JPH062010A - Method for sintering powder compact - Google Patents

Abstract

PURPOSE:To avoid the reaction of a conductive powder with a compact and the adhesion of powder to the compact at the time of sintering the compact consisting of a sinterable powder in the conductive powder by forming a coating film of a material non-reactive with the compact on the compact surface. CONSTITUTION:A coating film 14 consisting of a material, which does not react with a compact, is formed on the surface of the powder compact 13. The compact 13 is embedded in a conductive powder 12 as the pressure medium filled in a sintering die 11 consisting of an insulating material. The powder 12 is then pressed, a voltage is simultaneously impressed on the powder 12 to generate heat, and the compact 13 is sintered. In this case, since the coating film 14 does not react with the compact 13, the coating film is removed after sintering, and the sintered compact without the powder 12 being deposited on the surface is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method of embedding a powder compact preformed with a sinterable powder of metal, ceramics or the like in a conductive powder filled in a sintering die to obtain the conductive powder. The present invention relates to a sintering method in which a voltage is applied to the conductive powder to generate heat, and the powder compact is sintered while being pressed.

[0002]

2. Description of the Related Art As a sintering method for sintering a powder compact made of sinterable powder by using conductive powder, there is a method using an apparatus as shown in FIG. This device was published in 1989 by The Minerals, Metals & Materials societ.
y ", pages 387-396.

According to this method, a powder molding 3 made of carbide or metal is embedded in a granular conductive powder 2 filled in a sintering die 1 made of graphite, and the sintering die 1 is made to have a conductive plunger 4.
In this method, an electric current is passed in the axial direction while causing the conductive powder 2 to generate heat, and the powder compact 3 is sintered by the heat. In the above method, the conductive powder 2 has a high elastic modulus, a high fracture strength, and almost no binding property of the particles themselves, for example, carbon-9400, which is spherical graphite carbon.
(The brand name of Superior Graphite) is used. Further, during the pressurizing operation, an inert gas 5 such as nitrogen is caused to flow into the sintering die 1 in order to prevent the powder compact 3 and the conductive powder 2 as the pressure medium from being oxidized.

It has been reported that a silicon carbide powder compact and a neodymium-iron-boron powder compact were sintered by such a method. When a silicon carbide powder compact was used, a sintered compact with a relative density of 95.0% was obtained by applying a pressure of 4000 psi, applying a pressure of 13 psi and 1720 A for 4 minutes in a sintering mold having an inner diameter of 2 inches.

[0005]

A high-density sintered body can be obtained by the above method, but the powder compact 3 is formed because the powder compact 3 and the conductive powder 2 as a pressure medium are in contact with each other. Depending on the combination of the powder material and the material of the conductive powder 2, there has been a problem that the two react with each other to generate a carbide, and sometimes they are melted by a eutectic reaction.

In particular, in the case of a powder compact having a complicated shape having irregularities, if the conductive powder that has entered the recess of the compact reacts with the powder forming the compact and adheres to the surface of the compact, It is virtually impossible to remove the conductive powder after sintering. The present invention has been made in view of the above circumstances, and an object thereof is to provide a powder in which conductive powder does not react with a powder compact or sinter and adhere to the powder compact. It is to provide a method for sintering a molded body.

[0007]

The method for sintering a powder compact according to the present invention comprises forming a coating film made of a material that does not react with the powder compact on the surface of the powder compact, which comprises sinterable powder. A compact having a coating is embedded in a conductive powder filled in a sintering die, the conductive powder is pressed, and a voltage is applied to the conductive powder to generate heat to sinter the compact. .

[0008]

The conductive powder is heated by being electrically pressurized, and the Joule heat sinters the powder compact. At this time, the film formed on the surface of the powder compact is
Prevents the conductive powder from directly contacting the surface of the powder compact. On the other hand, since the coating does not react with the powder forming the powder compact, the coating does not adhere to the surface of the powder compact to the extent that it cannot be removed by electric current sintering.

Therefore, after the sintering, the sintered powder compact is taken out of the conductive powder and the coating film on the surface of the powder compact is removed, whereby the powder compact without the conductive powder adhered to the surface is sintered. Goods are obtained.

[0010]

Examples Examples of the sinterable powder used in the powder compact of the present invention include iron-based alloys such as stainless steel and tool steel, aluminum and its alloys, titanium and its alloys, and high melting point metals such as molybdenum. Etc. Sinterable metal powders; Electrically conductive and electrically insulating ceramics powders; Cemented carbide, cermet and other ceramics-based composite material powders;
And particle-dispersed or whisker-dispersed composite material powders. These powders are molded by injection molding, cold molding or the like to form a powder compact. When sintering the powder compact, a film is formed on the surface of the compact.

The coating is made of a material that does not react with the powder former. The constituent material of the coating is preferably one that does not react with the powder compact, and it is preferably electrically insulating so that no current flows to the powder compact during electric heating. Further, from the viewpoint of taking out the powder molded product after sintering, removing the coating film, etc., a material which does not react with the conductive powder and has releasability from the powder molded product is preferable. As a material satisfying such requirements, for example, boron nitride or a mixture of boron nitride and other oxide-based ceramics is preferably used.

The method for forming a film is not particularly limited as long as it is a method capable of forming a film with the above materials, but a spray method, a dip method, etc. are simple and economical. Although the thickness of the coating depends on the method of forming the coating, it is generally about 0.1 to 0.3 mm. The powder compact having the above coating is embedded in the conductive powder filled in the sintering die of the electric sintering machine. As the conductive powder, those having a high elastic modulus and a high strength and having no binding property in the particles themselves are preferably used.

The sintering method is the same as the conventional method for sintering powder compacts, but is a uniaxial pressing method in which the sintering die is pressed by a punch, and the pressing direction and the energizing direction are the same direction. Is common. FIG. 1 shows an embodiment of a uniaxial pressure type electric sintering apparatus for carrying out the sintering method of the present invention.

In FIG. 1, 11 is a sintering die made of an insulating material, and inside the sintering die 11 is a conductive powder 12 which is a pressure medium.
And a powder compact 13 is embedded in the conductive powder 12. A coating 14 is formed on the surface of the powder compact 13. An upper electrode 15 is provided above and below the sintering die 11.
And a lower electrode 16 are provided. The lower electrode 16 is fixed to a mount 18 on a press base 19 via a heat insulator 17, and the upper electrode 14 is attached to a punch 2 via a heat insulator 21.
2, the punch 22 is connected to the hydraulic ram 25 via the insulator 24 by the pressing ring 23.

Further, the light of an optical temperature measuring sensor 32, which can measure the temperature inside the sintering die without contact, passes through the peripheral surface of the support ring 26 supporting the periphery of the sintering die 11. A translucent window 28 has been opened. The portion of the sintered mold 11 corresponding to the light transmitting window 28 is made of a substance having excellent electrical insulation and light transmitting properties (eg, quartz). In FIG. 1, 30 and 31 are electrode terminals attached to the press base 19 and the punch 22, respectively,
An electric current is made to flow in the pressurizing direction.

In the electric current sintering apparatus having the above-mentioned structure, the punch 22 having the upper electrode 15 is pushed into the sintering die 11 by the hydraulic ram 25 to press the conductive powder 12 and the electrode terminal 30, A voltage is applied to 31 to cause a current to flow through the conductive powder 12 to generate heat. The powder compact 13 is heated by the Joule heat due to the heat generated by the conductive powder 12, and is further pressed by the punch 22. On the other hand, the interposition of the coating 14 can prevent the conductive powder from directly reacting with the powder compact or adhering to the surface. In addition, since the coating film 14 is made of a material that does not react with the powder compact 13, the coating film 14 is heated by the electric current so that the compact body 13 can be heated.
It rarely adheres to the surface by sintering.

The applied voltage, the magnitude of the electric current, and the energizing time in the energization heating are appropriately selected depending on the constituent material of the powder compact 13, the sintering temperature and the like. In the apparatus shown in FIG. 1, an optical temperature measuring sensor 29 is installed so as to face the transparent window 28 of the sintering die 11, and the applied voltage and the energization time are adjusted according to the heat generation of the conductive powder 12. be able to. In addition,
When a conductive powder that is easily oxidized, such as carbon, is used as the conductive powder, even if an inert gas is flown into the sintering mold as in the conventional energization sintering device (FIG. 3). Good.

After heating by energization for a predetermined time, the punch 22 is pulled up and the powder compact 13 is taken out from the sintering die 11.
The taken out powder compact 13 is sintered into a high density sintered compact. When the coating material does not react with the conductive powder and has excellent releasability, the coating can be easily removed from the powder compact after sintering. When the conductive powder adheres to the recesses on the surface of the powder compact together with the coating,
It may be removed by sandblasting or the like.

Next, another embodiment of the electric current sintering apparatus for carrying out the sintering method of the present invention will be described with reference to FIG. Figure 2
The current-flowing sintering apparatus shown in FIG. 1 uses a so-called dry type cold isotropic pressing method in which a sintering die 33 made of an elastic material such as resin or rubber is pressurized with a fluid flowing around the sintering die 33. It was used. Pressurization chamber 34 through which fluid as a pressurizing medium flows
Is a space defined by a cylindrical container 35 and an elastic film body 36 that is airtightly mounted inside the cylindrical container 35 with a seal holding member (for example, a backup ring) 37. A fluid introducing hole 38 for introducing the fluid into the pressurizing chamber 34 penetrates the cylindrical container 35. The sintering die 33 is fitted inside the elastic film body 36. Ring-shaped lids 39 and 40 are provided on the upper and lower portions of the sintering die 33, respectively. Insulators 43, 4 are provided in the holes of the ring-shaped lids 39, 40, respectively.
The current-carrying electrode plugs 41 and 42 are fitted and inserted through the connector 4. Breathable electrodes 45 and 46 are detachably attached to the tip ends of the energizing electrode plugs 41 and 42 on the side of the sintering mold 33 by a screw structure or the like, and wear due to the conductive powder or the air permeability is lowered. Can be replaced in case.
A vent hole 47 penetrates through the upper electrode plug 41 for energization, so that gas generated in the energization sintering process can be released to the outside. In FIG. 2, reference numeral 48 is a conductive powder, and a powder compact 49 having a coating 50 is embedded in the conductive powder 48.

In the electro-sintering apparatus having the above structure, the conductive powder 48 is applied by pressurizing the sintering die 33 with the pressure of the fluid flowing through the pressurizing chamber 34 and applying a voltage.
Heat up. The powder compact 49 is heated by the heat generated by the conductive powder 48, and is pressed by the fluid, so that the powder compact 49 is sintered. The applied voltage, the magnitude of the current, and the energization time in the energization heating are appropriately selected depending on the constituent material of the powder compact 49, the sintering temperature, and the like. Is selected within a range that does not cause burnout of the above and damage of the breathable electrodes 45 and 46. Specifically, it is preferable to control the electric current so that the sintering is carried out for an energization time of about 1 to 30 seconds. Depending on the type of powder compact, one cycle from filling the conductive powder to taking out the powder compact can be performed in about 1 to 60 seconds.
Further, the method using the apparatus shown in FIG. 2 applies pressure from the radial direction of the sintering die 33, and is therefore suitable for sintering a slender powder compact in the axial direction.

In the sintering apparatus shown in FIG. 2, a ceramic felt, a cloth or other heat insulating material is attached to the inner wall surface of the sintering die 33 to prevent the sintering die 33 from being burned during electric current sintering. Can be prevented. It is also possible to attach a temperature measuring sensor that can measure the temperature in the sintering die in a non-contact manner and adjust the applied voltage and the energization time according to the temperature.

[0022]

In the method for sintering a powder compact according to the present invention, the film and the powder compact do not react with each other due to the electric current sintering. It is possible to obtain a sintered product of a powder compact having no adhered particles. Therefore, it is a powder compact composed of various sinterable metals, ceramics, and composite material powders, and has a complex shape, elongated rod shape, or cylindrical shape having irregularities formed by MIM (metal injection molding method). The body can be densely sintered in a short time.

Further, in the method for sintering a powder compact of the present invention, the reaction and adhesion of the conductive powder and the powder compact can be prevented by the interposition of the coating film, so that the selection range of the conductive powder to be used is conventionally. Will be wider than.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an electric sintering apparatus for carrying out the method for sintering a powder compact of the present invention.

FIG. 2 is a view showing another embodiment of an electric sintering apparatus for carrying out the method for sintering a powder compact of the present invention.

FIG. 3 is a view showing an electric sintering apparatus for carrying out the conventional method for sintering a powder compact.

[Explanation of symbols]

 11 Sintering Type 12 Conductive Powder 13 Powder Forming Body 14 Coating 15 Upper Electrode 16 Lower Electrode 32 Temperature Measuring Sensor 33 Sintering Type 34 Pressurizing Chamber 48 Conductive Powder 49 Powder Forming Body 50 Coating

Claims (1)

[Claims] 1. A coating film made of a material that does not react with the compact is formed on the surface of the powder compact, which is made of sinterable powder.
A molded body having the coating is embedded in a conductive powder filled in a sintering die, the conductive powder is pressed, and a voltage is applied to the conductive powder to generate heat to sinter the molded body. A method for sintering a powder compact, comprising: