JP2605339B2 - Manufacturing method of composite material heat resistant ceramic article - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a composite material heat-resistant ceramic article provided with a coating derived from an immersion method at a predetermined position.

(Prior Art) In general, ceramics called composite ceramics are formed by mixing powders of different materials at the time of preparation and then firing to form a ceramic body. Such materials are, for example, currently commercially available (h-BN)
-(Si ₃ N ₄ ) composite ceramics are available.

However, these conventional composite ceramics are simply a mixture of starting materials of different materials, and are a kind of mixture. The material properties of the obtained composite ceramics and the intermediate properties of each material used It just shows.

To exemplify the literature about them, Si ₃ N ₄ 52-3649 JP-B for system, JP-B-58-15463 and JP-5
No. 7-38378, etc.
Nos. -195058, 60-195059, 60-195060, and 61-21977.

Thus, the idea of "compositing" was to start from a powder mixture.

By the way, in recent years, materials having higher functions have been demanded, and so many new materials having excellent functions have been demanded, so-called new ceramics. In order to meet such demands, various types of non-oxide powders having high performance have been developed, and a film forming, which is a kind of surface treatment, has been performed on ceramic bulks in order to impart higher functions. . For example, formation of nitride and carbide on a ceramic surface.

In the report of the 26th Ceramic Industry Basic Discussion (January 20, 1988), "Nitride and carbide formation on ceramics by melt immersion method", the formation of nitride and carbide coatings on ceramic bulk objects by the so-called immersion method It has been proposed. However, this is merely an indication that a film has been formed, and the effect of the film on the characteristics of the ceramic substrate and the like have not been clarified. Moreover, what is described in this report is the formation of a coating on the ceramic bulk, which must be processed and formed into articles of a predetermined shape again by means of processing, sintering, and the like.
In terms of the material, no completely different operation and effect can be obtained as compared with the case of the ceramic article molded starting from the above-mentioned mixture.

(Problems to be Solved by the Invention) Accordingly, an object of the present invention is to provide a method for manufacturing a composite material ceramic article in which only the material of necessary parts is arbitrarily changed.

More specifically, an object of the present invention is to provide a method for producing a composite ceramic article in which hexagonal boron nitride is provided as a surface coating on a part of a molded article made of a ceramic substrate, for example, a silicon nitride substrate.

(Means for Solving the Problems) The inventors of the present invention have been conducting various studies on the composite of the ceramic substrate, and found that the coating derived from the immersion method does not deteriorate the characteristics of the ceramic substrate at all.
Rather, they have found that heat resistance, strength, and erosion resistance during welding are significantly improved, and have completed the present invention.

Here, the present invention provides an immersion bath comprising a fluoride-containing molten halide bath containing a target metal,
Next, the article obtained by shaping the ceramic substrate to be treated is immersed in the immersion bath for an appropriate period of time, and the target metal derived from the immersion method provided at a predetermined position on the outer surface of the ceramic substrate. And a coating made of at least one of carbides, borides, nitrides, and silicides.

(Operation) Next, the present invention will be described more specifically.

The molten chloride bath as a representative of the molten salt bath constituting the immersion bath used in the present invention is generally KCl-BaC
The l ₂ as a base composition, fluoride which is obtained by adding, for example, NaF. Other examples of the molten chloride bath include NaCl, LiCl, CaCl _{2 and the} like, and examples of the fluoride include NaF, KF, LiF, CaF ₂ and BaF ₂ . Preferably, a bath composition composed of alkali metal chloride-alkaline earth metal chloride-alkali metal fluoride is preferred. The specific composition ratio and the like at that time are already clear to those skilled in the art from the above description. Generally, KCl-BaCl ₂ -Na
For F-based, KCl 5 to 95 mol%, BaCl ₂ 5 to 95 mol%, and NaF is 5 to 50 mol%. If the fluoride content exceeds 50 mol%, not only the bath temperature becomes too high, but also corrosion problems occur.

Although the kind of the target metal is not particularly limited, one of the objects of the present invention is to form a composite structure, and therefore, a hard metal which has conventionally been considered difficult to form a film, such as S
i, Cr, V, B, W, Mo, Ti, Zr, Hf, Nb, Ta and the like periodic table metals of Groups IVa, Va and VIa are preferred.

Such a target metal is partly added as a compound, typically as an oxide, to the molten chloride bath, but it is easily available and generally easy to handle. Is advantageous. Another part is added as a metal powder. This may be added as a single metal of the target metal or an alloy containing the same, such as a ferroalloy, which is also an advantage of the present invention.

As described above, when sodium metal fluoride is used as the fluoride, the NaF in the molten salt reacts with the oxide to partially generate potassium fluoride, soda, and the like. And they are, for example, TiO ₂ → NaK ₂ TiF ₆ , Cr
₂ O ₃ → NaCrF ₃ , V ₂ O ₅ → Na ₃ VF ₆ , B ₂ O ₃ → KBF ₄ , WO ₃ → K ₃ WF ₆
It is. Then, they react on the surface of the ceramic article to be treated, and are Ti-C (TiC) and Cr-C, respectively.
_{(Cr 7 C 3, Cr 3} C 2, Cr 23 C 6), VC (V 2 C, V 4 C 3, V 8 C 7, VC
_0.88 ), _BC and WC. The single metal or alloy at this time is considered to act as a reducing agent for the metal added as an oxide.

As a modified example, in the molten salt bath, instead of the chloride, an oxide, an iodide or a fluoride may be used, and even in such a case, an alkali metal is used as the oxide, the iodide or the fluoride. And alkoxides, iodides or fluorides of alkaline earth metals.

There is no limitation on the amount of the target metal element or alloy, but 2% by weight of the metal oxide in the immersion bath is sufficient. If the amount is too small, a film having a sufficient thickness cannot be obtained. The practical lower limit is about 1%. On the other hand, if the amount is too large, the thickness of the coating such as the carbide layer becomes uneven. Practically, up to about 7% by weight is acceptable. Preferably it is 5 to 7% by weight.

In the case of the target metal halide, it is contained up to 40%, but if it exceeds that, the problem of corrosion of equipment such as equipment, the generation of halogen gas increases, and the problem of hygiene also occurs .

When an oxide of a target metal is used, a reducing agent for reducing the oxide is added. As a reducing agent,
Mn, Al, Ca, Si, Ti, Zr and the like, or alloys thereof, for example, Fe-Mn, Fe-Al, Fe-Ti, Fe-Zr, Fe-Si, Ca-S
i, Ca-Si-Mn or the like having a higher affinity for oxygen than chromium or Group Va element is used. The mixing ratio of these reducing agents in the treatment bath is suitably about 2 to 20% by weight. If it is less than 2% by weight, the reducing effect is insufficient, and if it exceeds 20% by weight, the formation of carbides is rather hindered. Preferably it is 5 to 15% by weight.

Immersion time in the immersion method according to the present invention, the temperature is different depending on the type of the target product metal compound,
Generally, treatment at 700 to 1100 ° C. for 1 to several tens hours is sufficient.

Meanwhile, as the ceramic substrate used in the present invention is not particularly _{limited, Si 3 N 4, SiC,} h-BN, non-oxide ceramics represented by the carbon material or the like are preferable.

These are made into a composite structure by an immersion method as an article previously formed in a target shape.

That is, ceramic bulk such as Si ₃ N ₄ is sufficiently kneaded according to a conventional method, and the kneaded powder is filled in a cylinder, a cylindrical body, or a mold of a complicated shape body, and pressed under an adjusted atmosphere, and fired. I do. As such a molding means, HI
P (hot isostatic compression method) may be used. After molding, the obtained article is immersed in the immersion bath described in detail so far, and a coating made of at least one of carbide, boride, nitride, and silicide of the target metal is formed at a predetermined position to form a composite material. It is.

As a method of providing the above-mentioned surface coating only at a predetermined position, the following method can be used.

(1) A part other than the predetermined part is, for example, a metal colloid,
Or dipped or bathed in a bath composed of a metal alcohol (eg, ethyl silicate and colloidal silica), dried and fired.

The article made of the ceramic substrate prepared in this way is immersed in the above-described immersion bath to achieve a composite material.

(2) A solution containing an oxide of the target metal is applied to a portion other than a predetermined portion of the article by spraying or the like, and dried.

(3) When the article is in the shape of a container and it is desired to perform compounding only on the inside thereof, the above-mentioned immersion bath is formed inside the compound, and the inner wall portion is formed. Even if the article shape is not a container shape, if it can be formed into a container shape by using a jig as appropriate, it is possible to achieve compounding by this method.

(4) Apply oils and fats such as petrolatum and glycerin to a portion other than the predetermined portion of the article, and then immerse the article in the immersion bath.

Needless to say, when a coating layer is provided on the entire surface of the ceramic substrate article to form a composite, the above-described partial passivation treatment is not necessary, and the entire article may be immersed.

Representative examples of articles made of a ceramic substrate in the present invention are used in high heat fields such as a ring for casting molten metal, a nozzle for casting, a nozzle for metal spatter welding, a crucible for melting metal, a thermocouple protection tube, and a level meter. It is a high temperature member. A predetermined portion of these articles, that is, a portion that comes into contact with a high-temperature material such as a molten metal is compounded by the present invention. For example, in metal sputter welding nozzles, conventionally, the life of a Si ₃ N ₄ ceramic nozzle has been shortened by the adhesion of sputtered metal, but h-BN ceramics to which sputtered metal is less likely to adhere do not have the working strength. Had not been used. However, by forming the h-BN only inside the Si ₃ N ₄ ceramic nozzle where sputtered metal adheres according to the present invention, the strength of the conventional Si ₂ N ₄ A nozzle for metal sputter welding has been developed that has the same strength as a ceramic nozzle but has low erosion due to the adhesion of sputtered metal. Similarly, in the thermocouple protection tube, ring, and nozzle for casting, Si
By compounding ₃ N ₄ ceramic into Si ₃ N ₄ -hBN,
Without losing the high strength characteristics of the conventional Si ₃ N ₄ ceramic, only the thermal shock resistance can be improved, and the life can be extended.

However, the Si ₃ N ₄ -hBN composite ceramic obtained by the existing mixing method loses the high strength of the Si ₃ N ₄ ceramic and frequently breaks during use.

On the other hand, Si ₃ N ₄ ceramic and Si ₃ N ₄ − (T
i—N), Si ₃ N ₄ — (Zr—N), and SiC— (Ti—C) ceramics are compounded by internal Si ₃ N ₄ and surface layers Ti—N, Zr—
N, the compressive stress generated on the surface due to the difference in thermal expansion from the Ti-C composition, the strength is improved, for example, when used for casting thermocouple protection tube, ring, nozzle, etc., the life of those articles become longer. In addition, for applications such as rolls, packings, casting nozzles, rings, and crucibles for melting metals, use of crucibles for melting metals requires only oxidation resistance and wear resistance, and only h-BN and C materials H-BN- (Ti
-N), h-BN- (Zr-N), C- (Ti-C), C-
Oxidation resistance and strength are improved by changing the composite ceramic to (Cr-C), etc., and the low oxidation resistance and abrasion resistance, which were the drawbacks of conventional h-BN and C materials, were overcome. I can make it. This can extend the life of an article such as a metal melting crucible.

As described above, the composite article according to the present invention is particularly suitable for the above-mentioned applications because of its remarkable improvements in heat resistance, erosion resistance during welding and high-temperature strength.

It is not necessary to perform a preliminary treatment on the molded article prior to the immersion treatment, but preferably, a treatment such as degreasing can further enhance the film adhesion and the like.

Incidentally, the film formation by the immersion method according to the present invention may be performed on a ceramic molded article previously coated with a metal by CVD or vacuum sputtering as appropriate, and in such a case, such a metal coating is used as the ceramic substrate. Any material may be used as long as possible, and in some cases, an oxide-based ceramic may be used.

However, the film provided in advance in this way is not limited to the metal coating, and the same applies to the metal compound coating according to the present invention described above. That is, on the surface of the molded article on which the metal layer or the metal carbide layer is formed in this manner, the target metal in this case is preferably B by a treatment using a similar molten salt bath again.
By using a boron oxide such as B ₂ O _3, the metal of the metal carbide already formed on the surface of the molded article may then be combined with boron to form a metal boride. That is, a boron compound (eg, boron oxide) is converted into, for example, B ₂ O ₃ → KBF _{4 in a} fluoride-containing molten salt bath, and this is combined with, for example, Ti in the surface coating of the molded article to form TiB ₂ or TiB.
b, that is, MB ₂ or MB (M: metal) is produced.
According to this treatment, the characteristics of the ceramic article as a composite material are further improved.

Next, the present invention will be described more specifically based on examples. In this specification, “%” is “% by weight” unless otherwise specified.

Example 1 KCl, BaCl ₂ and NaF were added to a porcelain crucible in 42.2 and 22.2, respectively.
After adding 0.2 and 37.6 mol% and heating and melting the whole to 89.3 g, 5 g of Ti, Zr, B metal oxide and 25 g of metal or alloy powder (ferroalloy) of the metal are added, and the mixture is sufficiently stirred, and then immersed in an immersion bath. did.

A sample rod made of a Si ₃ N ₄ ceramic substrate having a size of 3 × 4 × 40 mm by a conventional sintering method was immersed in the immersion bath thus prepared. The immersion conditions were 1100 ° C. for 10 to 20 hours. Each of the Si ₃ N ₄ substrate surfaces has a thickness of about 100 to 200 μm T
The i-N, Zr-N, and BN layers were formed to make a composite material.

Examination of the characteristics of the above-mentioned sample rod revealed a remarkable improvement in strength and thermal shock resistance (see Table 2).

Crucibles and nozzles of the same material were molded by the same sintering method in place of the sample rod of the Si ₃ N ₄ base, and the same processing was performed on the obtained molded body. Only the inner wall
The outer wall is immersed in an aqueous solution of ethyl silicate: colloidal silica = 1: 1 to form a composite structure of Ti—N, Zr—N, and BN, dried, baked at 500 ° C. for 10 minutes, and dipped. Was done. Similar results were obtained in each case. The service life of casting nozzles, rings, and thermocouple protection tubes was extended about twice as compared with the untreated ones. In particular, the No. 3 inner wall BN composite Si ₃ N ₄ ceramic nozzle is hard to wet with sputtered metal when used as a metal welding nozzle, so spattered metal is less likely to adhere and the service life is about 5 times longer. Extended.

Example 2 In this example, the same molten salt bath as in Example 1 was used, and 25 g and 5 g of Ti metal and TiO ₂ were added, respectively, and sufficiently stirred to form an immersion bath. A sample rod as a SiC ceramic substrate article having a size of 3 × 4 × 40 mm formed by a conventional sintering method was immersed in the immersion bath thus prepared. Immersion conditions are 1050 ° C,
5 hours.

A Ti—C layer having a thickness of 100 to 150 μm was formed on the surface of the SiC substrate to form a composite structure.

When the characteristics of the sample rod were examined, remarkable improvements in strength and thermal shock resistance were found (see Table 4).

Example 3 In this example, the same molten salt bath as in Example 1 was used, and 25 g and 5 g of Ti, Zr metal and TiO ₂ and ZrO ₂ were added, respectively, and sufficiently stirred to form an immersion bath. The thus-prepared immersion bath was immersed in a 3 × 4 × 40 (mm) dimension h-BN-based substrate sample rod formed by a conventional method. The immersion conditions were 950 ° C. for 5 hours. The results are shown in Table 5, where the surface of h-BN was Ti
The -N and Zr-N layers were formed to a thickness of 10 to 30 µm to form a composite structure.

Examination of the characteristics of the above samples revealed that the hardness and oxidation resistance were significantly improved (Table 6).

The same processing was performed on an article obtained by molding a casting ring, a casting nozzle, and a crucible from the same material by a sintering method instead of the h-BN substrate sample rod. When the article to be treated was formed into a container shape using a jig, only the inner wall portion in contact with the high-temperature molten metal was left as it was, and only the outer wall portion that was easily oxidized was formed into a composite structure according to the present invention. The same result as in Example 1 was obtained. Obtained.

Example 4 In this example, the same molten salt bath as in Example 1 was used, and after heating and melting, 5 g of each predetermined metal oxide and 25 g of a metal or alloy alloy (ferroalloy) of the metal were added and sufficiently stirred. Then, a immersion bath was used.

A sample rod made of a carbon substrate having a size of 3 × 4 × 40 (mm) formed by a conventional sintering method was immersed in the immersion bath thus prepared. The immersion conditions were 950 ° C. for 2 hours.

The results are summarized in Table 7. As shown in Table 7, a carbide layer of each target metal was formed to a thickness of about 5 to 20 µm on the surface of the carbon substrate to form a composite structure.

Examination of the characteristics of the sample bar revealed that hardness and oxidation resistance were significantly improved (see Table 8).

A roll of the same material in place of the carbon substrate sample rod,
A packing, a nozzle, and a crucible were formed, and each article was treated in the same manner as in Example 3 to obtain similar results.

Comparative Example 1 In this example, for comparison with the example, the average particle size was 1 μm.
Si ₃ N ₄ and powder having an average particle diameter of 0.1 to 0.5 μm h-BN are mixed at an arbitrary ratio, molded at a molding pressure of 1 t / cm ² , and 1750 in a N ₂ gas atmosphere.
C. (holding for 2 hours) to obtain a 3 × 4 × 40 mm fired product.

Comparative Example 2 The surface of Si ₃ N ₄ powder having an average particle diameter of 1 μm was converted into 0.1 and 0.14 μm h-BN by the dipping method according to Example 1. Using this powder, molding was performed at a molding pressure of 1 t / cm ² , and 1750 ° C. in a N ₂ gas atmosphere.
(Holding for 2 hours) to obtain a fired product having a shape of 3 × 4 × 40 mm.

Table 9 shows the characteristics of the samples of Comparative Examples 1 and 2. Ninth
As is clear from the table, the strength or the thermal shock resistance is remarkably inferior to the composite ceramic article of the present invention.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tetsushi Aoki 418-14, Potterino Nitta, Niikawa-cho, Nishi-Kasugai-gun, Aichi (56) References JP-A-63-147882 (JP, A) JP-A-63-147883 (JP, A)

Claims (4)

(57) [Claims] 1. An immersion bath comprising a fluoride-containing molten halide bath containing a target metal is prepared, and an article obtained by forming a ceramic substrate to be treated is immersed in the immersion bath for an appropriate period of time. Characterized by comprising a ceramic substrate and a coating made of at least one of carbide, boride, nitride, and silicide of a target metal derived from an immersion method provided at a predetermined position on the outer surface of the ceramic substrate. A method for manufacturing composite heat-resistant ceramic articles. 2. The fluoride-containing molten halide bath according to claim 1, wherein
3. The method according to claim 1, wherein the oxide is prepared by adding an oxide of the target metal and a simple metal or alloy. 3. The method according to claim 1, wherein the halide of the fluoride-containing molten halide bath comprises at least one of an alkali metal and an alkaline earth metal halide. 4. The process according to claim 1, wherein the fluoride in the fluoride-containing molten halide bath comprises at least one of alkali metal and alkaline earth metal fluorides. .