JPH03223192A - Sintered material bonded with silicon nitride of reaction-sintering type having excellent resistance to welding of metallic melt and its production - Google Patents

Abstract

PURPOSE:To obtain a sintered material bonded with silicon nitride having excellent resistance to welding of metallic melt in a low cost by forming a surface layer comprising BN, AlN or a mixture of the both together with a matrix in one body in applying a silicon nitride obtained from a reaction-sintering to a face of a sintering matrix bonded with the silicon nitride of reaction- sintering type to be brought into contact with a melt as binder. CONSTITUTION:A coating agent in which BN, AlN or a mixture of the both is dispersed in a mixing weight ratio to Si of (95:5) to (1:99) is applied onto a face of a pre-molded material of metallic silicon to be brought into contact with a melt and a resultant material is subjected to a reaction-sintering at 1100-1800 deg.C in N2 gas atmosphere to afford the objective sintered material bonded with a silicon nitride of reaction-sintering type having excellent resistance to welding of metallic melt.

Description

[Detailed Description of the Invention] The present invention relates to improving the resistance to molten metal casting of a reactive sintered silicon nitride bonded sintered body that comes into contact with molten metal. In particular, reactive sintered silicon nitride bonded sintered bodies, in which a surface layer made of boron nitride, aluminum nitride, or a mixture thereof with silicon nitride as a binder is formed directly or through a single layer of silicon nitride; The present invention relates to a manufacturing method thereof.

Silicon nitride reactive sintered ceramics, such as nitride rope car bodies and composites of silicon nitride and silicon carbide, are used as structural materials that come into contact with molten metals, such as aluminum, copper, zinc, and magnesium. body is used.

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

In the case of this type of structural material, if it is reactive with the molten metal that comes into contact with it in a static or dynamic state, the molten metal will adhere to the structural material and cause reaction corrosion, causing it to lose its function as a structural material. However, it becomes unusable, and the reaction products peel off or elute, causing contamination of the molten metal. Therefore, it is necessary to have as good a resistance to molten metal casting as possible.

Therefore, silicon nitride bodies or their composites with silicon carbide have superior high-temperature strength and thermal shock resistance compared to other ceramics and conventional materials, and are suitable for reaction sintering, hot pressing, and pressureless sintering. Products manufactured by various manufacturing methods such as the method have been used. However, as its uses expand, higher levels of required properties are required, and in particular, there is a growing need to improve its resistance to molten metal casting.

As a countermeasure to this problem, a composite material in which boron nitride silicon carbide is blended with silicon nitride has been proposed, for example in Japanese Patent Application Laid-Open No. 56120575, but it is still at an insufficient level and the cost is relatively high. There is.

In addition, a method of spraying or applying boron nitride on the molten metal contact surface, for example, a method of forming a coating layer using a boron nitride spray for high-temperature lubricated mold release, has also been used.

However, in this case, boron nitride is not bonded to the silicon nitride reaction sintered matrix and is merely attached to it.
It peels off in a short period of time and requires repeated application, making operational management complicated.

Furthermore, there is a method in which an aluminum layer is formed on the surface of a silicon nitride sintered body, and then the temperature is raised in two steps in a nitrogen gas atmosphere to perform reaction sintering (for example, Japanese Patent Application Laid-Open No. 63238950).
A method of forming a corrosion-resistant surface layer with less peeling has been proposed, but the manufacturing process is complicated and operation management is difficult, and the bonding strength of the aluminum nitride formed is still not sufficient. There is also a method of applying a vitreous or clayey coating agent, but this is not preferred because it poses the problem of molten metal contamination due to elution of glassy or clayey components during use.

As a result of consideration in view of these problems, the present inventors utilized the sintering mechanism in the production method of reaction-sintered silicon nitride bonded sintered bodies to inject boron nitride or nitride into at least the molten metal contact surface. We came up with the idea that the resistance to molten metal casting can be improved by forming a surface layer where aluminum is integrated with the base material using a silicon nitride binder by reactive sintering, and came to propose the first invention.

In addition, as a specific method for forming the surface layer, a green surface layer of the required thickness is formed by taking advantage of the simplicity of the coating method, and then a nitriding reaction and sintering is caused by simultaneous integration of the matrix and the surface layer. We came up with the idea of forming a surface layer while suppressing the manufacturing cost of a sintered silicon nitride bonded sintered body, and came to propose the second and third inventions.

The first invention of the present application is to provide a surface layer made of boron nitride or aluminum nitride or a mixture thereof with silicon nitride as a binder on the molten metal contact surface of a reactive sintered silicon nitride bonded sintered matrix. The present invention proposes a reactive sintered silicon nitride bonded sintered body which is formed directly or via a silicon nitride layer and has excellent molten metal casting resistance.

Here, the reaction sintered silicon nitride bonded sintered matrix refers to a reaction sintered nitride rope car body or a reaction sintered silicon nitride bonded body mixed with 1 to 90% by weight of silicon carbide. An award consisting of a complex.

Further, the second invention of the present application is to apply boron nitride, aluminum nitride, or a mixture thereof to silicon metal at a weight ratio of (95:5) to (1:99) on the molten metal contact surface of the metal silicon element molded body.
) Reactive sintering type nitriding with excellent molten metal casting resistance characterized by coating with a coating agent dispersed at a blending ratio of This is a method for producing a silicon-bonded sintered body.

Furthermore, the third invention of the present application is to apply boron nitride, aluminum nitride, or a mixture thereof to the molten contact surface of the metal silicon element molded body, after coating the molten contact surface with a base treatment agent containing metal silicon dispersed therein. The weight ratio of (95:5) to (
After coating with a coating agent dispersed at a blending ratio of 1:99), a coating agent of 1100 to 1800
This is a method for producing a reactive sintered silicon nitride bonded sintered body having excellent resistance to molten metal casting, characterized in that reaction sintering is carried out at a temperature of .degree.

Here, the metal silicon element molded body refers to a metal silicon cable body or a metal silicon mixture consisting of a mixture of 1 to 90% by weight of silicon carbide to 100 parts by weight of water to 3 to 3 parts by weight of water.
20 parts by weight, preferably 5 to 15 parts by weight, and 0.05 to 5 parts by weight, preferably 0.5 to 3 parts by weight of an organic binder such as methylcellulose, polyvinyl alcohol, polyacrylic ester, etc. The mixture is kneaded using a mixer and then molded into a desired shape. In that case, appropriate shaping methods such as extrusion molding, mold pressing, vibration molding, slurry casting, rubber pressing, etc. can be applied depending on the desired final shape. For example, JP-A-62-1326
The method disclosed in Publication No. 06 and the like is also applicable. In this case, it is desirable that the metal silicon and silicon carbide have a purity of 99% by weight or more and a particle size of 0.1 μm to 10 nm.

Subsequently, the molded body was cured at room temperature and then heated at 100 to 250°C.
Cured and dried for ~50 hours to remove moisture and complete hardening of the organic binder to provide sufficient shape-retaining strength.
It is considered to be a preformed body.

Next, a coating agent is coated on the surface of the metal silicon element molded body directly or via a surface treatment agent to a layer thickness of 10 μm to 1 μm.

Here, the coating agent is boron nitride and aluminum nitride alone or a mixture of each (2:3) by weight.
~3:2 mixing ratio) and metallic silicon in a weight ratio of (95:5) to (1:99), more preferably (70:30).
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, hexane, etc., per 100 parts by weight of the mixture at a blending ratio of 20 to 80. , and if desired, 10 to 30 parts by weight, preferably 1 part by weight of the same organic binder as above.
5 to 20 parts by weight, or 1 part of a dispersant such as oleic acid, acrylic copolymer, polycarboxylic acid type surfactant, etc.
It is prepared by mixing and stirring ~5 parts by weight, preferably 2 to 4 parts by weight.

In this case, boron nitride and aluminum nitride each have a purity of 98% by weight or more, and preferably have finer particles than the silicon nitride matrix, with an average particle size of 30% by weight or more.
．． It is desirable that the thickness is 1Jm or less, preferably 0°1 to 5 μm. Furthermore, in the case of boron nitride, boron oxide as an impurity vitrifies during reaction sintering and inhibits the permeability of nitrogen gas to the center. It is preferable to use one with a content of 1% by weight or less.

Further, the metal silicon used in this case may be the same as the metal silicon used for the preform, but it is preferable to use finer particles, with an average particle size of 30 μm or less, preferably 0.1 to 0.1 μm. A thickness of 5 μm is preferable.

The surface treatment agent contains 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, hexane, etc., based on 100 parts by weight of metal silicon, and further as desired. 10 to 30 parts by weight, preferably 15 to 20 parts by weight of the same organic binder as used in the production of the preform, or a dispersant such as oleic acid,
Prepared by mixing and stirring 1 part by weight or less of an acrylic copolymer, a polycarboxylic acid type surfactant, etc.
It is coated with a layer thickness of ~500 μm. The silicon metal used in the surface treatment agent may have the same properties as those used in the coating agent.

The means for applying these coating agents and surface treatment agents to the preform may be brush coating, spray coating, dip coating, or the like, depending on the shape characteristics of the preform. After coating, drying or curing drying is performed at 100 to 250°C to fix it as a surface layer.

Therefore, when using a base layer, drying or curing drying is repeated at each stage of coating with a base treatment agent and a coating agent.

The preformed body with the dried surface layer formed thereon is then carried into a nitriding reaction sintering furnace and heated at 1100 to 1800°C, more preferably 13
Nitriding reaction and sintering is carried out at 00 to 1500°C for 50 to 100 hours.

As a result, metallic silicon is simultaneously converted into silicon nitride from the surface layer to the center of the preform matrix.

At this time, nitrogen molecules are bonded to the metal silicon powder in the surface layer, and the porosity in the surface layer decreases, so the boron nitride and aluminum nitride in the surface layer are baked and hardened, and the binder, the generated silicon nitride, is Since the base material is integrated with the reactive sintered silicon nitride bonded sintered matrix, the surface layer formed is firmly integrated with the reactive sintered silicon nitride bonded sintered matrix.

50 parts by weight of metallic silicon with a purity of 99.9% by weight and a particle size of less than 10 μm, and 50 parts by weight of silicon carbide with a purity of 99.8% by weight and a particle size of less than 10 μm in a polyvinyl alcohol aqueous solution with a concentration of IO% by weight 3 parts by weight were kneaded with Ni-gu, filled into a cylindrical rubber mold with an inner diameter of 50 mφ and a length of 500 fl, and was subjected to isostatic pressure molding ((, IP) under cold isostatic pressure of 1000 kg/c + J. The mold was removed and cured at room temperature for 5 hours, and then dried and cured in a drying oven at 150° C. for 10 hours to produce a preform.

On the other hand, a coating agent was mixed with boron nitride and aluminum nitride, each having a particle size of less than 10 μm and a purity of 98% by weight, and a particle size of 1
A mixture of 0 μm or less metal silicon in the proportions shown below was prepared by adding 120 parts by weight of water to 100 parts by weight of each mixture and stirring. In addition, as a surface treatment agent, metallic silicon 1 with a particle size of less than 10 μm is used.
00 parts by weight and 150 parts by weight of water were mixed and stirred.

These coating agents and surface treatment agents were applied to the entire outer surface of the preform with a brush to a predetermined thickness, and dried to form a surface layer.

Subsequently, it was carried into a reaction sintering furnace with a nitrogen gas atmosphere of 0.5 atm, maintained at 1250°C for 20 hours, and then heated at 1400°C for 2 hours.
The reaction sintering process was carried out using a two-step heating method in which the temperature was maintained for 0 hours.

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

For comparison purposes, we produced samples that did not contain metallic silicon in the coating agent or surface treatment agent, and did not form any surface layer, and then underwent nitriding reaction and sintering under the same conditions. A sample was manufactured and subjected to an evaluation experiment. In addition, 1.8 weight of commercially available colloidal boron nitride was added to a silicon nitride reaction sintered body, which was manufactured by subjecting the surface of a metal silicon element molded body made of the same material to nitridation reaction sintering under the same conditions without treatment. A comparative material in which a surface layer of boron nitride was formed using a boron nitride spray agent containing 1% by weight of an organic binder and 1% by weight of an organic binder was prepared and similarly subjected to an evaluation experiment.

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

(Hereinafter referred to as the margin 1 υ Caucage 1 υ Caution This invention is a binder or a nitride, or a nitrogen by a nitrified body layer directly or a mixture of nitride or aluminum nitride or a mixture. The present invention relates to a product formed integrally with a silicon-bonded sintered matrix and a method for producing the same, including: 1) Improving the resistance to molten metal castability of a silicon nitride-based reaction sintered product requires it; The conventional method is performed on a surface layer made of boron nitride or aluminum nitride or a mixture thereof with silicon nitride as a binder formed integrally with the base material, or on a surface layer with a single layer of silicon nitride interposed therebetween. It is possible to provide a reactive sintered silicon nitride bonded sintered body with excellent molten metal castability that is unparalleled in other products at a low cost.

2) Furthermore, when using the manufacturing method of the present invention, a surface layer made of boron nitride or aluminum nitride or a mixture thereof using silicon nitride as a binder is formed simultaneously with the reaction sintering of the silicon nitride reactive sintered matrix itself. The surface layer is formed integrally with the mother body. Therefore, a surface layer with excellent durability not found in conventional methods can be easily obtained with fewer steps.

Excellent practical effects are demonstrated.

Claims (1)

[Scope of Claims] [1] A surface layer made of boron nitride or aluminum nitride or a mixture thereof with silicon nitride as a binder is applied directly to the molten metal contact surface of the reactive sintered silicon nitride bonded sintered matrix or A reactive sintered silicon nitride bonded sintered body having excellent resistance to molten metal casting, characterized in that it is formed through a single element layer. [2] Boron nitride, aluminum nitride, or a mixture thereof is dispersed on the molten metal contact surface of the metal silicon element molded body at a weight ratio of (95:5) to (1:99) with metal silicon. Production of a reactive sintered silicon nitride bonded sintered body with excellent resistance to molten metal casting, characterized in that after coating with a coating agent, reaction sintering is performed at 1100 to 1800°C in a nitrogen gas atmosphere. Method. [3] After coating the molten metal contact surface of the metal silicon element molded body with a surface treatment agent containing metal silicon dispersed therein, boron nitride, aluminum nitride, or a mixture thereof is applied to the metal silicon in a weight ratio of (95 Molten metal casting resistance characterized by coating with a coating agent dispersed at a blending ratio of 1:5) to (1:99) and then reacting and sintering at 1100 to 1800°C in a nitrogen gas atmosphere. A method for producing a reactive sintered silicon nitride bonded sintered body with excellent properties.