JPH0712990B2 - Reaction sintering type silicon nitride bonded sintered body having excellent resistance to molten metal casting and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to improvement of metal melt castability of a reaction-sintered silicon nitride bonded sintered body that is in contact with a metal melt, and A reaction-sintered silicon nitride bonded sintered body in which the surface layer of the sintered body is formed from a material with a molten metal-resistant cast material made of boron nitride, aluminum, or a mixture thereof using silicon nitride constituting the sintered body as a binder. And a manufacturing method thereof.

Prior art and its problems Silicon nitride reactive sintered ceramics such as silicon nitride simple substance or a composite of silicon nitride and silicon carbide as a structural material that contacts molten metal such as aluminum, copper, zinc, magnesium, etc. The body is being used.

For example, structural materials for molten aluminum, such as furnace wall materials for melting furnaces and holding furnaces, Stokes for low-pressure casting equipment, gutter materials for pouring molten metal, heater tubes for molten metal immersion, protective tubes for thermocouples for temperature measurement, degassing It is applied in various forms such as a gas blowing pipe and a member for stirring molten metal.

In the case of this type of structural material, if there is reactivity with the molten metal that contacts in a static or dynamic state, the molten metal will adhere to the structural material and react and corrode, resulting in loss of its function as a structural material. However, as the reaction product becomes unusable and the reaction product peels off or elutes to cause the contamination of the molten metal, it is required to have a metal melt casting resistance as good as possible.

Thus, the silicon nitride body or its composite with silicon carbide is superior to other ceramics and conventional materials in high-temperature strength and thermal shock resistance, and the reaction sintering method, hot pressing, and normal pressure sintering are performed. Those manufactured by various manufacturing methods such as the method have been used. However, with the expansion of its applications, higher levels of required properties are required, and in particular, there is an increasing need for improving metal molten metal casting resistance.

As a countermeasure, a composite of silicon nitride and boron nitride silicon carbide is proposed, for example, in JP-A-56-120575, but it is still at an insufficient level and the cost is high. Has become.

Also, means for spraying and coating boron nitride on the molten metal contact surface, for example, means for forming a coating layer by high temperature lubrication release boron nitride spray has been diverted. However, in this case, since boron nitride is not bonded to the silicon nitride reaction-sintered matrix and is merely adhered, it peels off in a short period of time, and it is necessary to repeatedly apply it, which results in operational control. It was complicated.

Further, by a method of forming an aluminum layer on the surface of a silicon nitride sintered body and then raising the temperature in two steps in a nitrogen gas atmosphere to carry out reaction sintering (for example, JP-A-63-238950), corrosion resistance with less exfoliation. Although a method for forming a surface layer having a certain thickness has been proposed, the manufacturing process is complicated, operation control is difficult, and the joining strength of the formed aluminum nitride is still insufficient. There is also a method of applying a glassy or clayy coating agent, but it is not preferable because there is a problem of molten metal contamination due to elution of the glassy component and the clayy component during use.

The present inventor, as a result of studying in view of these problems, utilized a sintering mechanism in the manufacturing method of the reaction-sintered silicon nitride bonded sintered body, and at least the boron nitride or the nitride on the molten metal contact surface. The inventors have come up with the idea that the metal melt casting resistance can be improved by forming a surface layer in which aluminum is integrated as a sintered body with a silicon nitride binder by reaction sintering, and the first invention is proposed. It was

Further, as a specific method of forming the surface layer, by utilizing the simplicity of the coating method, a green surface layer of a required thickness is formed, and subsequently, nitriding reaction sintering is performed by simultaneous integration of the base and the surface layer, thereby reacting. The inventors have come to the idea of forming the surface layer while suppressing the manufacturing cost of the sintered type silicon nitride bonded sintered body, and have come to propose the second and third inventions.

According to a first aspect of the present invention, a surface layer of a reaction-sintered silicon nitride-bonded sintered body in contact with a molten metal has boron nitride or aluminum nitride or a mixture thereof using silicon nitride of the sintered body as a binder. A metal-resistant molten metal casting material comprising a body, wherein the metal-resistant molten metal casting material and the sintered body are integrated by the silicon nitride of the sintered body. The present invention proposes a reaction-sintered silicon nitride-bonded sintered body having excellent sticking property.

Here, the reaction-sintered silicon nitride-bonded sintered body means a reaction-sintered silicon nitride simple substance or a reaction-sintered silicon nitride bond in which 1 to 90% by weight of silicon carbide is mixed. It is composed of a quality complex.

Further, a second invention of the present application is to provide a metal-metal-resistant cast material made of boron nitride, aluminum nitride, or a mixture thereof on a molten metal contact surface of a metal silicon preform in a weight ratio to metal silicon (95: 5) to (1 to 99) after coating with a coating agent prepared by dispersing in a mixing ratio, and then in a nitrogen gas atmosphere 11
A method for producing a reaction-sintered silicon nitride bonded sintered body having excellent resistance to molten metal casting, which is characterized by performing reactive sintering at 00 to 1800 ° C.

Further, the third invention of the present application is such that the molten metal contact surface of the metal silicon preform is coated with a base treating agent in which metal silicon is dispersed, followed by boron nitride or aluminum nitride or a mixture thereof. After coating with a coating agent made by dispersing a metal-resistant molten metal casting material with metal silicon in a weight ratio of (95: 5) to (1:99), the temperature is raised to 1100 to 1800 ° C in a nitrogen gas atmosphere. A method for producing a reaction-sintered silicon nitride bonded sintered body having excellent resistance to molten metal casting, which is characterized in that reaction sintering is performed.

The term "metal silicon preform" as used herein means 3 to 20 parts by weight of water based on 100 parts by weight of a metal silicon mixture consisting of metal silicon alone or metal silicon mixed with 1 to 90% by weight of silicon carbide. Parts by weight, preferably 5 to 15 parts by weight, and 0.05 to 5 parts by weight, preferably 0.5, of an organic binder such as methylcellulose, polyvinyl alcohol, polyacrylic acid ester, etc.
3 to 3 parts by weight are blended, kneaded with a mixer or the like, and subsequently molded into a desired shape. In that case, depending on the desired final shape, extrusion molding method, die pressing method, vibration molding method,
Appropriate forming means such as slurry casting method and rubber pressing method can be applied. For example, the method disclosed in JP-A-62-132606 can be applied. In this case, it is desirable that the silicon metal and silicon carbide have a purity of 99% by weight or more and a particle size of 0.1 μm to 10 mm.

Subsequently, the molded body is subjected to room temperature curing, and then cured and dried at 100 to 250 ° C. for 1 to 50 hours to remove moisture and complete curing of the organic binder to have sufficient shape retention strength, and thus, it is a preformed body. It

Then, the surface of the metal silicon preform is coated with a coating agent directly or through a surface treatment agent in a layer thickness of 10 μm to 1 mm.

Here, the coating agent is a mixture of boron nitride and aluminum nitride in a weight ratio, or a mixture thereof (2: 3 to
(3: 2 mixing ratio) and metal silicon are in a weight ratio of (95: 5) to (1:99), more preferably (70:30) to (20: 8).
Water or non-oxidizing organic solvent such as ethanol, butanol, and hexane is added to 50 parts by weight, preferably 80 to 150 parts by weight, relative to 100 parts by weight of the compounded in the mixing ratio of 0).
If desired, an organic binder similar to the above may be added in an amount of 10 to 30.
1 to 5 parts by weight, preferably 15 to 20 parts by weight, or 1 to 5 parts by weight, preferably 2 to 4 parts by weight of a dispersant such as oleic acid, an acrylic copolymer or a polycarboxylic acid type surfactant. -It is prepared by stirring.

In this case, boron nitride and aluminum nitride are
It is preferable that it has a purity of 98% by weight or more and is finer than the silicon nitride matrix, and the average grain size is 30 μm.
The following is preferably 0.1 to 5 μm. Further, in the case of boron nitride, boron oxide as an impurity vitrifies during reaction sintering and impedes the gas permeability of nitrogen gas to the center, so use a boron oxide content of 0.1% by weight or less. Is preferred.

Further, the metal silicon used in this case may be the same as the metal silicon used for the preformed body, but finer particles are preferable, and the average particle size is 30 μm or less, preferably 0.
It is preferably 1 to 5 μm.

The surface treatment agent is 50 to 200 parts by weight, preferably 80 to 150 parts by weight of water or a non-oxidizing organic solvent such as ethanol, butanol, and hexane, with respect to 100 parts by weight of metal silicon, and further, if desired. 10 to 30 parts by weight, preferably 15 to 20 parts by weight, the same as the organic binder used in the production of the preformed body,
Alternatively, it is prepared by mixing and stirring 1 part by weight or less of a dispersant such as oleic acid, an acrylic copolymer, and a polycarboxylic acid type surfactant, and is coated with a layer thickness of 10 μm to 500 μm. . The metal silicon used for the base treatment agent may have the same properties as those used for the coating agent.

As a means for coating the preform with the coating agent and the base treatment agent, brush coating, spray application, dobbing application, or the like is appropriately applied according to the shape characteristics of the preform. After coating, drying or curing drying is performed at 100 to 250 ° C. to fix as a surface layer. Therefore, in the case of interposing the underlying layer, the drying or curing drying is repeated at each step of coating with the undercoating agent and the coating agent.

The preformed body on which the dried surface layer is formed is subsequently carried into a nitriding reaction sintering furnace, and is 1100 to 1800 ° C under a nitrogen gas atmosphere of about 0.05 to 0.8 atm, more preferably 1300 to 1500 ° C at 50 ° C.
Sinter for 100 hours for nitriding reaction.

As a result, silicon metal is simultaneously converted to silicon nitride from the surface layer to the center of the preform body. At that time, nitrogen molecules are bonded to the metal silicon powder in the surface layer, and the porosity in the surface layer portion is reduced, so that boron nitride and aluminum nitride in the surface layer are hardened and the binder silicon nitride produced is formed. Since the element is integrated with the reaction-sintered silicon nitride bonded sintered matrix, the surface layer formed is firmly integrated with the reaction-sintered silicon nitride bonded sintered matrix.

Example 50 A metal silicon having a purity of 99.9% by weight and a particle size of 10 μm under is used.
50 parts by weight of silicon carbide having a purity of 99.8% by weight and a particle size of 10 μm under and 3 parts by weight of an aqueous solution of polyvinyl alcohol having a concentration of 10% by weight are kneaded with a kneader, and the inner diameter is 500 mmφ.
With a cylindrical rubber mold with a length of 500 mm, 1000 kg /
After isostatic pressing (CIP) under a cold isostatic pressure of cm ² , the mold was removed, and the mixture was aged at room temperature for 5 hours and then dried in a drying oven at 150 ° C for 1 hour.
A preform was produced by drying and curing for 0 hours.

On the other hand, the coating agent was boron nitride and aluminum nitride with a particle size of 10 μm each and a purity of 98% by weight, and a particle size of 10 μm.
It was prepared by adding 120 parts by weight of water to 100 parts by weight of a mixture of the undermetal silicon and the mixture at the ratio shown below and stirring the mixture. Also, as a surface treatment agent, 100 parts by weight of metal silicon having a particle size of 10 μm and water 150
Part by weight was mixed and stirred to prepare.

A brush was applied to the entire outer surface of the preform with a predetermined film thickness using these coating agents and base treatment agents, and dried to form a surface layer.

Then, it is carried into a reaction sintering furnace in a nitrogen gas atmosphere of 0.5 atm and kept at 1250 ° C for 20 hours and 1400 ° C for 20 hours. 2
Reactive sintering was performed by the stepwise heating method.

After preheating the obtained silicon nitride reaction sintered body to 300 ° C, it was completely immersed in the molten metal held at 730 ° C of JIS standard AC-4C alloy which is an aluminum alloy for casting in a test furnace in an argon gas atmosphere. After immersion, the resistance to metal casting and the resistance to metal contamination were evaluated after a predetermined period.

For comparison, a coating agent and an undercoating agent that do not contain metallic silicon, and those that do not form any surface layer were manufactured, and then subjected to nitriding reaction sintering treatment under the same conditions. The applied product was manufactured and subjected to an evaluation experiment. Separately, 1.8% by weight of commercially available colloidal boron nitride is added to the silicon nitride reaction sintered body produced by subjecting the surface of the metal silicon preform of the same material to the nitriding reaction sintering under the same condition without treatment. A comparative material having a surface layer of boron nitride formed by using a boron nitride spray agent in which 1% by weight of an organic binder was dispersed in a solvent was prepared and subjected to the same evaluation experiment.

The results of these evaluations are shown in the following table.

EFFECTS OF THE INVENTION The present invention provides a metal melt-resistant cast material made of boron nitride, aluminum nitride, or a mixture thereof using silicon nitride of a sintered body obtained by reaction sintering as a binder on the surface layer of the sintered body. Is a reaction-sintered silicon nitride-bonded sintered body formed integrally with the sintered body, and such a sintered body is a molten metal casting material made of boron nitride, aluminum nitride, or a mixture thereof. Since it is manufactured by sintering at the same time as 1), 1) peeling is less likely to occur, there is little contamination of the molten metal, it has excellent resistance to metal melt casting, and it is durable and can be used for a long time.

2) It can be easily obtained in a small number of steps.

The effect that is excellent in practicality such as is exhibited.

Claims (3)

[Claims] 1. A metal-resistant molten metal whose surface layer in contact with the molten metal of a reaction-sintered silicon nitride-bonded sintered body comprises boron nitride, aluminum nitride, or a mixture thereof using silicon nitride of the sintered body as a binder. A reaction excellent in castability against molten metal, characterized in that it is formed from a cast material, and the cast material against molten metal and the sintered body are integrated by silicon nitride of the sintered body. Sintered silicon nitride bonded sintered body. 2. A molten metal-resistant cast material made of boron nitride, aluminum nitride, or a mixture thereof is provided on the molten metal contact surface of the metal silicon preform in a weight ratio of metal silicon to (95: 5) to (1). The reaction mixture is coated with a coating agent that is dispersed at a compounding ratio of 99 to 99), and then is reactively sintered at 1100 to 1800 ° C in a nitrogen gas atmosphere. -Type silicon nitride bonded sintered body manufacturing method. 3. A metal-resistant molten metal casting made of boron nitride, aluminum nitride, or a mixture thereof is coated on a molten metal contact surface of a metal silicon preform with a surface-treating agent in which metal silicon is dispersed. The weight ratio of the material to metal silicon (95
After coating with a coating agent that is dispersed at a compounding ratio of 5 to 5 to 1:99, 1100 to 18 in a nitrogen gas atmosphere.
A method for producing a reaction-sintered silicon nitride-bonded sintered body having excellent resistance to molten metal casting, which comprises performing reaction sintering at 00 ° C.