from a low temperature to a crystallization temperature for a time during which the amorphous alloy does not crystallize.

In both of the above methods, the mechanical alloying method or the mechanical gliding method is performed using an apparatus such as a ball mill. That is, an amorphous alloy powder can be obtained by placing a mixed powder or alloy powder of a metal constituting the amorphous alloy in a container of a mill and rotating the agitator for a predetermined time in an inert gas atmosphere or a vacuum atmosphere. Since the mechanical alloying method and the mechanical grinding method are performed in an inert gas atmosphere or a vacuum atmosphere as described above, the powder surface is always formed as a new surface by repetition of destruction and cold welding. There is no oxide film on the surface of the amorphous alloy powder produced by these methods.

In the first method, a cold isostatic pressing (CIP)
After compression-molding into a near net shape, the amorphous alloy powder is sintered under heating under the above conditions to obtain a sintered body. Heating rate is 5 ° C when heating
The faster it is, the faster it is. Further, the heating time is preferably 5 minutes or more. Further, this heating is preferably performed in a vacuum furnace having a degree of vacuum of 10 ⁻³ Torr or less. During this heating, a viscous flow occurs due to its own weight or a small load, thereby increasing the density. As for the heating temperature and time, the relationship between the temperature when the amorphous alloy powder is heated and the crystallization time is determined in advance, and the conditions under which crystallization does not occur are determined from the result. For example, Co
_In the case of _79.5 Nb ₁₅ Zr _5.5 , the relationship between the temperature and the crystallization time is as shown in the graph of FIG. In the graph of FIG. 1, a portion below the solid line (A) is an amorphous region, and an upper portion is a crystalline region. The reason why the lower limit of the heating temperature is set to a temperature lower by 100 ° C. than the crystallization temperature is that if the temperature is higher than this temperature, viscous flow occurs and sintering and densification are performed. This lower limit temperature is
This is shown by a broken line (B) in the figure. The temperature may be kept constant until the heating is completed, or may not be constant within the above-mentioned temperature range.

Further, in the first method, the sintered body is subjected to the above conditions under the above conditions.
By performing HIP, the density of the sintered body can be further increased without promoting the crystallization of the amorphous alloy. The lower limit of the HIP execution temperature is set to a temperature lower by 100 ° C. than the crystallization temperature because if the temperature is higher than this temperature, viscous flow occurs and high density can be achieved. The temperature may be kept constant until the end of the HIP, or may not be constant within the above temperature range.

In the above-mentioned second method, when a molded article compressed and formed into a near-net shape is placed in a larger metal capsule and HIP is performed under the above conditions, sintering and densification of the amorphous alloy powder are performed. Can be done simultaneously. HI
When performing P, the inside of the capsule is preferably kept in a vacuum state having a degree of vacuum of 10 ⁻³ Torr or less. As the ceramic powder to be filled in the capsule together with the molded body, for example, alumina powder or glass powder containing alumina as a main component is used. The ceramic powder transmits the pressure during the HIP to the compact. When heating to the HIP molding temperature, the heating rate is preferably 5 ° C./min or more, and the faster the heating rate, the better. The molding temperature and time are obtained in advance by determining the relationship between the molding temperature and the crystallization time when the amorphous alloy powder is pressed,
From the results, conditions that do not cause crystallization are determined. For example, in the case of Co _79.5 Nb ₁₅ Zr _5.5 , the relationship between the molding temperature and the crystallization time is similar to the heating temperature and time before HIP in the first method. The lower limit of the HIP temperature is set to a temperature lower by 100 ° C. than the crystallization temperature because if the temperature is higher than this temperature, viscous flow occurs and sintering and densification can be performed simultaneously. The temperature may be kept constant until the molding is completed, or may not be constant within the above temperature range.

In addition, the two methods of the present invention include Ni-Ti, Ti-Al, Nb
It is also applicable to amorphous alloys such as -Sn, Bi-Sr-Ca-Cu. Among them, for example, in the case of Ni ₅₀ Ti ₅₀ , the relationship between the heating temperature or the forming temperature and the crystallization time is as shown in the graph of FIG. In the graph of FIG. 2, a portion below the solid line (A1) is an amorphous region, and an upper portion is a crystalline region. Further, the lower limit of the heating temperature or the molding temperature is shown by a broken line (B1) in FIG.

According to the method of the present invention, since an amorphous alloy powder produced by a mechanical alloying method or a mechanical grinding method is used, an oxide film does not exist on the surface of the amorphous alloy powder, and CIP and subsequent By the HIP, pressure can be isotropically applied to the amorphous alloy powder, so that a large-sized sintered body having a high density and a uniform density can be obtained. Further, according to the method of the present invention, after encapsulation in a rubber or plastic capsule and compression molding into a near net shape by CIP,
Since the sintering is performed, the capsule for CIP can be easily manufactured. As a result, the manufacturing cost of the sintered body is reduced and the sintered body is suitable for mass production. Further, according to the method of the present invention, crystallization of the amorphous alloy is prevented. Therefore, the sintered body manufactured by the method of the present invention has a higher density than the conventional one and is kept in an amorphous state, and has a high performance as a magnetic component such as a torque sensor of an electric power steering device. Can be manufactured. Furthermore, since the obtained sintered body has a high density, its strength is increased and it becomes possible to perform machining.

In particular, according to the second method, a near-net-shaped compact formed by CIP is encapsulated in a larger metal capsule together with a high-melting point, high-hardness ceramic powder as a secondary pressure medium and HIP. , Sintering and high density after CIP can be performed in one step, and the operation becomes easier. Moreover, as the capsule, a simple cylindrical one can be used regardless of the shape of the molded body, and the production thereof is simplified.

Examples Hereinafter, examples of the present invention will be described together with comparative examples.

Example 1 Co powder, Nb powder, and Zr powder were _mixed with Co _79.5 Nb ₁₅ Zr _5.5
And the resulting mixed powder was made amorphous by a mechanical alloying method or a mechanical grinding method using a media stirring type ball mill to produce an amorphous alloy powder having an average particle diameter of 20 μm. Then, the amorphous alloy powder, Ar gas atmosphere inside diameter 15mm in, encapsulated in a rubber capsule length 30 mm, diameter and compression molded by CIP at pressure of 40 kg / mm ² 10 m
m, a molded body with a length of 25 mm were produced. Then, the formed body is heated to 575 ° C. at a temperature rising rate of 20 ° C./min in a vacuum furnace having a degree of vacuum of 1 × 10 ⁻⁵ Torr.
Hold for 5 minutes and sinter. Thereafter, the sintered body is heated to 565 ° C. at a heating rate of 18 ° C./min, and maintained at this temperature,
HIP without encapsulation, time 30 minutes, A
compression molded under the conditions of r gas pressure 20 kg / mm ^2, a diameter of 8 mm, length 20
mm sintered body was manufactured.

When the density ratio of the sintered body manufactured in this manner was measured, it was 98%. When the sintered body was subjected to X-ray diffraction using a diffractometer, an amorphous state was maintained.

Example 2 Co powder, Nb powder, and Zr powder were mixed so as to have an atomic weight ratio of Co ₃₅ Nb ₁₁ Zr ₄ , and the obtained mixed powder was made amorphous in the same manner as in Example 1 above. Average particle size 20
A μm amorphous alloy powder was produced. Then, this amorphous alloy powder, the inner diameter of 12 mm in an Ar gas atmosphere,
It was sealed in a 40 mm long rubber capsule and compression molded by CIP at a water pressure of 20 kg / mm ² to form a molded body having a diameter of 10 mm and a length of 30 mm. Then, this molded body is 13 mm in inner diameter, length
Alumina powder was put into a 50 mm copper can together with the alumina powder, and the copper can was closed and encapsulated while degassing from the inside of the copper can.
The degree of vacuum inside the capsule was 1 × 10 ⁻⁵ Torr. Then, it is heated to 560 ° C. at a heating rate of 13 ° C./min, and is compression-molded by HIP under the conditions of an Ar gas pressure of 20 kg / mm ² for 1 hour while maintaining this temperature, and is 8 mm in diameter and 25 mm in length. A sintered body was manufactured.

The density ratio of the sintered body thus manufactured was measured and found to be 99%. Further, when this sintered body was subjected to X-ray diffraction using a diffractometer, it was partially crystallized, but most of the sintered body was kept in an amorphous state.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the crystallization time and the heating temperature or molding temperature of the Co _79.5 Nb ₁₅ Zr _5.5 amorphous alloy powder, and FIG. 2 is the crystallization temperature and the heating temperature or the molding temperature of the Ni ₅₀ Ti ₅₀ amorphous alloy powder. It is a graph which shows the relationship with time.

Continuation of the front page (72) Inventor Tsutomu Tane 3-5-8 Minamisenba, Chuo-ku, Osaka-shi, Osaka Inside Koyo Seiko Co., Ltd. (56) References JP-A-3-94031 (JP, A) JP-A-3 -267326 (JP, A) JP-A-62-74032 (JP, A) JP-A-4-341502 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22F 1/00- 7/08 C22C 1/04-1/05 C22C 33/02

Claims (2)

(57) [Claims] 1. An amorphous alloy powder produced by a mechanical alloying method or a mechanical gliding method is encapsulated in a rubber or plastic capsule, and compression molded into a near net shape by cold isostatic pressing. The body is heated for at least 100 ° C lower than the crystallization temperature and at a temperature in the range of not more than the crystallization temperature for a predetermined period of time. A method for producing a sintered body made of an amorphous alloy powder, which is compression-molded in a time period during which no crystallization takes place. 2. An amorphous alloy powder produced by a mechanical alloying method or a mechanical gliding method is encapsulated in a rubber or plastic capsule, and compression molded into a near net shape by cold isostatic pressing. The body is placed in a larger metal capsule and the gap is filled with a ceramic powder as a secondary pressure medium, and then below the crystallization temperature.
A method for producing a sintered body made of an amorphous alloy powder, wherein the amorphous alloy is compacted by hot isostatic pressing in a temperature range not lower than 100 ° C. and not higher than a crystallization temperature for a time during which the amorphous alloy does not crystallize.