JPH11131106A - Method for producing sintered body by combustion synthesis and apparatus therefor - Google Patents

Abstract

(57) [Summary] In a sintered body production process based on a combustion synthesis reaction, a high-precision heat input is performed from outside the system to not only start the reaction, but also to preheat the reaction before pressurization under pressure. The present invention provides a constitution which makes it possible to supplement or compensate for heat during the reaction and to gradually cool the reaction product after the reaction. SOLUTION: The apparatus of the present invention includes a mold having an axial space limited by an electrically insulating and refractory material for accommodating and pressurizing a composition capable of causing a combustion synthesis reaction, and disposed around the mold. An induction coil for heating the composition, a pressurizing device for pressurizing and compressing the composition by axial pressurization,
Is included as a component. Also, an effective manufacturing method includes the following steps: (1) A starting material containing a mixture of raw material powders for combustion synthesis reaction formed to form a target compound and diamond powder is placed in an electrically insulating mold. (2) pressurizing the starting material, (3) energizing an induction heating coil arranged around the pressing die,
A step of igniting the compound raw material to start a combustion synthesis reaction, and (4) a step of pressurizing the combustion synthesis reaction product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a sintered body by combustion synthesis, and particularly to an apparatus therefor.

[0002]

2. Description of the Related Art A combustion synthesis method is used as a synthesis method for forming a high melting point compound or a compound requiring rapid cooling. In the combustion synthesis reaction, a high temperature locally exceeding usually 2000 ° C. is generated, and therefore, it is particularly suitable for producing a material containing a substance which is difficult to synthesize by a high-temperature reaction by external heating.

[0003] In the combustion synthesis reaction proposed so far, a green compact sample obtained by compacting a powder mixture of component elements is prepared, and the reaction is started by igniting one end of the sample. In the powder mixture, by the propagation of the combustion wave,
As the reaction progresses in a chain, the synthesis reaction is maintained by self-heating, and the compound is formed in a short time in seconds.

[0004] As described above, in the combustion synthesis method, various ceramics and intermetallic compounds can be synthesized in a very short time, but the products are used as various functional materials and structural materials. To do so, it is necessary to densify the reaction product by applying external pressure.

On the other hand, a disadvantage of this technique is that it is difficult to start and continue the reaction in a synthesis reaction using a combination of raw materials having a low heat of formation reaction, for example, in a system for synthesizing silicon carbide, boron carbide, tungsten carbide, or the like. Have been.

Under the circumstances described above, several proposals have been made regarding a method for producing a dense product by synthesis and simultaneous sintering, and a method for replenishing insufficient reaction heat in order to put the combustion synthesis method into practical use. .

As a method for densifying the material, combustion synthesis in HIP or forging immediately after the combustion synthesis reaction has been attempted in order to use a pressurizing operation simultaneously with or immediately after the reaction.

[0008] However, the former method is capable of heating for a long time under pressure, but cannot take advantage of the fact that the combustion reaction is completed in a short time, and has the disadvantage of high equipment and running costs. There is. The latter method, on the other hand, can take advantage of the short reaction time, but is disadvantageous in that it cannot be applied to the control of the pressurization speed / timing, the cooling process, or a system having a small reaction heat.

Regarding the method of replenishing the insufficient reaction heat, it is effective to use a mixed powder composed of a combination of elements that emit a large amount of heat upon combustion, that is, a so-called chemical oven, in order to make use of the characteristic of the short-time reaction. However, with this heating method using heat generated by a chemical reaction, it is difficult to control the amount of heat with high accuracy.

[0010] On the other hand, it is known to heat a work by induction heating in a hot press apparatus. However, usable works are limited to those in which softening of the raw material or appearance of a liquid phase can be expected, and a structure that can be effectively used in the above-described combustion synthesis process has not been known.

[0011]

DISCLOSURE OF THE INVENTION The present invention not only starts the reaction in the combustion synthesis reaction step by performing high-precision heat input from outside the system, but also performs preheating before the reaction under pressure and during the reaction. It is intended to provide a constitution which makes it possible to replenish or compensate for the heat of the reaction and to allow the reaction product to be gradually cooled after the reaction.

[0012]

SUMMARY OF THE INVENTION A first aspect of the present invention is as follows.
The present invention relates to a reactor which effectively solves the above-mentioned problem, and has a shaft-shaped space for containing and pressurizing a composition capable of causing a combustion synthesis reaction and limited by an electrically insulating and refractory material. Pressing die, an induction coil for heating the composition disposed around the pressing die, a pressurizing device for pressurizing and compressing the composition by axial pressing, as components, a combustion synthesis and pressurizing device. Make a summary.

The above apparatus can be effectively applied to the production of a sintered body containing diamond particles. Accordingly, a second aspect of the present invention is directed to a method for manufacturing such a sintered body, comprising the following steps. (1) A step of loading a starting material containing a raw material powder for combustion synthesis reaction formed to form a target compound and a diamond powder into an electrically insulating mold; (2) adding the starting material Pressurizing, (3) a step of igniting a compound raw material by energizing an induction heating coil disposed around a pressing die to start a combustion synthesis reaction, and (4) a step of pressurizing a combustion synthesis reaction product.

Therefore, the above-mentioned apparatus of the present invention has an advantage that the reaction can be induced and continued by supplying heat to a system having a small reaction heat while maintaining the characteristics of combustion synthesis which is a short-time process. In addition, in the combustion synthesis reaction, to improve the wear resistance of the surface of the reaction product, or to impart a special function, it may be desirable to contain super abrasive grains such as diamond, At this time, since diamond essentially acts as a diluent, its high concentration often results in a shortage of required calorific value, and in the end, the conventional combustion synthesis process sometimes makes it difficult to maintain the reaction. The heat supply by induction heating according to the present invention is particularly effective in forming such a sintered body having a high diamond concentration.

In addition, in the apparatus of the present invention in which a combustion synthesis reaction is performed under a pressurized state, a denser sintered body can be formed as compared with the conventional method. That is, in the ignition and pressurization method using the conventional combustion synthesis apparatus, it was not possible to use a dense green compact in order to limit the dissipation of the reaction heat and propagate the combustion wave. Since heat can be supplied from the outside even during the reaction, even a compact compact such as a CIP molded product can be subjected to combustion synthesis.

As described above, in the combustion synthesis method, since the reaction is completed in a short time of the order of seconds, it is most suitable for sintering a metastable substance under normal pressure such as diamond.

In the reactor of the present invention, the induction heating method is used for heating the sample, so that there is no need for a wiring for electric ignition and a heater which are inevitable in the conventional combustion synthesis apparatus and lead to the sample chamber. In this regard, the assembly of the pressurized mold has been facilitated. Moreover, it is easy to adopt a configuration in which the reaction system is shut off from the outside air as described below, whereby the reaction can be performed in an inert gas atmosphere or a reduced pressure atmosphere.

For example, in the present invention, the reaction is carried out in a nitrogen atmosphere in order to prevent the formation of nitrides or oxides by-produced, or the gas released during the combustion synthesis reaction is rapidly reduced. Skin removal can be performed under reduced pressure for removal.In this case, the periphery of the pressurized mold is surrounded by a sealed container made of insulating material such as quartz glass, and the sliding portion with the pressurizing piston is For example, a vacuum seal using an O-ring can be easily separated from the external atmosphere.

In addition, since a densification step by forging immediately after the combustion synthesis reaction, which has been conventionally performed, is not required, an ordinary pressure press is sufficient as a pressure device.

The induction heating of the present invention is applied to a process utilizing heat of reaction generated when a mixed powder formed to produce combustion synthesis produces a target compound, and the reaction is started (the powder is not heated). Ignition), and as a heat source for replenishing the amount of heat insufficient for maintaining the reaction. Heating the thermally neutral mixed powder to the sintering temperature is not the object of the present invention.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, in order to manufacture a sintered body by combustion synthesis, a pressing die for accommodating a green compact of a starting material is formed of an electrically insulating material, and an induction heating (for example, high frequency) coil is formed around the pressing die. And ignite or preheat the green compact. At this time, in order to enable or improve the current induction, if necessary, the surroundings of the green compact may be covered with a graphite sheet or graphite powder, or a metal material may be disposed in contact with the green compact. it can.

When quasi-isostatic pressing is required, an insulating granular solid (eg, molding sand) is placed in a cylindrical pressure-resistant and heat-resistant insulating container (eg, a ceramic sintered body such as sintered alumina).
, And the assembled sample is disposed therein. Under high pressure through the granular solid pressure medium, ignition is performed by high-frequency induction heating to start a combustion synthesis reaction. In this case, the sample is arranged at a position where the high-frequency current can flow most efficiently.

In the above, the graphite sheet placed around the green compact sample is not only effective for induction heating of the sample, but also
In addition, the formed reaction product is easily removed from the pressing die, contamination by a high-temperature chemical reaction with a granular solid pressure medium used for quasi-isotropic pressing, and mechanical reaction due to biting of the pressure medium particles. It is also effective in preventing reaction products such as contamination.

Furthermore, since a reducing atmosphere is formed inside the graphite sheet during the reaction, this structure is suitable for handling a transition metal source which is easily oxidized, or for a thermodynamically metastable diamond. It is particularly suitable when performing heat sintering of

The pressurization of the sample is usually suitably performed by a uniaxial pressurized hydraulic press. However, in order to ensure electrical insulation, an electrically insulating material is disposed around the distal end of the pressurizing piston, or at least this portion of the piston is made of an insulating material. In addition, by providing a water cooling device as needed, it is possible to prevent the piston from being ignited by the induction heating and the strength from being reduced.

Although the apparatus of the present invention can be used as a small-scale production facility for high-mix low-volume production, the following can be used as an example of a suitable pressurizing / heating apparatus combined in this case. it can. That is, as the specification of the press for pressing,
Work table size 350 × 700mm, piston stroke 300mm, piston descending speed: 30m at high speed
m / s, 5 mm / s at low speed, 30 tons of pressurizing load, and a variable power supply with a frequency of 60 to 120 Hz, an output voltage of 50 to 200 V, and an output current of 100 to 200 A are suitable as specifications of the high frequency power supply.

Next, embodiments of the present invention will be described with reference to the accompanying drawings.

[0028]

Example 1 Using a molding die having a cylindrical space with an inner diameter of 50 mm, a superhard mixed powder of WC-10% Co was molded into a disk-shaped pellet having a thickness of 5 mm. Separately, Ti: C: Co / 10/20 μm diamond =
The diamond-containing mixed powder of 48: 12: 5: 35 was molded into a disk-shaped pellet having a thickness of 10 mm. Using these pellets, a sintering reaction was carried out by an apparatus configuration as schematically shown in FIG.

The cemented carbide pellets 10 and the diamond-containing pellets 11 were stacked to form an integral product, and the periphery thereof was further wound twice with a graphite sheet 12 having a thickness of 1 mm. In order to prevent the pressurized medium (casting sand) from adhering, disc-like graphite sheets 13 and 14 each having a diameter of 50 mm and a thickness of 1 mm were respectively arranged on the upper and lower surfaces of the pellet aggregate to form a reaction aggregate.

This assembly was loaded into the reactor 15 and a combustion synthesis and densification reaction was performed. Inside diameter 6 placed on bottom 16
The press table 18 is filled into a 5 mm sintered silicon nitride mold 17, and a 5 ton load is applied from a mullite push rod 19 via a molding sand 20 as a pressure medium by a hydraulic press (not shown). added.

Next, about 75 kHz, about 9
When an electric power of 0 V and about 150 A is applied to the coil 21, an induced current flows through the coated graphite sheet around the sample,
The combustion reaction is induced by the local heating due to the strong heat around the sample in contact with the graphite sheet, and the skin generated at the tip of the combustion wave propagates toward the center.
Was estimated to have been reached. Turn off the high frequency power at this point,
After the pressurization was continued for 30 seconds, the reaction product was removed.

The obtained product is a sintered body in which a hard layer in which about 40% by volume of diamond is dispersed in a TiC—Co matrix is baked on a cemented carbide base. After being cut by electric discharge machining and polished with a diamond whetstone, it was finished into a router blade for wood processing.

[0033]

Embodiment 2 An outer diameter of 75 mm and a height of 70 shown in FIG.
A 0.25 mm-thick graphite sheet 26 was attached to the inner wall using an alumina pressing die 25 having an inner diameter of 26 mm and an apex angle of 60 ° at the tip, and then Ti: B: N at the tip.
i: 30/40 μm diamond = 36: 8: 11: 45 (mass ratio) 8 g of mixed powder 27 was filled. Then 25 in diameter
mm race center base 28 (material: SK-3). A ceramic push rod 29 having a diameter of 25 mm was placed in contact with the bottom surface of the base 28, and a load of 1 ton was applied by a hydraulic press.

A high-frequency coil 30 having a diameter of 100 mm is arranged on the outer periphery of the pressing die, and is maintained at an output of 10 kW for 1 minute, thereby heating the base and igniting the mixed powder, thereby promoting the combustion and synthesis. The working layer, in which diamond was fixed in the matrix of the system, synthesized the material of the race center that was joined to the base.

[0035]

Embodiment 3 As shown in FIG. 3, a stamping die 3 made of sintered alumina having an outer diameter of 200 mm, a height of 150 mm, and an inner diameter of 77 mm.
5, a push rod 36 having a diameter of 75 mm and a length of 75 mm, and a push table 37 having the same diameter and a length of 25 mm were prepared. A graphite sheet 3 having a thickness of 0.25 mm in contact with the inner wall of the pressing die 35
8 and the push table 37 are inserted, and then a 40 μm S
90 g of pellets 39 of 28:12:60 (mass ratio) mixed powder of i powder, 10 μm C powder, and 200 mesh diamond powder were filled, and further, a diameter of 75 mm and a length of 50
The cemented carbide block 40 mm was put in, and the push rod 36 was filled in to form a starting assembly.

A high-frequency coil 41 having a diameter of 250 mm is arranged on the outer periphery of the pressing die 35, a load of 10 tons is applied by a hydraulic press, and the power is maintained at 20 kW for 2 minutes to form a pellet by heating the cemented carbide block 40. Was fired and the synthetic product was heated to produce a bit material for excavating a foundation pile hole in which a working layer made of a SiC-diamond sintered body was joined to a cemented carbide base.

[0037]

Example 4 The reaction apparatus shown in FIG. 4 was used. The hermetic reaction chamber 45 is defined by a side wall 46 made of heat-resistant glass having a hollow inner cylinder with an inner diameter of 200 mm, and a frame bottom plate 48 and a top plate 49 supported at intervals by columns 47. Stamping die 50
Is made of cylindrical alumina having an outer diameter of 150 mm, an inner diameter of 50 mm, and a height of 75 mm. The pressing rod 51 for pressing is made of mullite having a diameter of 47 mm and a length of 80 mm. The pressing table 53 is filled in the pressing die 50 placed on the bottom plate 52, and further, disc-shaped and sleeve-shaped graphite sheets 54 and 55 each having a thickness of 1 mm and a diameter of 50 mm are arranged on the bottom surface and the inner wall surface. ,
Si: Co: 20/30 μm diamond molded into a disk shape having a diameter of 47 mm and a thickness of 10 mm as a reaction material = 2: 1:
2 (mass ratio) pellets 56 were placed, and a 1 mm-thick graphite disk 57 was also arranged between the pellets 56 and the push rod 51.

The inside of the reaction chamber 45 is evacuated without applying a load to the push rod, and after a nitrogen atmosphere of 0.13 MPa is applied, a high-frequency coil 58 disposed outside the reaction chamber 45 is energized with an output of 15 kW. Graphite sheets 54, 55, 5
7, an induced current was induced, the reaction was started by heating the pellet 56, and a 2 ton load was applied to the push rod 51 to compress the pellet 56. After the pellet 56 was held for 1 minute, the heating and pressurization were stopped. .

The reaction product has a structure in which about 33 vol% of diamond particles are dispersed in a Si ₃ N ₄ —Co-based matrix. Used as a circular saw.

[0040]

【The invention's effect】

1. By using the induction heating method, the combustion synthesis reaction can be started and continued while the reaction material is pressurized. 2. By controlling the induction heating output, the sample temperature before, during, and after the reaction can be maintained at a required value through a graphite sheet or a cored bar. 3. Because of the induction heating method, the reaction start temperature of the sample can be controlled, and combustion synthesis can be performed even for a system having a small reaction heat. 4. The reaction vessel is housed in a pressure-resistant vessel and reacted under a pressurized gas, so that combustion synthesis is performed not only in the solid-solid reaction system used in the conventional combustion synthesis method but also in the solid-gas reaction system. It can also be used for reactions.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an apparatus configuration used in Embodiment 1 of the present invention.

FIG. 2 is a longitudinal sectional view of an apparatus configuration used in Embodiment 2 of the present invention.

FIG. 3 is a longitudinal sectional view of an apparatus configuration used in Embodiment 3 of the present invention.

FIG. 4 is a longitudinal sectional view of an apparatus configuration used in Embodiment 4 of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 Carbide pellet 11 Diamond-containing pellet 12 Graphite sheet 13, 14 Graphite sheet 15 Reactor 16 Bottom plate 17 Press mold 18 Press table 19 Push rod 20 Foundry sand 21 Coil 25 Press mold 26 Graphite sheet 27 Mixed powder 28 Race center base 29 Push rod 30 High frequency Coil 35 Stamping die 36 Push rod 37 Pushing stand 38 Graphite sheet 39 Pellet 40 Cemented carbide block 41 High frequency coil 45 Airtight reaction chamber 46 Heat-resistant glass side wall 47 Support column 48 Frame bottom board 49 Frame top 50 Pushing mold 52 Pushing bar 52 Bottom board 53 Pushing table 54, 55 Graphite sheet 56 Pellets 57 Graphite disk

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Goto 2-8-10, Midorikawachi-cho, Kawachi-gun, Tochigi Prefecture (72) Inventor Akira Hosomi 138-1 Inabago, Inabago, Oyama City, Tochigi Prefecture

Claims (4)

[Claims] 1. A mold having an axial space defined by an electrically insulating and refractory material, for accommodating and pressurizing a composition capable of causing a combustion synthesis reaction, and heating of the composition arranged around the mold. A combustion synthesis / pressurization apparatus comprising, as constituent elements, an induction coil for use in the present invention and a pressurizing apparatus for pressurizing and compressing the composition by axial pressing. 2. The apparatus according to claim 1, wherein the pressurization of the composition is performed by advancing a piston in the pressing die. 3. A method for producing a diamond-containing sintered body using a combustion synthesis / pressurization apparatus, comprising the following steps: (1) A raw material powder for combustion synthesis reaction formed to form a target compound Loading a starting material containing the mixture and diamond powder into an electrically insulating stamp, (2) pressing the starting material, and (3) energizing an induction heating coil arranged around the stamp. And (4) pressurizing the combustion synthesis reaction product by igniting the compound raw material and starting the combustion synthesis reaction. 4. The method according to claim 3, wherein, in the third step, the coil is continuously energized even after the start of the combustion synthesis reaction, and the amount of heat required to maintain the combustion synthesis reaction is supplemented by induction heating.