JPS62138376A - Silicon carbide base composite material and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a silicon carbide-based composite material and a method for producing the same, and in particular, the present invention relates to a silicon carbide-based composite material and a method for producing the same. The present invention relates to a silicon carbide composite material with excellent sliding properties and wear resistance, and a method for producing the same.

[Conventional technology]

Silicon carbide sintered bodies generally have extremely excellent chemical and physical properties, so they are used in sliding parts such as mechanical seals and bearings, and pumps for highly corrosive solutions such as acids and alkalis. It is known to be an excellent material for parts.

By the way, silicon carbide has high hardness and excellent wear resistance, but it has the disadvantage of poor self-lubricating properties, which makes it difficult to use ordinary lubricants, especially in high temperature ranges or in vacuum. When used as a sliding member under such harsh conditions, it has been difficult to fully demonstrate its excellent properties.

Therefore, as a material for solving the above-mentioned problems, rSiC, Si, and
or 3 to 50 wt of BN or carbon to Sialon.
% is added to the ceramic," is disclosed.

[Problem that the invention seeks to solve]

However, the ceramics described in JP-A-80-21884 are manufactured by mixing BN or carbon, which serves as a solid lubricant, with the starting materials at a stage before sintering, shaping the mixture, and then firing it. Since a solid lubricant exists between the ceramic particles, it is difficult to bond the ceramic particles to each other during sintering, and it is particularly difficult to form a high-strength ceramic. .

[Means for solving problems]

As a result of various studies aimed at solving the above-mentioned problems, the present inventor discovered that although a porous body has a relatively large number of open pores, it has extremely high strength porous bodies. By newly discovering the silicon carbide sintered body and filling the open pores of the porous silicon carbide sintered body with carbon that can impart lubricity, we have achieved extremely high sliding properties and wear resistance. We have come up with the idea that it is possible to produce a composite material that is excellent and can be sufficiently applied even under extremely harsh conditions such as high temperatures or vacuum.
The invention has been completed.

The present invention has an open porosity of 10 to 60% by volume, an average pore diameter of 0.1 to 200 μm, and an average crystal aspect ratio of 3 to 60% by volume.
The present invention relates to a silicon carbide composite material in which open pores of a porous silicon carbide sintered body of No. 50 are filled with carbon, and a method for manufacturing the same.

Hereinafter, the silicon carbide composite material of the present invention will be explained in detail.

The silicon carbide composite material of the present invention needs to be one in which open pores of a porous silicon carbide sintered body are filled with carbon. The reason for this is that silicon carbide sinter itself has poor self-lubricating properties, so it is extremely difficult to apply silicon carbide sintered bodies as a sliding material, especially in the absence of a lubricant. By filling the open pores of a porous silicon carbide sintered body with carbon, which can function as a lubricant, a composite material with extremely excellent sliding properties and wear resistance can be created. Because it can be done.

The porous silicon carbide sintered body of the present invention has an open porosity of 10 to
It is necessary that it be 60% by volume. The reason for this is that it is difficult to produce porous silicon carbide with a low open porosity and a low IO volume increase.On the other hand, if the open porosity is higher than 60 volume%, the strength of the sintered body is low and the silicon carbide particles This is because it is easy to detach.

The porous silicon carbide sintered body of the present invention has an average pore diameter of 0.1
~200pm is required. The reason is that if the average pore diameter is smaller than 0.1 μm, it is extremely difficult to fill with carbon;
This is because if the size is larger, the strength of the porous silicon carbide sintered body will be low, and the carbon filled in the porous silicon carbide will easily fall off.

The porous silicon carbide sintered body of the present invention needs to have an average crystal aspect ratio of 3 to 50. The reason is,
This is because by setting the aspect ratio of the crystal to 3 or more, the ratio of pores constituted by silicon carbide crystals to the sintered body can be relatively increased.On the other hand, when the average aspect ratio is 50 or more, This is because if the sintered body is large, there will be fewer joints between crystals, and the strength of the sintered body itself will be lowered. In addition, it is more advantageous that the average aspect ratio is 5 to 30.

The porous carbonized sintered body of the present invention preferably has an average length in the long axis direction of the crystals of 0.5 to 200 ILm.
The reason for this is that it is difficult to produce a porous silicon carbide sintered body consisting of crystals with an average length in the major axis direction of less than 0.5 μm and an average aspect ratio of 3 or more; This is because if the length is longer, stress tends to concentrate at the joints of the crystals, and the strength of the sintered body itself is low.

The average length of the crystal in the long axis direction is 1 to 150 JLl.
It is more advantageous that

Note that the pore diameter as used in the present invention is the arithmetic average value of the maximum length in the long axis direction of each pore observed in an arbitrary cross section of the sintered body and the maximum length in the direction perpendicular to the long axis direction. can be,
The aspect ratio (R) of a crystal is the ratio of the length (X) in the long axis direction of each crystal similarly observed to the maximum length (Y) in the direction perpendicular to the long axis direction, that is, R= X/
It is represented by Y.

The carbon filled in the silicon carbide composite material of the present invention is preferably graphitic. The reason for this is that graphitic carbon has a very remarkable effect of imparting lubricity, and can be made into a silicon carbide composite material with excellent sliding properties and wear resistance. The silicon carbide composite material of the present invention is
It is preferable that at least IO volume part of carbon is filled with respect to 100 volume open pore volume of the porous silicon carbide sintered body. The reason for this is that if the carbon filling amount is less than 10 parts by volume, it is difficult to obtain sufficiently good sliding characteristics and wear resistance.

Next, a method for producing a silicon carbide composite material according to the present invention will be explained.

The manufacturing method of the second invention of the present invention is characterized in that it consists of the following steps (a) to (c). A method for manufacturing a silicon carbide-based composite material comprising carbon filled in the open pores of a porous silicon carbide sintered body having an average aspect ratio of 3 to 50.

(a) A step of mixing silicon carbide powder with an average particle size of 1101 L or less, a sintering aid, and a forming aid, and molding it into a formed body of a desired shape: (b) A step of mixing the silicon carbide powder with an average particle size of 1101 L or less, a sintering aid, and a forming aid, and molding it into a formed body of a desired shape. (c) the step of heating and sintering the formed body at a temperature of 1800 to 2300°C in a non-oxidizing atmosphere to form a porous silicon carbide sintered body; (c) the above (
Filling the open pores of the porous silicon carbide sintered body obtained in step b) with a carbonaceous substance, and then heating the carbonaceous substance to a temperature of 700 to 2300°C in a non-oxidizing atmosphere to carbonize the carbonaceous substance. Process.

Further, the manufacturing method of the third aspect of the present invention is characterized by comprising the following steps (a) to (c), wherein the open porosity is 20 to 60% by volume, the average pore diameter is 20 to 200 μm, A method for manufacturing a silicon carbide-based composite material in which open pores of a porous silicon carbide sintered body having an average crystal aspect ratio of 3 to 50 are filled with carbon.

(b) A step of mixing silicon carbide powder with an average particle size of 10 pm or less and a molding aid and molding it into a green body with a desired shape; (b) Non-oxidizing the green body obtained in step (a) above. (c) step of heating and sintering at a temperature of 1800 to 2300°C in a neutral atmosphere to form a porous silicon carbide sintered body; (c) the above (
B) Fill the open pores of the porous silicon carbide sintered body obtained in the step with a carbonaceous substance, and then heat the carbonaceous substance to a temperature of 700 to 2300°C in a non-oxidizing atmosphere to carbonize the carbonaceous substance. Process.

It is.

In particular, the manufacturing method of the second invention of the present invention has an open porosity of 10
This is a method for producing a volumetric silicon carbide sintered body of ~60% by volume, and the formed body is a mixture of silicon carbide powder with an average particle size of 10 pLm or less, a sintering aid, a carbonaceous additive, and a forming aid. However, it is necessary that the product is obtained by the step (a) of molding it into a formed body having a desired shape, and the manufacturing method of the third invention particularly requires a porous carbonized material having an open porosity of 20 to 60% by volume. This is a method for producing a silicon sintered body, and the green body is obtained by the step (a) of mixing silicon carbide powder with an average particle size of 10 pm or less with a forming aid and molding the mixture into a green body with a desired shape. It needs to be something.

In the manufacturing method of the second invention and the manufacturing method of the third invention, the reason why it is necessary that the average particle size of the silicon carbide powder is IOpm or less is that the powder with an average particle size of 10pm or less is There are relatively many contact points between particles,
In addition, the thermal activity at the firing temperature is high, and the diffusion movement of atoms between silicon carbide particles is significant, so bonding between silicon carbide particles is extremely likely to occur, resulting in a sintered compact with high strength even at a relatively low density. This is because it is possible to obtain In particular, it is advantageous for the silicon carbide powder to have an average particle size of 5 JLm or less.

Incidentally, the crystal types of silicon carbide include α type crystal, β type crystal and amorphous type, and according to the present invention, the silicon carbide powder contains at least 30% β type crystal silicon carbide.
It is preferable to use silicon carbide powder that contains β-type crystals, because β-type crystals are low-temperature stable crystals that are synthesized at relatively low temperatures, and bonding between silicon carbide particles easily occurs during sintering, resulting in a relatively low density. However, a silicon carbide powder containing 50% or more of β-type crystals is especially advantageous because a high-strength crystalline body can be produced.

In the manufacturing method of the second aspect of the present invention, the reason why the sintering aid is mixed is to improve the bonding between silicon carbide particles during sintering and to form a three-dimensional network of relatively fine silicon carbide crystals. This is to produce a bonded sintered body. As the sintering aid, any material that can generate vapor of the sintering aid and/or vapor of decomposition products during firing of the formed body can be suitably used, and among them, boron, aluminum, etc. It is preferable to use at least one selected from , iron, chromium, lanthanum, titanium, yttrium, erbium, or compounds thereof.

Advantageously, the content of the sintering aid is between 0.01 and 10% by weight. The reason for this is that if the content of the sintering aid is less than 0.01% by weight, the above-mentioned effects cannot be fully exhibited, while if it is more than 10% by weight, This is because although the effect does not change much, the amount remaining in the sintered body increases and the original characteristics of silicon carbide deteriorate. In addition, it is more advantageous that the content of the sintering aid is 0.02 to 5%.

The molding aid used in the manufacturing method of the second invention and the manufacturing method of the third invention of the present invention is used as a lubricant or a binder during molding by being blended into the powder. Among the above-mentioned molding aids, carpo wax, magnesium stearate, barium stearate, aluminum stearate, zinc stearate, stearic acid, cellulose acetate, glycerin, polyethylene glycol, etc. can be used as those having a partial layer effect. Examples of substances that have a binding effect include starch, dextrin, gum arabic, casein, sugars, H
a-carboxymethylcellulose, methylcellulose,
Cellulose acetate, glycerin, polyvinyl alcohol,
Polyvinyl methyl ether, polyacrylic acid amide, polyethylene glycol, tannic acid, liquid paraffin,
Wax emulsion, ethyl cellulose, polyvinyl acetate, phenol resin, etc. can be used, and these can be used alone or in combination.

According to the manufacturing method of the second invention and the manufacturing method of the third invention of the present invention, any of α-type crystals, β-type crystals, and amorphous silicon carbide can be used, but especially high-strength silicon carbide can be used. In order to produce a porous silicon carbide sintered body, it is preferable to use silicon carbide powder containing at least 30% by weight of β-type crystalline silicon carbide, especially silicon carbide powder containing 50% by weight or more. It is preferable that

According to the manufacturing method of the second aspect of the present invention, the formed body obtained in the step (a) is heated for 1800 min in a non-oxidizing atmosphere.
It is necessary to sinter it by heating to a temperature of ~2300°C to form a porous silicon carbide sintered body. The temperature is 1800~
The reason why the temperature is set within the range of 2300°C is that at a temperature lower than 1800°C, bonding between silicon carbide particles and grain growth are insufficient, making it difficult to obtain a sintered body with high strength. If the temperature is too high, the sublimation of silicon carbide will increase, and the neck of the developed crystal will conversely become thinner, making it difficult to obtain a silicon carbide sintered body with high strength.

On the other hand, according to the manufacturing method of the third aspect of the present invention, the formed body obtained in the step (a) is heated in a non-oxidizing atmosphere.
It is necessary to sinter it by heating to a temperature of 900 to 2300°C to form a porous silicon carbide sintered body. The temperature is 19
The reason why the temperature is set in the range of 00 to 2300°C is that at a temperature lower than 1900°C, the bond between silicon carbide particles and the growth of the particles are insufficient, making it impossible to obtain a sintered body with high strength. If the neck size is higher than that, the necks that have grown once are smaller than a certain size will become constricted, or in severe cases they will disappear, resulting in a decrease in strength, and some particles will become coarser. This is because the roughness of the surface deteriorates.

According to the invention, in order to produce a porous silicon carbide sintered body having relatively large open pores, the heating rate during firing should be relatively slow, and the maximum temperature should be relatively high. It is advantageous to increase the temperature and/or the holding time at the maximum temperature. Under these conditions, individual silicon carbide plate crystals can be grown to a large size, and as a result, a porous silicon carbide sintered body having large open pores can be manufactured. On the other hand, in order to produce a porous silicon carbide sintered body having relatively small open pores, the heating rate during firing must be relatively fast, the maximum temperature must be relatively low, and/or the maximum temperature must be maintained. It is advantageous to shorten the time. According to these conditions, a porous silicon carbide sintered body can be manufactured without growing individual silicon carbide plate crystals to a large extent.

According to the manufacturing method of the second invention and the manufacturing method of the third invention of the present invention, the open pores of the porous silicon carbide sintered body are filled with a carbonaceous material, and then in a non-oxidizing atmosphere,
It is necessary to carbonize the carbonaceous material by heating to a temperature of 2300°C. The reason is that the silicon carbide sintered body itself has poor self-lubricating properties, so it is extremely difficult to apply the silicon carbide sintered body as a sliding material, especially under conditions where no lubricant is present. By filling the open pores of the porous silicon carbide sintered body with carbon, which has self-lubricating properties and can act as a lubricant, extremely excellent sliding characteristics and wear resistance are achieved. This is because it can be made into a composite material having

According to the present invention, it is preferable to use the carbonaceous material that can leave as much carbon as possible during carbonization, and it is preferable that at least 5% by weight of carbon can be left behind. The amount of carbon remaining is 5
This is because if a carbonaceous material smaller than % by weight is used to fully fill the open pores with carbon, filling and carbonization of the carbonaceous material must be repeated many times, which is not economical. .

Examples of the carbonaceous substances include unsaturated polyester resins, epoxy resins, phenol resins, furan resins, diallyl phthalate resins, urea resins, melanin resins, xylene resins, polyimide resins, polyurethane resins, polydivinylbenzene resins, and aromatic compounds. A condensed polycyclic polynuclear aromatic resin using heavy oil or tar/pitch, heavy oil, tar/pitch, polyvinyl chloride, etc. can be used. Note that among the carbonaceous substances, heavy oil,
It is advantageous to use tar pitches and polyvinyl chloride after subjecting them to infusibility treatment, if necessary.

Further, the temperature at which the carbonaceous material is carbonized is set to 700 to 230.
The reason why the temperature is set at 0°C is that if the temperature is lower than 700°C, carbonization of the carbonaceous material tends to be insufficient and it is difficult to form carbon with excellent lubricity. In order to further improve lubricity through graphitization, it is preferable to increase the temperature as much as possible, but if the temperature is higher than 2300°C, decomposition of silicon carbide will occur.

According to the present invention, carbon powder, graphite powder, or carbon fiber that has been carbonized in advance may be mixed with the carbonaceous material.

Next, the wooden invention will be explained with reference to examples.

11. The average particle size is 0.28 JLm, and the content of β-type crystals is 94.
For 100 parts by weight of 6% by weight silicon carbide powder, 0.3 parts by weight of boron carbide powder, 5 parts by weight of polyvinyl alcohol,
300 parts by weight of water was added, mixed in a ball mill for 5 hours, and then spray-dried. The silicon carbide powder contains 0.28% by weight of carbon, 0.17% by weight of oxygen, and 0.0% of iron.
It contained 0.03% by weight of aluminum and 0.03% by weight of aluminum.

Collect an appropriate amount of this dried material and charge it into a mold.

Pressure molding was performed at a pressure of 3000 kg/crn' to obtain a green body.

Next, this formed body was fired in an argon gas atmosphere at 2100°C, and the density was 2.88 g/am'', the average pore diameter was 3 pm, the average crystal aspect ratio was about 8.5, and the strength was 39 kgf/mm'. A porous silicon carbide sintered body having open pores uniformly dispersed in three dimensions was obtained.The open porosity was about 17% by volume.

Next, the open pores of this porous silicon carbide sintered body were impregnated with high pitch having a melting point of 110° C. and capable of leaving 52% by weight of carbon during carbonization. This high-pitch impregnation is carried out by first heating the pitch to 120°C under vacuum and holding it for 1 hour to degas the pitch, then immersing the porous silicon carbide sintered body heated in vacuum to 200°C, and then 20
The temperature was raised to 0°C, held for 1 hour, and then pressurized to 10 atm.

After immersing the porous silicon carbide sintered body impregnated with high pitch as described above in concentrated nitric acid, coke powder (#60) was added.
Silicon carbide composite material I got it.

The ratio of carbon to the open pores of the obtained silicon carbide composite material was 42% by volume.

After processing this composite material into a ring shape with an inner diameter of 15 mm, an outer diameter of 21 mm, and a thickness of 5 mm, a silicon carbide sintered body (porosity 2%) was processed in water using a ring-on-ring sliding tester.
) was used as a mating material and a sliding test was performed, and the limit pv value was 14,500 kgf/crrf-m/a+in, the friction coefficient was 0.005, and the specific wear rate was 7.
It was observed that there were 8 x 10 (- ``fair'') animals.

2.1 Composite materials were obtained in the same manner as in Example 1, except that the sintering temperature of the formed body and the carbonization temperature of the high pitch were varied as shown in Table 1.

The properties of the obtained composite material and the sliding properties measured in the same manner as in Example 1 are shown in Table 1.

As can be seen from the results shown in Table 1, all of the composite materials of this example were found to have excellent sliding properties. On the other hand, the porous silicon carbide sintered body obtained in Example 1 was exposed to air at 600°C in the case of the sintered body of Comparative Example 1-1. 1. After heating for 1 hour to introduce oxygen-containing functional groups onto the surface, the benzene-soluble content of petroleum pitch (average molecular weight 340) with a softening point of 80°C and P-xylylene glycol were mixed in a molar ratio of 1:2. 1% by weight.
A B-stage resin prepared by reacting a mixture of P-) luenesulfonic acid at 130°C for 40 minutes was immersed in a liquid melted at 150°C, and then cured at 300°C for 10 hours.

The resin-filled porous silicon carbide sintered body obtained as described above was carbonized in the same manner as in Example 1 to obtain a silicon carbide composite material.

The properties of the obtained composite material and the sliding properties measured in the same manner as in Example 1 are shown in Table 1.

As can be seen from the results shown in Table 1, the composite material of this example was found to have extremely excellent sliding properties.

Dry granules were obtained in the same manner as in Example 1, but without adding boron carbide.

Take an appropriate amount of this dry mixture, charge it into a mold, and
A green body was obtained by pressure molding at a pressure of 0.00 kg/cm''.

The formed body was placed in a graphite crucible and fired in a Tammann type firing furnace in an atmosphere of mainly argon gas at 1 atm. In the temperature raising process, the temperature was raised to 2200°C at a rate of 450°C/hour, and the maximum temperature of 2200°C was maintained for 10 minutes. The CO gas partial pressure during sintering is 80 Pa or less at room temperature to 1700℃,
The argon gas flow rate was appropriately adjusted and controlled so as to be within the range of 300±50 Pa in a high temperature range higher than 1700°C.

The density of the obtained sintered body was 2.05 g/cm', and its crystal structure was observed using a scanning electron microscope.
It had a three-dimensional structure in which silicon carbide plate crystals with an average aspect ratio of 11.3 were intricately intertwined in multiple directions, and the average bending strength of this sintered body was as high as 12 kg/mrn'.

Strut 1" A composite material was obtained in the same manner as in Example 4, except that high pitch impregnation and firing were carried out twice to improve the carbon filling rate.

The properties of the obtained composite material and the sliding properties measured in the same manner as in Example 1 are shown in Table 1.

〔Effect of the invention〕

As described above, the silicon carbide composite material of the present invention is a porous silicon carbide sintered body having three-dimensionally uniformly distributed fine open pores, and the open pores are filled with self-lubricating carbon. It exhibits extremely excellent sliding properties not only in the presence of water but also for applications such as pump parts and mechanical seals used in various heat media such as Freon. It exhibits sufficiently excellent sliding properties as a variety of sliding members used in high temperature ranges or harsh conditions such as vacuum where it is difficult to use normal lubricants, and it has a wide range of applications. It is a widely used material that can significantly improve the durability and reliability of equipment, and is extremely useful industrially.

that's all

Claims (1)

[Scope of Claims] 1) Open porosity is 10 to 60% by volume, and average pore diameter is 0.
A silicon carbide composite material comprising carbon filled in the open pores of a porous silicon carbide sintered body having crystals of 1 to 200 μm and an average aspect ratio of 3 to 50. 2) The silicon carbide composite material according to claim 1, wherein the carbon is graphitic. 3) The silicon carbide composite material according to claim 1 or 2, wherein the carbon is filled in at least 10 parts by volume per 100 parts by volume of open pores of the porous silicon carbide sintered body. 4) The silicon carbide composite according to any one of claims 1 to 3, wherein the porous silicon carbide sintered body has an average length in the long axis direction of the crystals of 0.5 to 200 μm. material. 5) Consisting of the following steps (a) to (c), the open porosity is 10 to 60% by volume and the average pore diameter is 0.1 to 60% by volume.
A method for manufacturing a silicon carbide-based composite material, in which open pores of a porous silicon carbide sintered body having a diameter of 100 μm and an average crystal aspect ratio of 3 to 50 are filled with carbon. (a) A step of mixing silicon carbide powder with an average particle size of 10 μm or less, a sintering aid, and a forming aid, and molding it into a formed body of a desired shape; (c) the step of heating and sintering the formed body at a temperature of 1800 to 2300°C in a non-oxidizing atmosphere to form a porous silicon carbide sintered body; (c) the above (
Fill the open porosity of the porous silicon carbide sintered body obtained in step b) with a carbonaceous material, and then heat it to a temperature of 700 to 2300°C in a non-oxidizing atmosphere to carbonize the carbonaceous material. The process of doing. 6) The silicon carbide powder contains at least 30% by weight of β-type crystal silicon carbide.
Manufacturing method described in section. 7) The manufacturing method according to claim 5 or 6, wherein the sintering aid is at least one selected from boron, aluminum, iron chromium, lanthanum, titanium, yttrium, erbium, or compounds thereof. . 8) The manufacturing method according to any one of claims 5 to 7, wherein the carbonaceous material leaves at least 5% by weight of carbon when carbonized. 9) The open porosity is 20 to 60% by volume and the average pore diameter is 20 to 2, characterized by the following steps (a) to (c):
A method for manufacturing a silicon carbide-based composite material, in which open pores of a porous silicon carbide sintered body having a diameter of 0.00 μm and an average crystal aspect ratio of 3 to 50 are filled with carbon. (a) A step of mixing silicon carbide powder with an average particle size of 10 μm or less and a molding aid and molding it into a green body of a desired shape; (b) A process of non-oxidizing the green body obtained by the above step (b). (c) step of heating and sintering at a temperature of 1900 to 2300°C in a neutral atmosphere to form a porous silicon carbide sintered body; (c) the above (
B) Fill the open pores of the porous silicon carbide sintered body obtained in the step with a carbonaceous substance, and then heat the carbonaceous substance to a temperature of 700 to 2300°C in a non-oxidizing atmosphere to carbonize the carbonaceous substance. Process. 10) The manufacturing method according to claim 9, wherein the silicon carbide powder contains at least 30% by weight of β-type crystal silicon carbide. 11) The carbonaceous material contains at least 5 carbon atoms during carbonization.
Claim 9 or 10 in which the percentage by weight remains
Manufacturing method described in section.