JP2718777B2 - Method for producing reaction sintered ceramic member - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a reaction-sintered ceramic member having improved surface roughness, thermal shock resistance, abrasion resistance and the like.

[Prior Art] For example, when improving the cycle time in producing a ferrous casting or the like, or achieving directional solidification, the amount of molten metal supplied to a mold and the molten metal time are accurately determined. Control is considered extremely important in obtaining good products.

In this case, the material of the nozzle member mounted on the pouring port of the mold is particularly important for achieving the above object. That is, in order to accurately supply a predetermined amount of molten metal to the mold in a predetermined time, the nozzle member needs to have a constant diameter and a low wettability to the molten metal. Further, since the nozzle member is used at a high temperature, it is required to have heat resistance, and is also required to have thermal shock resistance because it comes into contact with a high-temperature molten metal instantly.

Conventionally, as such a nozzle member, for example, a reaction sintered body that has small dimensional shrinkage and is easy to manufacture has been used.

[Problems to be Solved by the Invention] However, a reaction sintered body is usually obtained by nitriding or carbonizing silicon or the like. At this time, a flow path in which a raw material gas nitrides silicon or the like is formed. It is difficult to densify the reaction sintered body. That is, pores of several tens to several hundreds μm are distributed in the reaction sintered body along with the formation of such a flow path. As a result, the conventional reaction sintered body has problems that it is difficult to improve the surface roughness, the strength level is low, and the thermal shock is weak.

For example, in the case of casting a product, conventionally, a reaction sintered body that produces graphite or the like is used as a nozzle member, but according to a reaction between a molten metal component and carbon of a nozzle member in a molten metal passage of the nozzle member. There is a possibility that foreign matter is attached or vapor-deposited, and there is a problem that it becomes impossible to control the pouring speed or the like due to a change in the nozzle diameter.

Therefore, as a nozzle member material whose nozzle diameter hardly changes, a material obtained by hot press sintering and machining a hexagonal boron nitride (h-BN) is used, but it is not only expensive but also h-BN. There is a problem that the material itself is soft and mechanically damaged and worn quickly. There was also a problem that h-BN was easily oxidized.

The present invention has been made to overcome the above-mentioned disadvantages, and is intended to provide a reaction sintered ceramic member capable of improving various properties such as surface roughness, lubricating ability, strength, thermal shock resistance, and wear resistance. It is intended to provide a manufacturing method.

[Means for Solving the Problems] In order to achieve the above objects, the present invention provides at least silicon nitride, sialon, silicon carbide, or a composite material thereof, or silicon nitride, sialon, or silicon carbide. A composite material of one kind and hexagonal boron nitride,
After forming a reaction sintered body by reaction sintering, a ceramic slurry containing silicon nitride as a main component and containing 20 to 95% by weight is applied to the surface of the reaction sintered body and sintered. I do.

[Function] In the present invention, a compression reaction is applied to the reactive sintered body by applying and sintering a ceramic slurry containing silicon nitride as a main component and containing 20 to 95% by weight on the surface of the reactive sintered body. Is done. Thereby, the strength and thermal shock resistance of the reaction sintered body are improved, and the surface roughness of the surface is reduced, whereby the lubricity of the surface is improved and the wear resistance is also improved.

Example Next, a preferred example of a method for manufacturing a reaction sintered ceramic member according to the present invention will be described in detail with reference to the accompanying drawings.

In the production method according to the present invention, a ceramic slurry is applied to the surface of the reaction sintered body. As the reaction sintered body, silicon nitride, sialon, silicon carbide, or
These composite materials, or composite materials with these hexagonal boron nitride (h-BN) are used. The thickness of the coating layer of the ceramic slurry is preferably 1 to 1000 μm, and more preferably about 50 to 300 μm.
By sintering the coating layer, a compression reaction is given to the reaction sintered body. Although it is difficult to treat the magnitude of this compressive stress quantitatively, it is considered that a larger value is better. The magnitude of the compressive stress depends on the strength of the applied coating layer and the particle size of the powder constituting the coating layer. In this case, the particle size of the powder used is preferably 10 μm or less. The ceramic slurry should be selected according to the usage environment, for example, Y ₂ O ₃ 5% by weight,
Al ₂ O ₃ 4% by weight, CeO ₂ 1% by weight, Si ₃ N ₄ 90% by weight,
Alternatively, h-BN 20% by weight, Al ₂ O ₃ 10% by weight, Y ₂ O ₃ 7% by weight, Si ₃ N ₄ 63% by weight are selected, and the dispersion medium is water, alcohol, water + alcohol, Hexane or the like is used. Coating is brushing, dipping,
This is performed by a method such as spray coating. After drying, the reaction sintered body is fired again at a temperature of 1600 to 1900 ° C. The surface roughness after firing is _Rmax = 10 μm or less, which is in the range of about 1 to 2 μm. As a result, the lubricity of the surface is improved, and the wear resistance is extremely improved.

For example, when the reaction sintered body obtained by the present invention is used for a nozzle member for casting, the nozzle member is broken due to repeated thermal expansion due to intrusion of a molten metal component, ingot of metal ingot, slag infiltration, and the like. However, in the present invention, since the surface of the nozzle member was coated with the coating layer of the ceramic slurry, the molten metal component did not penetrate, and destruction due to a so-called wedge effect caused by a metal ingot was observed. It has not been.

The compressive stress applied to the reaction sintered body by the coating layer is obtained by the growth, rearrangement, and densification of particles during sintering, and is determined by the amount of shrinkage, material strength, and coating thickness. In the case of the present invention, the shrinkage of the coating layer is a linear change rate of 5 to 20%, which is a large value.

When the coating layer is excessively thick, cracks occur during sintering and the material is damaged. When the coating layer is extremely thin, the effect of the coating is not obtained, and the cost is merely increased. When the coating is thin, the coating particles adhere to each other, and the sintering of the particles hardly progresses. No strengthening due to compressive stress on the consolidated body occurs.

In addition, when such coating is performed by vapor deposition by the CVD method or the PVD method, a smooth material can be formed, but a significant improvement in physical properties cannot be obtained only by smoothing. Furthermore, in this case, the compressive stress is very small and is not cost effective.

 Next, specific examples will be described.

FIG. 1 is a schematic sectional view of a nozzle member for casting which is a specimen of the present embodiment, and FIG. 2 is a schematic sectional view showing a configuration of a casting system to which the nozzle member shown in FIG. 1 is applied.

In the mold casting system shown in FIG. 2, a molten metal 12 supplied from a ladle 10 is once poured into a hopper 14, and then is poured into a mold 20 through a nozzle member 18 attached to a sprue of a runner 16.
The molten metal is poured into the cavity (not shown) defined in the above. Next, after the molten metal 12 poured into the cavity is cooled and solidified, the mold is opened and the product is taken out from the mold 20. In this case, as shown in FIG. 1, the nozzle member 18 was formed by coating a ceramic slurry on the entire outer surface of a reaction sintered body 22 made of a ceramic material to form a coating layer 24 and sintering the coating layer. It is composed of things.

Here, in the present embodiment, the ceramic slurry was applied to the reactive sintered body 22 made of the material No. 8 shown in the table of FIG. 3, and the comparative examples No. 1 to No. 7 were used. And contrasted.

In this case, No. 4 and the coated No. 8 show extremely good results. In the case of No. 4, 1200 cycles / day.times.30 days or more, and in the case of No. 8, 1200 cycle/
The service life of 90 days or more was shown. One month later, however, pitting occurred in part of No. 4 and the hole diameter increased from 13 mmφ to 14 mm.
Expanded by 1 mm to mmφ. On the other hand, the one coated with No. 8 showed no increase in the hole diameter or pitting corrosion, and was extremely good. In addition, since the hot-pressed product of only h-BN expands by about 1 mm in one week, the improvement of the durability is immeasurable.

The coating layer 24 is composed of 70% by weight of Si ₃ N ₄ having an average particle diameter of 0.7 μm, 10% by weight of Al ₂ O _{3 having} an average particle diameter of 0.4 μm, and an average particle diameter of 0.6 μm.
A dispersion medium was added to a ceramic slurry composed of 5% by weight of Y ₂ O ₃ and 15% by weight of h-BN, and water was used as a solvent.
The mixture was ball milled for hours and brushed to form. _{Si 3 N 4 + (h-} BN) 20 wt% of the reactive sintered body, Si75 wt%, Al5 wt%, h-BN 2 hours N ₂ 20 wt% at 1500 ° C.
It is obtained by baking in the air. After brushing the ceramic slurry on the reaction sintered body 22, at 80 ° C.
It was kept for 24 hours, then dried by heating to 480 ° C., and baked in an N ₂ atmosphere at 1750 ° C. for 30 minutes. The compression of the coating layer 24 was 210 μm, and the apparent Hmv was 1200 kgf / mm ² .
The surface roughness is approximately 1.8 μm. In addition, when the coated and uncoated ones were tested as thermal shock temperature ΔT by the underwater drop method, those without the coating showed heat resistance up to about 500 ° C, and those with the coating showed heat resistance up to 900 ° C. . As described above, when compressive stress is applied to the member by coating, the thermal shock resistance, abrasion resistance, and mechanical properties change significantly, and it has been found that those which could not be used until now can be put to practical use. Was.

[Effect of the Invention] In the method for producing a reaction sintered ceramic member according to the present invention, silicon nitride, sialon, silicon carbide, or
A reaction sintered body is formed by reacting and sintering these composite materials or a composite material of at least one of them and hexagonal boron nitride, and the surface thereof contains silicon nitride as a main component in an amount of 20 to 95% by weight. By compressing and sintering the ceramic slurry to be contained, a compressive stress is applied to the reaction sintered body. As a result, the heat shock resistance and the wear resistance can be improved, so that the effect of greatly expanding the application to casting parts and the like can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a casting nozzle member obtained by the method of the present invention, and FIG. 2 is a case where the reactive sintered ceramic member obtained by the method of the present invention is applied to a casting nozzle member of a mold casting system. FIG. 3 is a table showing examples and comparative examples of the reaction sintered ceramics member obtained by the method of the present invention. 18 ... Nozzle member, 22 ... Sintered sintered body 24 ... Ceramic slurry

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C04B 35/56 101D 101X

Claims (2)

(57) [Claims] 1. A reaction sintering of silicon nitride, sialon, silicon carbide, or a composite material thereof, or a composite material of at least one of silicon nitride, sialon, and silicon carbide and hexagonal boron nitride. Forming a reactive sintered body by the method described above, and applying a ceramic slurry containing silicon nitride as a main component and containing 20 to 95% by weight on the surface of the reactive sintered body, followed by sintering. Manufacturing method of the member. 2. The method according to claim 1, wherein the thickness of the ceramic slurry is 1 to 1000 μm.