JPS62275063A - Manufacture of silicon carbide-aluminum nitride sintered product - 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 3. Detailed Description of the Invention Silicon carbide (a crystalline compound of silicon and carbon) has long been known for its hardness, strength and excellent resistance to oxidation and corrosion. Silicon carbide has a low coefficient of expansion, good thermal conductivity, and retains high strength at high temperatures. Recently, high-density silicon carbide compacts have been made from silicon carbide powder! l! The methods by which they have developed manufacturing techniques include reactive bonding, chemical vapor deposition, hot pressing, and pressureless sintering (in which the product is first shaped and then sintered). These methods are described in U.S. Pat. No. 3,853,566;
(, 852,099; 3,945.483 and 3
．． 96 (No. 1,577). The high-density silicon carbide compacts thus produced are excellent engineering materials that are subject to severe abrasion and operation under extremely high temperature conditions. It finds use in the fabrication of parts for turbines, heat exchange equipment, pumps, and other equipment or tools.

Various additives are used to obtain Xi silicon carbide ceramic materials with high density and surface strength. For example, a method of hot pressing silicon carbide to a density in the order of 98 percent of the theoretical density by adding aluminum and iron as densification aids has been proposed by 7 Ligro et al.
etal, J., Cheta, Soc.

Volume 39, No. 11, January 1965, 386-389)
It is written by. They found that dense silicon carbide could be produced from a powder mixture containing 1 weight percent aluminum. Their product has a temperature rating of 54°000 psi (3796k) at room temperature.
g/c+e2), 70.000 p at 1371°C
si (had a rupture coefficient of 4921 kg/cm2).

Aluminum nitride (a crystalline compound of aluminum and nitrogen) is widely used as a refractory material.

Aluminum nitride has excellent resistance to molten metal and is a particularly useful refractory for molten aluminum. Aluminum nitride has good thermal shock resistance, good strength, and excellent resistance to most chemicals.

By combining silicon carbide and aluminum nitride, improved high-performance materials can be processed into products that can withstand harsh operating conditions or into refractory materials that offer the strength of silicon carbide and the inertness of aluminum nitride. Many attempts have been made to produce dense materials. Such combinations have been proposed to improve the electrical conductivity of silicon carbide resistive elements and -) to improve the resistance of silicon carbide to corrosion at high temperatures. Examples of such mixtures are described in U.S. Pat. No. 3,259,509, 3.
287.478 and 3,492.153. However, previously proposed products are mixtures of silicon carbide and aluminum nitride that are not sintered to provide a dense co-sintered product. One disadvantage of aluminum nitride is that it is soluble in hot water. This property precludes the use of aluminum nitride in many applications that could otherwise be used advantageously. The mixtures proposed in the prior art do not substantially eliminate the solubility of aluminum nitride in hot water. now,
A co-sintered silicon carbide-aluminum nitride product containing up to about 45 percent aluminum nitride that has the useful properties of both silicon carbide and aluminum nitride and is substantially insoluble in hot water. It was discovered that it was difficult to manufacture.

The sinterable mixture of the present invention consists of silicon carbide, carbon and aluminum nitride. These mixtures are particularly suitable for use in pressureless sintering operations to provide hard, dense sintered ceramic products. The sintered ceramic product of the present invention has a co-sintered sintered ceramic product of about 0.5
It contains about 55 to 99.5 weight percent silicon carbide co-sintered with from 45 weight percent aluminum nitride. Final sintering! ! ! Although the article consists essentially entirely of co-sintered silicon carbide and aluminum nitride, it contains relatively small amounts, usually less than about 1.0 percent, of excess carbon or sintering aids, or sintering aids. Residues from the binder can be present without any adverse effects.

The theoretical density of silicon carbide is 3.21 g/e,c.

The sintered silicon carbide-aluminum nitride product of the present invention is! It has a density greater than 75% of theory and typically greater than 85% of theory.

Co-sintered ceramic articles having densities greater than 90 percent of theory can be produced by the present invention. Sintered products undergo approximately 10 percent shrinkage during the sintering process. The sintered product can be used in its as-sintered form, or it can be machined into complex shapes.

The components used to produce the sintered products of the present invention are silicon carbide, aluminum nitride and bondable carbon or bondable carbon source materials. Sintering aids such as boron or boron source materials may also be used to aid the sintering process. Generally, each component will contain from about 55.0 to about 99.0%.
0 weight percent silicon carbide, from about 0.5 to about 45. O
If percent fi amount of aluminum and about 0.5
The carbon is present in an amount ranging from about 6.0 weight percent to about 6.0 weight percent. When producing ceramic materials useful as bricks, crucibles, or furnace components, the starting composition usually contains a relatively large amount of aluminum nitride, ranging from about 3.0 to about 45.0 weight percent. It is preferable. For example, in the production of ceramic materials useful for the production of articles such as turbine blades or high temperature tools, the starting composition is typically about 90.0 to about 99.0
Contains a relatively large amount of silicon carbide in weight percent.

The sinterable mixtures of the invention are particularly suitable for use in pressureless sintering processes. In one method of the invention, the starting components are mixed, the mixture is cold pressed to form a green compact, and the green compact is then sintered to form a dense, hard product. . In another method,
Only the silicon carbide and carbon components are mixed, cold-pressed, and sintered in an atmosphere containing aluminum nitride. In both systems, the co-sintering of the silicon carbide and aluminum nitride components produces a hard vJL-dense product with the property of being insoluble in hot water.

The silicon carbide starting material is suitably selected from alpha or beta phase silicon carbide. Mixtures of alpha and 1 beta phase materials can also be used. The silicon carbide starting material of the present invention does not require phase separation or purification to obtain a sinterable material. Relatively small amounts of amorphous silicon carbide can also be included without adverse effects.

The silicon carbide starting material is preferably used in a finely ground state. Suitable finely ground materials are produced by grinding relatively large particles of silicon carbide, ball milling or jet milling, and then classifying or separating the components suitable for use in the present invention. Preferably, the silicon carbide starting material has a maximum particle size of about 5 microns and an average particle size of about 0°1 () to about 2.50 microns.The silicon carbide starting material has a particle size of less than about 1 micron. It is difficult to determine the exact particle size distribution for silicon powder, and therefore surface area appears to be relevant in determining a suitable material.Therefore, suitable silicon carbide particles for use in the present invention. is about 1 to about 1 (10m2
It has a surface area of 7H.

Within this range, the particles have a surface area of about 2 to about 501
A range of I2/g is preferred, and within that range, a range of about 2 to about 20+''/g has been found to be useful.

The aluminum nitride component of the present invention is preferably used in the form of a finely ground powder in order to be intimately combined with the other components. Preferably, particle sizes less than 5 microns are used, and more preferably less than about 2 microns. Aluminum nitride electric) & J for town R1,
When using [, it is necessary to enter the name of the
in the form of compacted pellets or bodies placed in a sintering furnace;
Just use it. Alternatively, aluminum nitride can be generated in-situ in a sintering furnace, but this method is difficult to control the amount of aluminum nitride in the product, and the furnace conditions are not suitable for sintering aluminum nitride. They are generally not preferred because of the problems of keeping them conductive both for manufacturing and manufacturing. One preferred method for providing an aluminum nitride atmosphere in the sintering furnace is simply by
Known in the sintering furnace! 1 is a shell aluminum nitride compressed body or pellet device, and the aluminum nitride is evaporated at the beginning of the sintering operation. Aluminum nitride is made by combining 75% by weight aluminum cum powder and 25% by weight aluminum heptadide with 80% nitrogen and 20% hydrogen.
It is suitable to produce it by nitriding at a temperature of 0.000C. 'A useful source of aluminum nitride can be obtained by appropriately pulverizing the M oxide and forming it into pellets. .

The compositions of the present invention can also contain excess or bound 1'IJtrP carbon in an amount of about 0.5 to about 6.0 weight percent. The carbon component facilitates the subsequent sintering operation and helps reduce the amount of oxides that may remain in the final product. In a preferred composition,
The binding rq'-capable carbon is present at about 2.0 to about 5.0 weight percent of the silicon carbide material. The carbon component can be used in any form that facilitates mixing of the carbon and silicon carbide components to achieve dispersion of the carbon throughout the mixture. If the carbon component is used in finely divided form, it is suitably in the form of colloidal graphite. However, a particularly useful form of carbon is a carbon source material that is an organic material that can be carbonized. Such materials can be easily dispersed throughout the silicon carbide compound using as a binder in the initial cold compaction or molding operation, and then decomposed during the sintering operation to remove any necessary excess or bond. Possible carbon can be given. Particularly suitable are organic materials capable of carbonization, such as phenolic resins, acrylic resins and polyphenylene resins. Generally, such carbonizable organic materials provide about 30 to about 50 percent of their initial carbonizable carbon.

In one method for compounding the present invention, the silicon carbide component, the carbon component, and the aluminum nitride component are mixed, preferably by dispersing the carbon source material throughout the silicon carbide and aluminum nitride components, and then the mixture is mixed. Approximately 12,000psi to approximately 18,00psi
The green compact is sintered by cold pressing at a pressure of 0 psi (about 844 to about 1265 kg/cs2).The green compact is then sintered under substantially pressureless sintering conditions. This method is particularly suitable when the composition contains from about 3 to about 45 weight percent of relatively free aluminum nitride. The product finds use in the manufacture of crucibles, refractories or furnace parts.

In the method of the present invention, sintering! 11! The articles contain relatively small amounts of aluminum nitride, usually about 0.5 to about 3.0 weight percent. Such products are produced by intimately mixing silicon carbide and carbon components, cold pressing to form a green compact, and then sintering the green compact in an aluminum nitride atmosphere. suitable for manufacturing. An atmosphere of aluminum nitride can be created during the sintering step by heating the aluminum nitride source to a temperature above its vaporization point.

Products of this type are particularly suitable for use in the production of components for equipment or tools to be used under severe abrasive, high temperature or corrosive conditions.

The starting mixtures of the invention also contain relatively small amounts of materials as sintering aids, such as boron or boron-containing compounds.
It can contain. Sintering aids are generally effective in the range of about 0.3 to about 3.0 weight percent of the aid, such as boron, based on the weight of the silicon carbide component. Adding a boron-containing atmosphere to the furnace during sintering can aid in densification. In such a system, boron gas can be used in the air between the sintered lips,
or a boron source such as H, BO, or B20. may be placed in a furnace and decomposed during the sintering operation. In either system, it is preferred to maintain a partial pressure of boron of at least about 1 ()-'' atmospheres during the sintering operation.

The sintered ceramic products of the present invention are of high density, high strength, substantially non-porous, and are particularly useful in engineering applications. If desired, the dense, high-strength silicon carbide product can be subsequently machined by diamond grinding, electrochemical machining, ultrasonic machining or electrical discharge machining to produce tools or machine parts requiring close tolerances. can be given.

The sintered ceramic articles of the present invention are about 55% aluminum nitride co-sintered with about 0.5 to about 45 weight percent aluminum nitride.
and about 99.5 weight percent silicon carbide. The products of this invention are substantially insoluble in hot water.

The sintered product has a bulk density of at least 75 percent of the theoretical density of silicon carbide. For luxury applications, a density of at least 85 percent of theory is desirable, and densities in excess of 90 percent can be achieved with the mixtures of the present invention.

The silicon carbide starting material is preferably used in finely divided form having a particle size of less than about 5 microns, more preferably less than about 2 microns.The silicon carbide starting material is preferably used in 8.
It has an i1 area exceeding Or+27g and is approximately 20m”
Surface areas greater than 7g are very useful.

The carbon component present in an amount of about 0.5 to about 6.0 weight percent can be used in finely divided form having a particle size of less than about 5 microns, preferably less than about 2.0 microns. However, for example, carbonizable organic material may serve a dual purpose, to act as a binder during the cold Ith process and as a carbon source when carbonizing it subsequently during the sinter process. It is preferable to use a carbonization source material such as θ~. Organic resins that provide residual carbon in an amount of about 30 to about 50 percent by weight after carbonization are particularly useful in this manner.

By thoroughly mixing the silicon carbide starting material and the carbon or carbon source material, a dispersion of the carbon source material throughout the silicon carbide material is achieved.

In one aspect of the invention, the amount of aluminum nitride desired, particularly in the sintered product, is about 30% by weight, based on the total weight of the mixture.
．． From 0 to about 45.0 weight percent, the aluminum nitride component in finely divided form is admixed with the silicon carbide and carbon or carbon source material components. 10
Submicron particle sizes are preferred. Particle sizes less than 5 microns are particularly useful, and for uniform dispersion, about 2
Submicron particle sizes are particularly useful.

In another aspect of the invention, the desired amount of aluminum nitride in the sintered product is between about 0.5 and about 3.5 degrees of the mixture.
( ) weight percent, the aluminum nitride component may be added in gaseous state to the silicon carbide-carbon mixture during sintering. In this method, silicon carbide and carbon or carbon source components are The mixture is mixed, shaped by cold pressing, and then sintered in an atmosphere containing aluminum nitride at about 5.1 (1-' to about 1.10 -3 atmospheres).

An aluminum nitride atmosphere is created by containing solid aluminum nitride in the furnace, which vaporizes during sintering.
It is appropriate to give. Alternatively, the aluminum nitride can be green-sealed in-situ in the furnace during sintering.

The cold pressurization stage is about 12,000 ps to about 18,000 ps.
Suitably, it is carried out in a metal mold at a pressure of from about 844 to about 1'265 kg/cm'. in general,
Approximately 'J 2,500 psi (8°78, 8 kg/
Pressures above am2 and -E are useful. Approximately 18y000
Pressures in excess of psi can also be used; however, only minimal advantageous results are obtained in the final sintered product.

A second pressing of the mixture of the invention results in an increase in the density of the final product. In such a method, the mixture is first cold pressed and ground to a powder (about 40 meshes in size).
After 7 days, pressurize again. Is this method of removing air from powder particles? =, which is believed to be effective in producing a relatively green compact and a relatively high sintered product density. However, double pressurization is not essential to the invention, and the degree of improvement is not large enough to justify double pressurization as a procedure to be used in all cases.

The compressed product, green compact, typically has a density in the range of about 1.74 to about 1.95 g/c, c. The porosity of is typically about 39. : (ranging from about 45.8%).

The sintering step is preferably carried out using a graphite resistance furnace. Temperatures from about 1900° to about 2250°C are very useful. Typically, if temperatures lower than about 1900' are used, the sintering process will not proceed to give the desired sr product.

If temperatures lower than 2250° C. are used, there is a risk of deterioration of the sintered product.

Preferably, the sintering step is carried out in an atmosphere that is inert to the mixture to be sintered. For example, inert gases such as argon, helium and nitrogen can be used. An atmosphere of ammonia may also be used. Approximately 1 (
A vacuum on the order of +-3) degrees can also be used.

In general, the mixtures of the present invention are sintered under the conditions described above to give the desired co-sintered product when using sintering times of about 1% to about 2 hours. The sintering time is sufficient.

The invention is illustrated in more detail by the following examples,
These examples should not be construed as limiting the invention. All parts and percentages are by weight and all temperatures are degrees Celsius unless otherwise indicated.

Example 1 95 parts of silicon carbide in alpha phase with an average particle size of less than 5 microns, 1 part of aluminum nitride, also with an average particle size of less than 5 microns, and a phenolic resin (Barkham Chemical Branch, Reichhold Chemicals, Inc.) A 4 part carbon mixture was prepared by mixing each component in an acetone slurry in a ball mill for 8 hours using a product commercially available as B178 resin by Co., Ltd. The mixture was then dried at room temperature for about 12 hours. The dried mixture was then ground using a dry ball mill and then sieved using an 80 mesh sieve.

The sifted powder is then heated to 15.0 ml using a mold.
Cold pressing at 00 psi (1054, 5 kg/0 m2) resulted in a green compact of diameter %", height %". Next, after drying this molded body at room temperature,
The phenolic resin composition was cured by heating in air at 110° C. for 1 hour.

The green compact was then sintered for 30 minutes in an argon atmosphere in a graphite resistance furnace at 2150°C. The co-sintered product is 1
．． It was observed that it had undergone linear shrinkage of 0.98%.

This product has a porosity of 2.91% and 3,00 B/e
, c, which corresponds to 9:(,30%) of the theoretical density of silicon carbide.

This example is shown as Example 1 in Table 1. Example 2
-10 were carried out in the same manner.

1st Example To-j Bamboo Carbon EiC-,,-3 OtsuC艮,-11,04,095,01,88 21, +1 2. (197,0+,82:(1,
OB, 0 93,0 1,944
2.0 6.0 92,0 1,91
5 1.0 6.0 90. (l
1. ．． 916 +0.0 6. (
184,01,96720,06,074,0+,96 8 10.0 6.0 B4,9
1.989 +,OO,099,01
,8310 pieces 1,0 4,0 95.0
1.95 books Comparative book using beta phase silicon carbide 10.98 2,91 3,00
98. :(06,6716,352,5479,0
09,564,562,8287,! M 12.44 5.79 2,64
82. :(Ill, 95 9.21
2.5H80,8410,! +8:1.4
7 2.88 90,8010.15
4,53 2,87 89.
5011, +1 4.37 2,87
89.500.89 27.80
2.2:3 69.568.98
5.232.89 90.16 Example 2 Carbon 4.0 using a 3-1'78 phenolic resin composition and 96.0 parts of alpha phase silicon carbide having an average particle size of less than 5 microns. Part () mixtures were prepared by mixing the silicon carbide and resin components as a slurry in acetone in a ball mill for 8 hours. After drying the mixture at room temperature, it was processed as in Example 1 to obtain green moldings.

This green compact was placed in a sintering furnace together with aluminum nitride pellets. Argon world [downstream, 1950℃
The sintering temperature was maintained for 30 minutes. The partial pressure of aluminum nitride was calculated to be approximately 5.10''5 atm. The sintered product has a porosity of 4.25% and a bulk density of 2.621 H/c, c, which is 81.62% of the theoretical density of silicon carbide.
corresponds to

Example 11 is designated as Example 11 in the tJIJ2 table. Examples 12 to 16 also achieved tr in the same manner.

2nd Table II O,04,096,OL82
11.84] 2 1.0 4.0
95.0+, 84 13.38+
3, 1.0 6,0 9:1.0
1,92 1122+4***
1,0 4.0 95.0 1,9
0 10.7415*This car 1.0 8,0
9:(,01,949,7816 books this books 1.(
14,095,0+, 78 17.51 books
He won the championship twice.

83B Oi was added to the furnace atmosphere of the Honzero car.

4.25 2.62 81,623.
24 2,86 82.9B8.9]
2,55 79,
473.10 2.90 90.59
3.77 2,94 91.593.
55 2.80 89+7 This invention should not be considered limited to the specific examples and embodiments described above, and those skilled in the art will appreciate that various modifications can be made without departing from the spirit and scope of the invention. It is important to understand that making changes ends with f.

Claims (1)

[Claims] 1. (a) forming a mixture of finely ground silicon carbide, aluminum nitride, and carbon or a carbon source material; (b) forming a green compact by cold-compressing the mixture; (c) sintering the green compact under substantially pressureless conditions in an inert atmosphere at a temperature of about 1900° to 2250°C; and (d) nitriding from 0.5 to 43 weight percent. Co-sintered silicon carbide-aluminum nitride characterized by recovering a ceramic product consisting of 55 to 97 weight percent silicon carbide co-sintered with aluminum and greater than 2 weight percent and less than or equal to 6 weight percent carbon. How the product is manufactured. 2. (a) preparing a mixture of finely ground silicon carbide, aluminum nitride and carbon or a carbon source material; (b) forming a green compact by cold pressing the mixture; (c) forming a green compact by cold pressing the mixture; The green compact is sintered at a temperature of about 1900° to 2250°C in an inert atmosphere under substantially pressureless conditions, and (d) co-sintered with 0.5 to 43 weight percent aluminum nitride. 1. A method for producing a co-sintered silicon carbide-aluminum nitride product, comprising: recovering a ceramic product comprising from 55 to 97 weight percent silicon carbide and greater than 3 weight percent and less than or equal to 6 weight percent carbon. 3. (a) preparing a mixture of finely ground silicon carbide, aluminum nitride and carbon or a carbon source material; (b) forming a green compact by cold pressing the mixture; (c) forming a green compact by cold pressing the mixture; The green compact is sintered at a temperature of about 1900° to 2250°C in an inert atmosphere under substantially pressureless conditions, and (d) co-sintered with 0.5 to 43 weight percent aluminum nitride. 55 to 97 weight percent silicon carbide and no more than 0.5 to 6 weight percent carbon, with the addition of aluminum nitride in an amount equivalent to 0.3 to 3 weight percent free aluminum. A method for producing a co-sintered silicon carbide-aluminum nitride product, except in the case where: 4. The method according to any one of claims 1 to 3, wherein the particle size of silicon carbide, aluminum nitride, and carbon components is less than 5 microns. 5. The method according to any one of claims 1 to 3, wherein the carbon component is in the form of a carbonizable organic material. 6. The method according to any one of claims 1 to 3, wherein the carbonizable organic material is a phenolic resin. 7. The cold compression stage is about 12,000 to about 18,000 p.
4. The method according to claim 1, wherein the method is carried out at a pressure of si (about 844 to about 1265 kg/cm^2). 8. 0.3 to 5 of the silicon carbide component to the initial mixture
．． 4. A method according to claim 1, wherein a sintering aid consisting of boron or boron source material is added in an amount of 0% by weight. 9. A method according to any one of claims 1 to 3, wherein the atmosphere during sintering contains at least about 10-7 atmospheres of boron. 10. (a) preparing a mixture of finely ground silicon carbide and a carbon source material; (b) cold-pressing the mixture to form a green compact; and (c) forming the green compact. Approximately 5.1 under substantially no pressure conditions
Approximately 1900° to 225° in an inert atmosphere containing aluminum nitride at 0^-^5 to 1.10^-^3 atm.
sintered at a temperature of 0°C, and (d) 0.5-43
55% by weight co-sintered with aluminum nitride
A co-sintered silicon carbide-aluminum nitride product characterized by recovering a sintered silicon carbide-aluminum nitride product comprising ~97 weight percent silicon carbide and greater than 2 weight percent but no more than 6 weight percent carbon. manufacturing method. 11. The method according to claim 10, wherein the particle size of the silicon carbide and carbon components is less than 5 microns. 12. The method of claim 10, wherein the carbon component is in the form of a carbonizable organic material. 13. The method according to claim 10, wherein the carbonizable organic material is a phenolic resin. 14. The cold compression stage is about 12,000 to about 18,000
15. The method of claim 10 carried out at a pressure of from about 844 to about 1265 kg/cm2. 10. The method of claim 10, wherein a sintering aid comprising boron or a boron source material is added. 16. The method of claim 10, wherein the atmosphere during sintering contains at least about 10-7 atmospheres of boron. The method according to scope item 10.