JPH075938B2 - Method for producing rapidly solidified metal-based powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a rapidly solidified metal-based powder suitable for powder metallurgy.

[Prior Art] In recent years, a rapidly solidified powder for powder metallurgy with excellent characteristics has been developed. Conventionally, the rapidly solidified powder is produced by a metal substrate method, a water atomizing method, a gas atomizing method, or the like. Manufactured by the method. In these manufacturing methods, in principle, a molten liquid having a desired powder composition is caused to collide with a solid, a liquid, or a gas serving as a cooling medium, whereby the molten liquid is atomized and rapidly solidified, and then produced. The intended rapidly solidified powder is obtained by separating the powder and the cooling medium.

[Problems to be solved by the invention]

However, in the conventional powder manufacturing method as described above, it is essentially necessary to separate the produced powder and the cooling medium, which inevitably causes the following problems.

(A) In a manufacturing method using a solid substance substrate as a cooling medium, such as a metal substrate method, the produced powder often adheres to the cooling medium, which hinders the manufacturing work. Further, the obtained powder is in the form of flakes and has poor fluidity and cannot be used as a raw material for powder metallurgy unless re-pulverized, and if re-pulverized, contamination of impurities cannot be avoided, which is not preferable.

(B) In a production method using a liquid substance as a cooling medium, such as a water atomizing method, it is necessary to evaporate and dry the liquid in order to separate the produced powder and the liquid cooling medium, which consumes a lot of energy. . Further, due to the reaction with the liquid cooling medium, oxides, hydroxides, etc. are often generated on the surface of the obtained powder, and the sinterability decreases. Therefore, as it is, it is not suitable for powder metallurgy, and it is necessary to go through a reduction or degassing process, etc., and it is inevitable to raise the cost. Further, depending on the component composition, reduction is extremely difficult, or the rapidly solidified structure of the powder is impaired during the reduction and degassing steps, which is not preferable.

(C) In the production method using a gas substance as a cooling medium, such as a gas atomizing method, the obtained powder often contains a gas cooling medium, or when inexpensive air or nitrogen gas is used as the gas cooling medium, The resulting powder often forms oxides or nitrides on the surface thereof, and causes the same problems as when the above liquid substance is used as the cooling medium. Further, when an inert gas is used as the cooling medium, the obtained powder has a shape close to a true sphere, resulting in poor moldability. Furthermore, the cooling rate of the molten substance is slow, and a rapidly solidified powder having excellent properties cannot be obtained. In the gas atomizing method, some methods using powder as an auxiliary medium for cooling have been proposed (Japanese Patent Publication No. 49-6755 and Japanese Patent Publication No. 52-19539), but these are usually used as a main cooling medium. An inert gas is used in the same manner as the gas atomization of No. 1 and is not intended to improve the cooling rate.

[Means for solving problems]

Therefore, the present inventors have conducted research to solve the problems of the above-described conventional powder manufacturing technology, and as a result, many of the above problems are essentially to separate the cooling medium used for powder manufacturing from the powder. It was found that this is due to the fact that this is hindered by the adhesion and reaction between the powder and the cooling medium, which is necessary, and the powder manufacturing method that does not include this separation step solves the problems of the prior art. Therefore, it has been found that using a powder having the same composition as the molten substance as the cooling medium is an effective means for implementing this.

The present invention has been made based on such findings, in which a metal powder having an average particle diameter of 1 to 500 μm is introduced into a cylindrical container which rotates at a high speed at a peripheral speed of 20 m / sec or more, and the metal powder is centrifuged. It is rotated at a high speed together with the cylindrical container while being attached to the inner wall of the cylindrical container by force, toward the metal powder that is attached to the inner wall of the cylindrical container and is rotating at a high speed, and has substantially the same composition as the metal powder. The method is characterized by a method for producing a rapidly solidified metal-based powder in which molten metal is made to collide and the molten metal is rapidly solidified and simultaneously atomized.

The metal powder is preferably cooled to a sufficiently low temperature. Further, if the average particle size of the metal powder is 500 μm or more, flakes are contained in the produced powder, and the fluidity thereof is reduced, which is not preferable. On the contrary, if the average particle size of the metal powder is 1 μm or less, a large amount of powder having a particle size of 1 μm or less is contained in the obtained powder, which deteriorates the fluidity and the filling property, which is not preferable. Therefore, the average particle size of the metal powder is 1 to 500.
It is preferably in the range of μm.

In order for the metal powder to stick to the inner circumference of the cylinder, the centrifugal force applied to the metal powder needs to be sufficiently larger than the gravity. In other words, the centripetal acceleration in the inner circumference of the cylinder must be sufficiently larger than the gravitational acceleration G (9.8 m / sec ² ), but this condition is that the rotation speed is about 100 PPM if the inner diameter of the cylinder is 1 m. (5.6 G, peripheral speed: 5.2 m / sec), it is a condition that can be easily achieved, and in the range of peripheral speed: 20 m / sec or more, which will be described later, it is a condition that is always satisfied in a practically possible cylindrical inner diameter.

With respect to the peripheral speed of the inner circumference of the cylinder, the higher the peripheral speed, the smaller the particle size of the produced powder, and the cooling rate also increases accordingly. To obtain a 10 ⁴ ° C. / sec or more cooling rate of the object of the present invention, the peripheral speed is at least 20 m / sec or more, preferably more than necessary 40 m / sec.

The ratio X of the amount of the metal powder to the amount of the molten substance must be sufficiently large so that the molten substance is cooled and solidified sufficiently and rapidly, while the heating of the cooling powder is not excessive. That is, for the target substance, the following must be satisfied: latent heat of fusion + specific heat of liquid phase x (melting metal temperature-melting point) + specific heat of solid phase x (melting point-limit temperature) <X x specific heat of solid phase x (limit temperature-powder temperature for cooling) There is. Here, the critical temperature means that both temperatures become equal due to heat transfer from the molten metal to the metal powder (the temperature at that time is T ₀ ), and this heat causes the rapidly solidified structure of the cooling powder to Is an upper limit temperature of the temperature T ₀ that is not damaged during the cooling of the powder, and this temperature is different depending on the composition of the powder, but is about 200 to 500 ° C. for aluminum alloy powder, for example. When X is calculated from the above equation, it is found that the value is 1.5 or more, preferably 3 or more in a usual metal composition. The upper limit of X is about 20 and it is industrially meaningless to use a value higher than this. Therefore, the ratio of the amount of the metal powder to the molten metal: X is preferably 1.5 to 20.

When the molten metal is collided with the metal powder under the above conditions, the molten metal is finely divided, and is rapidly cooled and solidified by releasing heat to the metal powder for cooling, and remains adhered to the metal powder or separated from it. Will be collected together.

The metal powder may be a pure metal powder or an alloy powder, but after sufficiently cooling the recovered powder,
It is possible to produce a rapidly solidified metal base powder by repeating reuse of a part of the metal powder for cooling.

The powder manufacturing process according to the present invention can be carried out by a batch process, but at the same time as the powder manufacturing, the powder can be manufactured by partially making holes in the rotating cylindrical container or by making the bottom of the container into a needle-like shape. It is also possible to carry out continuous treatment by taking out a part and re-supplying it as a cooling metal powder.

〔Example〕

Next, the present invention will be specifically described based on Examples.

FIG. 1 is a schematic view of an apparatus for carrying out the method for producing a rapidly solidified metal-based powder according to the present invention. In the above FIG. 1, 1 is a cylindrical container, 2 is a motor, 3 is metal powder, 4 is an electric furnace, 5 is a crucible, 6 is an Ar gas cylinder for pressurizing the inside of the crucible, 7
Is a molten metal, 8 is a sliding nozzle having a slide 9, 10 is an elevating device, 11 is a rack attached to the outer periphery of a cylindrical container, 12 is a pinion, 13 is a mortar-like bottom, and 14 is a discharge port.

The bottom of the cylindrical container 1 is provided with a mortar-shaped bottom 13 having a discharge port 14, and the body of the cylindrical container has a rack.
11 is installed. The rack meshes with a pinion 12 attached to the shaft of the motor 2, and the rotation of the motor 2 causes the cylindrical container 1 to rotate.

The crucible 5 is kept warm in the electric furnace 4, and the crucible 5 can be raised and lowered by an elevating device 10. Furthermore, the crucible 5 is connected to a crucible pressurizing cylinder 6 so as to pressurize the crucible molten metal 7.

Using such an apparatus, a rapidly solidified metal base powder was produced as follows.

A stainless steel cylindrical container 1 having an inner diameter of 400 mm is rotated at a rotation speed of 3000 rpm by a motor 2 (peripheral speed: 63 m / sec,
2 × 10 ³ G), 2 kg of pure aluminum powder having a particle size of −100 to +350 mesh and an average particle size of 50 μm, which was previously produced by the gas atomizing method, was attached to the inner surface of the cylindrical container 1 by centrifugal force.

On the other hand, a pure aluminum ingot is charged into the crucible 5,
It is heated and melted to a temperature of 750 ° C. by the electric furnace 4 and kept at that temperature. The surface of the molten aluminum 7 is pressurized by Ar gas pressure from the Ar gas cylinder 6, and the slider 9 of the sliding nozzle 8 having an inner diameter of 1 mm provided at the bottom of the crucible is slid to slide the molten pure material from the sliding nozzle 8. Aluminum at a flow rate of 1 kg / min for 30 seconds
0.5 kg was forcibly discharged and collided with pure aluminum powder 3 attached to the inner surface of the cylindrical container 1 by centrifugal force. It is preferable that the sliding nozzle 8 is attached so as to be inclined with respect to the side wall of the cylindrical container, and the molten metal 7 is caused to collide obliquely with the metal powder 3 adhered thereto by centrifugal force.

Further, it is preferable that the crucible 5 is moved up and down by the elevating device 10 and the molten metal 7 is adjusted and controlled so as to uniformly collide with the entire surface of the metal powder 3.

Since the metal powder 3 also has the function of rapidly solidifying the molten metal 7 that has collided, it is desirable that the temperature be as low as possible, but room temperature is practically sufficient.

In this way, after the molten metal 7 is uniformly impinged on the entire surface of the metal powder 3 adhered by the centrifugal force, when the rotation of the motor 2 is stopped, the metal powder adhered by the centrifugal force and the rapidly solidified fine particles are collided by the collision. The powdered powder falls together and is collected in the center by the mortar-shaped bottom 13 and the discharge port
Emitted from 14. A part of the rapidly solidified metal base powder discharged from the discharge port 14 may be cooled, introduced into the cylindrical container 1 and reused as the metal powder 3.

The obtained rapidly solidified metal-based powder was mixed with a powder in which molten aluminum was adhered and solidified on the surface, that is, a powder having a cross section as seen in the optical micrograph of FIG. The cooling rate estimated from the size of the dendrite structure of the solidified aluminum seen in the above optical micrograph was about 10 ⁵ ° C / sec. The average particle size of the entire rapidly solidified metal-based powder obtained was 60 μm, and the oxygen content was 0.03.
It was in%.

〔The invention's effect〕

According to the production method of the present invention, it is not necessary to separate the generated powder and the cooling medium after atomizing-quenching and solidifying the molten metal, and the powder obtained by the present invention has the molten metal on the powder. The shape is irregular because it is adhered and solidified.

Therefore, the moldability, the fluidity, and the filling property are good, the impurities are few and the structure is fine, and it is possible to provide an excellent powder as a raw material powder for powder metallurgy.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for carrying out the present invention, and FIG. 2 is an optical micrograph of a cross section of a rapidly solidified metal-based powder produced by the production method of the present invention. 1 ... Cylindrical container, 2 ... Motor, 3 ... Metal powder, 4 ... Electric furnace, 5 ... Crucible, 6 ... Ar gas cylinder, 7 ... Molten metal, 8 ... Sliding nozzle, 9 ... Slider, 10 ...... Lifting device, 11 ...... Rack, 12 ...... Pinion, 13 ...... Bowl bottom, 14 ...... Discharge port.

Claims (6)

[Claims] 1. A metal powder is introduced into a high-speed rotating cylindrical container, and the metal powder is rotated at a high speed together with the cylindrical container while being attached to the inner wall of the cylindrical container by centrifugal force. Toward the above-mentioned metal powder, the molten metal having substantially the same composition as the above-mentioned metal powder is made to collide, and the above-mentioned molten metal is rapidly solidified, and at the same time, atomized and solidified. Law. 2. The average particle size of the metal powder is 1 to 500 μm.
The method for producing a rapidly solidified metal base powder according to claim 1, wherein 3. The rapid solidification method according to claim 1, wherein the total amount of the metal powder introduced into the high-speed rotating cylindrical container is 1.5 to 20 times the total amount of the molten metal. Manufacturing method of metal-based powder. 4. The high-speed rotation speed of the cylindrical container is 20 m / sec.
The method for producing a rapidly solidified metal-based powder according to any one of claims 1 to 3, wherein the peripheral speed is the above. 5. The method for producing a rapidly solidified metal-based powder according to claim 1, wherein the rapidly solidified metal-based powder is reused as the metal powder. 6. The method for producing a rapidly solidified metal-based powder according to claim 1, wherein the metal powder is a pure metal or alloy powder.