JPH0598311A - Sintered composite and its production - Google Patents

Abstract

PURPOSE:To produce a sintered composite having a uniform component distribution from plural kinds of materials by coating the nucleus grain with a conductive matreial to form a capsule powder and impressing a pulse voltage on the powder while pressing the powder in a die. CONSTITUTION:A conductive coating grain 3 (lead, tin, etc.) and a nucleus grain 2 (porous silicon nitride, etc.) are mixed in a specified ratio, the mixture is placed in a electrifying device, sufficiently agitated and electrified, and the coating grain 3 is electrostatically stuck to the surface of the nucleus grain 2. At this time, the diameter of the coating grain 3 is controlled to about 1/10 of that of the nucleus grain 2. The grains 2 and 3 stuck electrostatically to each other are placed in a housing provided with an impeller, and the coating grain 3 is mechanically and firmly attached to the surface of the nucleus grain 2 by the centrifugal impact force to obtain a capsule powder 1. The powder 1 is placed in a sintering die, a pulse voltage is impressed while pressing the powder to generate an electric discharge between the coating grains 2, and the grains are joined to form a sintered composite.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered composite body formed by sintering powders made of different materials and a method for producing the same.

[0002]

2. Description of the Related Art A technique for forming a sintered body by heating metal powder or non-metal powder has been practiced for a long time. In addition, heat resistance, wear resistance, and
Sintered composites with improved rigidity and sliding properties are also used in various fields.

For example, aluminum powder and aluminum alloy powder, copper powder and copper alloy powder, etc. are formed as a sintered composite and used as a sliding member such as a bearing, but it is not possible to uniformly mix the powders. Very difficult and very difficult to form a uniform material. When iron-based metal powder is sintered and used as a sliding member such as a bearing, by mixing powder of a soft material such as lead or tin, the conformability of the sliding surface is improved and sliding characteristics are improved. However, it is difficult to uniformly disperse lead and tin, and the melting point of lead and tin is lower than that of iron.
Since the temperature difference is large, an iron-based sintering temperature of, for example, 100
When sintered at 0 ° C., there is a problem that low melting point metals such as lead and tin are completely melted and flow downward.

[0004]

By the way, although a metal material having a resilience like a rubber ball has been developed, a metal material having a viscoelastic property like rubber at room temperature is not found. If a metal material with such properties can be developed,
The material and existing metal materials can be soldered or spot-welded to have a wide range of applications, and the advent of such materials is desired.

If a composite material composed of a synthetic resin and a metal can be molded by sintering, it becomes a material that is lightweight, has high rigidity, is easy to mold and has good machinability, and the advent of such a material is desired. ..

An object of the present invention is to provide a sintered composite body having a uniform component distribution in a sintered body made of plural kinds of materials. Another object of the present invention is to provide a sintered composite body having a uniform component distribution even if a plurality of types of materials having different melting points are used. Still another object of the present invention is to provide a manufacturing method capable of easily manufacturing the above sintered composite body.

[0007]

According to the present invention, in a method for producing a sintered composite body composed of a plurality of kinds of materials, the surface of core particles is coated with a conductive coating material to form capsule powder. A method for producing a sintered composite body, which comprises the steps of: filling a capsule die with the capsule powder; and applying a pulsed voltage to the capsule powder filled in the die to obtain a sintered body. Provided.

Further, there is provided a sintered composite body comprising a capsule powder in which the surface of the core particle is coated with a coating material having a melting point higher than that of the core particle and having conductivity, and the capsule powder is solidified.

[0009]

[Function] As a core particle, a powder composed of a low melting point material, a rubber material, a synthetic resin powder, and a metal is coated with a conductive material to form a capsule powder, and the capsule powder is housed in a sintering mold. A pulse voltage is applied while applying pressure to generate discharge between the coating materials, and these are combined to form a sintered composite.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings. In the present invention, an example in which fine particles as a coating material is attached to the periphery of core particles constituting a capsule powder as a composite powder, and one in which the entire periphery of the core particles is coated with a coating material is used. An example can be given, but first, an explanation will be given of an example in which a coating material composed of fine particles is applied around the core particle, and then an example of using a capsule powder in which the entire periphery of the core particle is coated with the coating material. Will be explained.

FIG. 1 is a model view showing a capsule powder used in the sintered composite body according to the present invention, and FIG. 2 is a model view of the aggregate.

In FIG. 1, reference numeral 1 is a capsule powder which is a sintered composite and comprises a core particle 2 and a plurality of coated particles 3 coated on the surface of the core particle 2. The core particle 2 may be a metal or a non-metal as in each of the examples described later, and any material may be used. The coated particles 3 are made of a conductive material. A method of depositing the coating particles 3 on the surface of the core particles 2 will be described. First, the core particles 2 and the coating particles 3 are mixed at a predetermined ratio, and this mixture is put in a charging device and well stirred to perform a charging treatment. Then, the coating particles 3 are attached to the surfaces of the core particles 2 by electrostatic force. The diameter of the coated particles 3 is preferably about 1/10 of that of the core particles 2. The adhesive force due to this electrostatic force is extremely weak, and the strong shaking causes the core particles 2 and the coated particles 3 to separate. Therefore, the core particles 2 and the coated particles 3 attached to each other by these electrostatic forces are housed in a housing equipped with a rotor, and the powder of the coated particles 3 is mechanically bonded to the surface of the core particles 2 by a centrifugal impact force. Firmly adhere.

The state in which the coating particles 3 are fixed on the surface of the core particles 2 by the above method (hereinafter referred to as the hybridization method) differs depending on the properties of the core particles 2 and the coating particles 3, mainly the hardness. For example, (a) When the coated particles 3 are harder, the coated particles 3 are fixed in a state of being embedded in the surface of the core particles 2. (B) When the coated particles 3 are softer, the coated particles 3 are adhered and fixed on the surface of the core particles 2 in a crushed state. Regarding the method for producing such capsule powder, for example, Japanese Patent Application Publication: 62-250942.
It is disclosed in the publication.

Here, the capsule powder constituted by the above method will be examined from the following three viewpoints while comparing with the capsule powder constituted by other methods. 1) Are there voids between the coated particles 3 immobilized on the surface of the core particles 2? 2) Can air enter into the void between the core particle 2 and the coated particle 3? 3) Is there a metallurgical bond at the interface between the core particle 2 and the coated particle 3?

FIG. 3 shows the result of the above examination. As can be seen from FIG. 3, the capsule powder formed by the hybridization method has a characteristic of “yes” in response to the questions in the above items 1) and 2).

In the present invention, it is also possible to use a capsule powder in which a coating material is applied to the surface of the core particles by a displacement plating method, an electroless plating method, a sputtering method or the like.

Next, a composite body (sintered body) which is formed by filling the above-mentioned capsule powder in a mold and applying a pulsed current will be described.

FIG. 2 is a model view of an aggregate formed by sintering capsule powder. In FIG. 2, reference numeral 4 denotes an aggregate in which the above-mentioned capsule powders are sintered and bonded, and the core particles 2 whose surfaces are covered with the coating particles 3 are integrated by bonding between the coating particles on the surface. is there.

FIG. 4 is a block diagram of a sintering apparatus for producing a composite body by such sintering. Reference numeral 10 shown in the figure is a sintering type, the main body of which is made of high strength tungsten steel or the like. And the powder 1 to be sintered is in the center.
A hole for accommodating a is formed, and the insulating layer 11 is formed on the inner peripheral wall of the hole.
Is provided. Reference numeral 12 is an upper pin, and 13 is a lower pin, which are respectively inserted into the holes at the center of the sintering die 10, and a powder of the material to be sintered is filled between these two pins to obtain a sintered body. Is processed into. Reference numerals 14 and 15 denote electrodes, and pressure is applied in the direction of the arrow by a hydraulic mechanism (not shown) to press the powder contained in the sintering mold through the upper pin 12 and the lower pin 13, and to apply a voltage to the powder. Is applied. Then, the switches SW1,
A series circuit of SW2 and a capacitor C is connected, and high voltage power from the variable power source 16 is charged in the capacitor C via the resistor R and the closed circuit switch SW2, and when the switch SW1 is closed in this state. , Electrodes 14, 1
A sharp pulsed high voltage is applied to the pressurized powder through 5 and the upper and lower pins 12 and 13 to generate an electric discharge, and the oxidation applied to the surface of the coating material of the capsule powder by repeating the application of the pulsed voltage. Objects and the like are destroyed, the surface of the coating material is purified, and the coating materials fuse together. In addition,
Reference numeral 17 shown in the figure is a control mechanism for controlling the opening and closing of the switches SW1 and SW2.

The above-mentioned sintering action will be described in more detail. In the above sintering process, since a current flows through the capsule powder, the coating material must naturally be conductive. At this time, only the surface of the coating material is instantaneously melted by the application of the pulse voltage, and the capsule powders are bonded to each other. At this time, many gases are present in the voids between the capsule powders filled in the mold. This gas escapes from the mold when the capsule powder is compressed or a pulse current flows.
Further, the temperature of the capsule powder itself rises due to the flow of the pulse current, and the temperature of the capsule powder rises due to a decrease in impedance due to the fact that the density of the capsule powder starts to increase. The material of the core particles of the capsule powder, for example, a material such as synthetic resin or rubber that generates gas from the inside when heated, ejects gas from the core particles during sintering, but in the capsule powder formed by the hybridization method, The gas passes through the voids existing in the coating material surrounding the core particles. Therefore, the composite can be formed by sintering without changing the shape of the capsule powder due to the ejection of gas and without impairing the adhesion between the core particles and the coating material.

Next, a first specific example of the sintered composite body of the present invention will be described. As the core particle 2, a porous core particle obtained by pulverizing porous silicon nitride is used, and the core particle 2 is formed on the surface of the core particle 2.
A sintering die 10 in which a lead or tin coating material having a smaller particle size is applied by a hybridization method to produce capsule powder, and a predetermined amount of this capsule powder 1a is inserted into the lower pin 13 of the sintering apparatus shown in FIG. Fill the hole of the upper pin 1
It is pressed with a predetermined pressure by 2. Then, the control mechanism 17 controls the opening and closing of the switches SW1 and SW2,
A pulse voltage is applied to the capsule powder 1a via the electrodes 14 and 15 and the upper and lower pins 12 and 13. For this reason, an electric discharge occurs between lead or tin, which is the coating material forming the capsule powder 1a, and the lead or tin powder, which is the coating particle, is fused by purification of the surface of the coating material and heat generation due to repetition of this discharge. Be combined. During this fusing operation, the capsule powder is heated and the gas contained therein expands, but since there are innumerable gaps in the coating material, the gas is ejected from the gap to the outside of the capsule powder, In addition, it escapes from the mold through the gaps between the capsule powders. Therefore, the core particles made of porous silicon nitride and the coating material are not separated from each other, and a sintered body as an aggregate of capsule powder is formed as shown in FIG.

As described above, as the first specific example, an example in which porous silicon nitride is used for the core particles 1 and lead or tin is used for the coating material 3 has been described. As a modification, copper or aluminum is used as the coating material 3. It is also possible to use a powder and to use other porous ceramics such as porous alumina for the core particles.

In the above specific example, the core particles of the capsule powder are formed by crushing porous silicon nitride. Therefore, the surface of the core particle is extremely uneven. For such nuclear particles, the coating material may not be attached to the surface of the nuclear particles by the hybridization method, but the coating material may be attached to the surface of the nuclear particles by the sputtering method. That is, even if the coating material is deposited by sputtering, some gaps or cracks will occur in the coating material due to the unevenness of the core particles.

Next, a second specific example of the sintered composite body of the present invention will be described. A low melting point metal lead or tin powder is used as the core particle 2, and an iron powder having a particle size smaller than that of the core particle 2 is adhered to the surface by a hybridization method to form a lead or tin core capsule powder. A predetermined amount of the capsule powder 1a is filled in the hole of the sintering die 10 into which the lower pin 13 of the sintering apparatus shown in FIG. 4 is inserted, and pressed by the upper pin 12 at a predetermined pressure.

Then, the control mechanism 17 switches SW
1, SW2 is controlled to be opened and closed, and a pulse voltage is applied to the capsule powder 1a via the electrodes 14 and 15 and the upper and lower pins 12 and 13.

Therefore, an electric discharge is generated between the iron powders which are the coated particles constituting the capsule powder 1a, and the iron powders which are the coated particles are melted by the heat generation and the purification of the surface of the iron powder due to the repetition of this discharge. Wear and bond. The lead or tin powder is coated with the iron powder by such fusion of the coating material on the surface, and is sintered as an aggregate of the capsule powder as shown in FIG.

As described above, as the second specific example, the core particles 1 are made of lead or tin powder and the coating material 3 is made of iron powder. As a modification, copper or aluminum powder is used as the coating material 3. Also, it is possible to use other metals for the core particles by appropriately selecting the sintering conditions. Therefore, this type of sintered body can be used as a sliding member such as a bearing or a member having improved heat resistance of aluminum.

As described above, according to the second embodiment, the capsule powder in which the surface of the core particle is coated with the conductive coating material is sintered by applying a pulse voltage in the molding, and the composite powder is sintered. Since the body is composed, it is possible to obtain a sintered composite with a uniform component distribution, and the surfaces of the coating materials are cleaned and heated to bond the coating materials to each other, so that they can be bonded without affecting the core particles. Therefore, it is possible to obtain a sintered body made of a plurality of materials having a large difference in melting point, which is impossible as a sintered body. In particular, it is possible to obtain a sintered composite of capsule powders using a low melting point material for the core particles and a high melting point material for the covering element.

Further, according to the second specific example, since the particle powder is used as the coating material for coating the core particles, the gas generated by heating during sintering can be degassed, and bubbles in the sintered body can be removed. Can be prevented.

Next, a third specific example of the sintered composite body of the present invention will be described. In this specific example, a non-metal, non-conductive material is used for the core particles forming the capsule powder.

In the third specific example, the core particles 2 have a particle size of 20 to 20.
Rubber particles of 500 μ are used, and as the coating material 3, for example, powder of conductive metal such as copper is used.

In this case, as the rubber particles of the core particles 2, for example, raw rubber is mixed with about 6% of sulfur, and vulcanized soft rubber having a particle size of 20 to 500 .mu. As the powder, about 30% of the particle size of soft rubber is used by volume and mixed, and capsule powder in which copper powder is adhered to the surface of the rubber particle by electrostatic attraction is prepared. ..

Then, in order to enhance the adhesion of the capsule powder to the copper powder, the capsule powder was housed in a housing equipped with a rotary blade of 2000 to 7000 rpm and centrifugally rolled to firmly adhere the copper powder to the surface of the rubber particles. Let

The capsule powder of rubber particles thus treated by the hybridization method was filled in the mold 10 of the sintering machine shown in FIG. 4 according to the first embodiment, and pulsed while applying a predetermined pressure. When a voltage is applied to generate a discharge between the copper powders of the coating material and sinter them, the core particles inside are not affected by heat and do not deteriorate, and only the copper on the surface rises in temperature. A diffusion-bonded sintered composite body can be obtained.

The combination of the core particles and the coating material in the third specific example is (rubber / copper), but the internal temperature of the core particles does not rise so much during sintering. As the material for the particles, ebonite with an increased sulfur content, natural rubber, styrene rubber, nitrile rubber, fluororubber, polyamide resin, low melting point metal such as tin, and the like can be freely selected. Further, as the metal material as the coating material, a conductive metal such as tin, lead, aluminum, iron, nickel and chromium can be freely selected.

Therefore, the elastic modulus of the composite sintered body can be freely changed by changing the core particles and the coating material.
Further, since the coating material is a metal, it is possible to perform soldering, spot welding, and the like, and it is possible to freely change the surface color tone and modification by plating. Note that, subsequently, specific examples of other combinations including some of the above-mentioned materials will be further described below.

Next, a fourth specific example of the sintered composite body of the present invention will be described. In the fourth specific example, a synthetic resin powder is used as the core particles 2 and is coated with a conductive metal powder. The synthetic resin material is used for a sintered body such as polycarbonate, polypropylene, polyethylene, or polyacetate. Can be selected by.

The synthetic resin powder has a particle size of 10 to 200.
μ, and a metal powder of copper, aluminum, or the like having a particle size of about 1/10 of this particle size is mixed, and adhered to the surface by electrostatic attraction as in the third specific example, and then centrifugally transferred. The surface is either moved or adhered by a spray method and is tumbled to firmly coat the surface, and a capsule powder having a synthetic resin material as a core is prepared by a hybridization method.

Then, according to the second or third specific example, the capsule powder is subjected to electric current sintering with a pulse current by a sintering apparatus. In this electric current sintering, since no current flows through the core particles, the temperature of the core particles does not rise, and the metal on the surface generates heat to obtain a sintered composite body in which diffusion bonding is performed.

Since the surface of the thus-produced sintered composite body is coated with a metal, it exhibits cutting properties similar to those of a metal, and can be cut like a metal.

Next, a fifth specific example will be described. In the fifth specific example, a spherical lead powder is used as the core particle 2, and a metal having a melting point higher than that of the core particle material such as silver is used as the coating material 3, which is formed by the sputtering method or the electroless plating method. The entire surface of the core particles is densely coated to form a capsule powder.

Next, according to the second or third specific example, the capsule powder is energized and sintered by a pulse current in a sintering machine. In this electric current sintering, since no current flows through the core particles, the temperature of the core particles does not rise, and the metal on the surface generates heat to obtain a sintered composite body in which diffusion bonding is performed. In addition, even if the sintering time becomes longer and the core particles of the capsule powder are heated, no gas is emitted from this, so the coating material does not separate from the core particles, and the strength of the formed sintered body is improved. Is not impaired.

Next, a sixth specific example will be described. In the sixth specific example, tin powder is used as the core particles 2, and this is coated with a conductive metal powder made of aluminum and used as capsule powder.

Then, tin powder and a metal powder such as aluminum having a diameter of about 1/10 of the diameter of the tin powder are mixed and adhered to the surface by electrostatic attraction as in the third embodiment. After that, it is centrifugally tumbled, or it is attached by a spray method and coated firmly on the surface by tumbling to prepare a capsule powder having tin as a nucleus by a hybridization method.

Next, the capsule powder is energized and sintered by a pulse current by a sintering apparatus according to the second or third embodiment. As the conditions for electric current sintering, the pressure applied to the capsule powder is 2000 kg and the pressing time is 99 seconds.
A pulse voltage was applied during this period. An enlarged cross-sectional photograph of the sintered composite thus obtained is shown in FIG.

Next, the seventh specific example will be described. In the seventh specific example, tin powder is used as the core particles 2, and a powder obtained by coating this with a conductive metal powder made of copper is used as a capsule powder.

Then, a tin powder and a metal powder made of copper having a diameter of about 1/10 of the diameter of the tin powder are mixed,
After being attached to the surface by electrostatic attraction as in the third specific example, it is centrifugally tumbled or is applied by a spray method and coated firmly on the surface by rolling, and tin is used as a core. The prepared capsule powder is prepared by the hybridization method.

Next, the capsule powder is energized and sintered by a pulse current by a sintering apparatus according to the second or third embodiment. As the conditions for electric current sintering, the pressure applied to the capsule powder is 2000 kg and the pressing time is 99 seconds.
A pulse voltage was applied during this period. An enlarged cross-sectional photograph of the sintered composite body thus obtained is shown in FIG.

Next, the eighth specific example will be described. In the eighth example, a polyamide resin (nylon resin) powder is used as the core particles 2, and a powder obtained by coating this with a conductive metal powder made of copper is used as a capsule powder.

Then, the polyamide resin powder and a metal powder made of copper having a diameter of about one tenth of the diameter of the polyamide resin powder are mixed, and the mixture is applied to the surface by electrostatic attraction as in the third embodiment. After adhering, it is centrifugally tumbled, or it is adhered by a spray method and coated firmly on the surface by tumbling to prepare a capsule powder having a polyamide resin as a core by a hybridization method.

Next, according to the second or third specific example, the capsule powder is subjected to electric current sintering with a pulse current by a sintering apparatus. As the conditions for electric current sintering, first, the pressure applied to the capsule powder was 2000 kg, and the pressing time was 1 minute. The pulse voltage was applied during the initial 30 seconds of this period. An enlarged cross-sectional photograph of the sintered composite body thus obtained is shown in FIG.

[0052]

As described above, according to the present invention, a discharge is generated between coating materials by pulsed current, and a film made of impurities such as oxides adhering to the surface of the coating material is surface-purified and coated. The surfaces of the materials are fusion bonded. Therefore, the internal core particles remain at a low temperature, and only the surface layer of the coating material rises in temperature to be in a state of joining, so that the core particles can be solidified without any influence. Then, as in the case of conventional DC current sintering, current flows only at the place where the coupling impedance between many powders is low, and it cannot be solidified, or even if solidified, it takes a long time for sintering. In contrast to the one requiring, the sintering by pulsed current requires a very short time until solidification. Therefore, even if the material forming the core particles has a low melting point, the core particles can be solidified without melting.

Further, in the case where the coating material is adhered to the surface of the core particles by the hybridization method, since the coating material is mechanically bonded to the core particles, a gap is formed between the coating materials, and baking is performed. Since the gas generated from the inside of the core particles at the time of binding smoothly escapes from this gap, the gas does not remain in the sintered composite. Further, since the gas escapes from between the coating materials, the coating material is not separated from the core particles, and the gas can be released without impairing the adhesion between the coating material and the core particles.

Furthermore, since a pulse current flows through the coating material during sintering, current control during sintering is easy.

In addition to the above, the present invention provides a sintered body formed by a pulsed current sintering method, in which a coating material having a melting point higher than that of the material forming the core particles is composed of capsule powder arranged around the core particles. In addition to the above, it is possible to provide a conductive sintered composite even when the core particles are non-conductive. Further, a sintered composite material in which no gas remains in the sintered body can be provided, and a sintered composite material having a strong bond between core particles can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a model diagram showing a composite powder body used in a sintered composite body according to the present invention.

FIG. 2 is a model diagram of an aggregate.

FIG. 3 is a characteristic comparison diagram of capsule powders.

FIG. 4 is a block diagram of a sintering device for firing a sintered composite body.

FIG. 5 is a photograph showing a cross section of a sixth example.

FIG. 6 is a photograph showing a cross section of a seventh example.

FIG. 7 is a photograph showing a cross section of an eighth example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Capsule powder 2 ... Nuclear element 3 ... Coating material 4 ... Assembly 10 ... Sintering type 11 ... Insulating layer 12 ... Upper pin 13 ... Lower pin 14 ... Electrode 15 ..Electrode 16 ... Variable power source 17 ... Control mechanism

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[Procedure amendment]

[Submission date] October 15, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

FIG. 5 is a photograph showing an enlarged cross section of a particle structure of a sixth specific example.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

FIG. 6 is a photograph showing an enlarged cross section of a particle structure of a seventh example.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] Figure 7

[Correction method] Change

[Correction content]

FIG. 7 is a photograph showing an enlarged cross section of a particle structure of an eighth example.

Claims (8)

[Claims] 1. A step of coating a core material with a coating material having conductivity to form a capsule powder, and a step of applying a pulse current in a mold for sintering the capsule powder to obtain a sintered body. A method for producing a sintered composite body, comprising: 2. The method for producing a sintered composite body according to claim 1, wherein the core particles have a melting point lower than that of the coating material. 3. The method for producing a sintered composite body according to claim 1, wherein the coating material comprises particles, and the particles are coated on the core particles by mechanical bonding. 4. The method for producing a sintered composite body according to claim 1, wherein the core particles are a non-conductive material. 5. A sintered composite body obtained by solidifying a capsule powder obtained by coating a coating material with core particles having a melting point lower than that of the coating material. 6. The sintered composite body according to claim 5, wherein the coating material has conductivity. 7. The sintered body according to claim 5, wherein the coating material is particles. 8. The sintered body according to claim 5, wherein the core particles are made of a non-conductive material.