JP2673330B2 - Method for forming composite protective coating on ceramic compact - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a composite protective film on a ceramic molded body, which is formed on the surface of a member having a contact portion with a molten metal in the atmosphere. Examples of the member include a heater tube, a thermometer protection tube, a furnace wall, a runner, a spout insert, etc. which accompany a molten metal handling device of a casting device.

[0002]

2. Description of the Related Art Here, a member associated with an apparatus for handling molten metal of aluminum (including alloy) will be mainly described as an example, but the same applies to a member associated with an apparatus for handling molten metal such as zinc or magnesium.

The required quality of the associated members of the apparatus for handling molten metal is that it can withstand a temperature above the melting point of the molten metal, that it is not corroded by the molten metal, and that it does not corrode in a high temperature atmosphere.

Conventionally, cast iron has been mainly used as a molding material for the above-mentioned members. However, cast iron has a drawback that its life is short because it is deformed by the growth of graphite. Therefore, ceramic materials such as alumina, magnesia, and silicon carbide have come to be used as substitutes for cast iron, and particularly silicon nitride having excellent thermal shock resistance has been used (Japanese Patent Laid-Open No. 2-3).
8391 gazette).

[0005]

However, a flux (alkali / alkaline earth metal salt, etc.) is usually added to the molten aluminum in order to ensure castability. Therefore, the flux component reacts with silicon nitride, resulting in melting and damage of silicon nitride.

[0006] Another problem is that the flux-containing slag (component example: Al ₂ O ₃ 86.5 wt%, MgO: 2.9 wt%
_{%, Si O 2: 2.8wt%} , Na 2 O: 5.1wt%, Na
(F: 1.2 wt%) adheres and cannot be easily peeled off. Forcibly peeling results in the destruction of the silicon nitride base material.

Zirconia is a material that does not react with the flux component and does not adhere to the flux, but zirconia is vulnerable to thermal shock, and there is a limit when used alone as a member.

Therefore, in order to utilize the advantages of both silicon nitride, which is resistant to thermal shock, and zirconia, which is resistant to flux attack, a material having a sprayed coating of zirconia on the surface of silicon nitride is considered.

However, silicon nitride is not well compatible with ordinary metals and ceramics, and if it is simply sprayed, a practical material having a zirconia-based sprayed coating on the surface of silicon nitride cannot be obtained.

The member that comes into contact with the molten aluminum has the zirconia coating firmly adhered to the silicon nitride base material, does not peel off even when subjected to a rapid thermal shock, and the sprayed coating is as dense as possible. It is required to have a property of preventing the invasion of the aluminum alloy and not being corroded by the aluminum alloy.

In view of the above, the present invention provides a method for forming a composite protective film having the above-mentioned properties on the surface of a silicon nitride molded body (ceramic molded body).

[0012]

In the present invention, in order to solve the above-mentioned difficulties and to obtain a ceramic molded body which is resistant to thermal shock and excellent in flux attack resistance, first, the surface of the silicon nitride molded body is wetted with the wettability with the silicon nitride molded body. After spraying a good high-melting-point transition metal, impregnating it with a glassy substance and firing it, spraying an intermediate coating consisting of a high temperature oxidation resistant alloy, finally spraying stabilized zirconia, and further coating the zirconia coating with an organosilicon polymer. A method of forming a composite protective film of a ceramic molded body, which is impregnated with and fired, was conceived.

The configuration of each of the above means will be described in detail below. FIG. 1 is a diagram for explaining the structure of a molten metal thermometer protective tube to which the method for forming a composite protective film of the present invention is applied. (1) The flame-spraying of the refractory metal may be flame spraying, but it is usually performed by plasma spraying which causes less deterioration of the sprayed material. The high melting point metal spray coating 3 has a thickness of 10 to 70 μm.
The degree is good. If the thickness is less than 10 μm, a problem tends to occur in the adhesion between the silicon nitride base material (ceramic molded body) 1 and the upper layer high temperature oxidation resistant alloy sprayed coating 5. On the other hand, when the thickness exceeds 70 μm, the coating film is likely to peel off due to the thermal stress generated by heating and cooling.

Examples of the high melting point transition metal having good wettability with silicon nitride include Mo, Nb, and W, which relatively easily cause a diffusion reaction with silicon nitride.

(2) In the impregnation and firing treatment of the above-mentioned high melting point metal sprayed coating 3 with a glassy substance, a glassy substance dispersed in a solvent is applied by spraying, dipping, brush coating, etc., and then dried. -After preheating, heat to about 850 ° C and fire. This glassy impregnation / firing is carried out in order to secure an initial bonding force until the refractory metal spray coating 3 diffuses into the silicon nitride base material by the heat of the molten metal to form a nitride. is there. The coating amount of the glassy material is 10 to 30 g / m ^{2 in} terms of solid content.

The above-mentioned glass substance is mainly composed of sodium silicate and sodium aluminate. Further, an oxide such as SiO ₂ , MgO or Al ₂ O ₃ or a metal such as Si, Al or Fe may be added thereto.

(3) The high temperature oxidation resistant alloy spray coating 5 is usually formed by plasma spraying, as in the case of the high melting point spray coating 3. The high temperature oxidation resistant alloy sprayed coating 3 may have a thickness of about 50 to 120 μm. If it is less than 50 μm, it is difficult to exert the effect of relaxing the thermal expansion difference among the zirconia-based sprayed coating 5, the silicon nitride base material 1 and the high melting point alloy layer 6, and if it exceeds 120 μm, the thermal stress generated by heating and cooling is increased. Therefore, the coating film is easily peeled off.

As the above-mentioned high temperature oxidation resistant alloy, a Co alloy is usually used which is not easily corroded by a high temperature molten alloy and is resistant to high temperature oxidation. Specifically, co-clary (Co-Cr-Al-Y based alloy) or stellite (Co
-Cr-W type alloy), and the like. The composition of coklarie is Cr: 20-30 wt%, Al: 10-20 wt%,
Y: 0.5 to 2.0 wt% Co: balance, and the composition of stellite is Cr: 20 to 30 wt%, W: 3 to 10 wt%, C
Each range of o: balance is preferable.

(4) The zirconia-based sprayed coating is formed in the same manner as the high melting point sprayed coating 3. The film thickness of the zirconia-based thermal spray coating 7 is 120 to 180 μm.
If it is less than 120 μm, the effect of improving the non-adhesiveness to the molten metal is difficult to be obtained, and if it exceeds 180 μm, further increase in the effect cannot be expected, which is economically disadvantageous.

Here, as the zirconia-based material, not only those having a zirconia (ZrO ₂ ) main component but also alumina-rich alumina-zirconia (Al ₂ O ₃ / ZrO) are used.
₂ ) is also included. Zirconia is originally strong against flux attack, but in order to suppress expansion due to transformation, Y ₂ O ₃ , CaO, CeO, Al ₂ O ₃ , MgO, etc. are added as stabilizers in the amount of 2.0 to 15.0 wt%, so-called stable. It is desirable to use zirconia oxide.

(5) In the impregnation and firing treatment of the zirconia-based thermal spray coating 7 with an organic silicon polymer, a dispersion of an organic silicon polymer powder in an organic solvent is applied to the surface of the thermal spray coating by brushing or spraying. And after drying,
It is heated and baked at 500 ℃ or more to be integrated with the zirconia coating. . The coating amount of the organosilicon polymer is 5 to 25 g / m ^{2 in} terms of solid content.

This sealing treatment seals the fine pores originally possessed by the zirconia-based sprayed coating to prevent the intrusion of the molten metal from the area, and also strengthens the tissue bonding force of the zirconia-based sprayed coating, resulting in thermal shock. The purpose is to prevent the occurrence of cracks.

As the above-mentioned organosilicon polymer compound,
Ladder type silicon oligomers and the like can be mentioned.

The zirconia film formed by such a method has excellent oxidation resistance and can withstand molten metal attack and flux attack well, so that when it is used for metal molten metal treatment equipment members, a product with significantly improved durability can be obtained. .

[0025]

In the present invention, in forming a zirconia film which is resistant to flux attack on the surface of a silicon nitride molded article having excellent thermal shock resistance, first, M which easily reacts with silicon nitride.
o, Nb, W and other high melting point metals are sprayed, and the sprayed coating is impregnated with a vitreous substance and fired to serve as an anchor, and then the thermal expansion difference between silicon nitride and zirconia is relaxed, Moreover, a spray coating of high temperature oxidation resistant alloy that can withstand the attack of molten metal or flux is formed, a zirconia spray coating is formed on it, and the zirconia spray coating is impregnated with an organic silicon polymer and baked to form a zirconia layer. The micropores generated at the same time are sealed and the bond strength within the coating of the zirconia-based thermal spray coating is strengthened to prevent the occurrence of cracks due to thermal shock.

[0026]

【Example】

A. Silicon nitride thermometer protection tube (outer diameter 30φ x length 400m
After roughening the surface of m) by blasting, the following steps are performed in the combinations shown in Table 1 to form a zirconia-based sprayed coating on the outermost surface, and the ceramic laminate of each of the examples and comparative examples is formed. Manufactured body. In the following description, “%” and “ratio” indicating the composition are by weight unless otherwise specified.

(1) High melting point metal spraying ... Mo powder (particle size: 1
0 to 53 μm) or Nb (particle diameter: 10 to 53 μm), and plasma spraying is performed at a film thickness of 10 to 20 under the following conditions.
It performed so that it might be set to micrometer.

Plasma gas: Ar / H ₂ , current: 50
0A, spraying distance: 120 mm (2) Glass impregnation / calcination treatment 10 wt% dispersion liquid (dispersion medium: water / ethanol = 1/1) of fine glass powder having the following average particle size and composition was applied on the high melting point sprayed coating. Brush applied from (coating amount: solid content conversion 20
g / m ² ), and after drying, 1 in an N ₂ gas atmosphere furnace
Holding at 50 to 200 ° C. for 2 hours → heating to 850 ° C. over 1 hour, holding for 15 minutes or more, and firing.

5 μm, Na ₂ O 3.5%, SiO ₂
52% Al 22%, Fe 13%, Co 13% (3) High temperature oxidation resistant alloy spraying Coclary powder (particle size 10-45μ)
m) or stellite powder (10 to 45 μm), and plasma spraying under the following conditions to a film thickness of 80 to 100 μm.
It was done so that

Cr: 23%, Al: 13%, Y: 0.6
% Co: balance, Cr: 28%, W: 4%, C: 1.0%, Mo: 1.0
%, Co: balance, plasma gas: Ar / H ₂ , current: 500 A, spraying distance: 120 mm (4) Stabilized zirconia spraying Stabilized zirconia powder with the following compositions (particle size: 10
.About.45 .mu.m) and plasma spraying was performed under the following conditions to a film thickness of 80 to 100 .mu.m.

Zr O ₂ : 91%, Y ₂ O ₃ : 8.4%,
_{SiO 2: 0.3%, Al 2} O 3: 30%, Zr O 2: 70%, plasma gas: Ar / H _2, current: 500A, spraying distance: 70mm, (5) an organic silicon polymer impregnation and calcination treatment ladder 10 of silicon oligomer powder (flakes)
A wt% dispersion liquid (dispersion medium: ethanol) was applied by brushing on the stabilized zirconia-based sprayed coating (application amount: 13 g / m ^{2 in} terms of solid content), dried, and then in an atmospheric furnace for 1 h.
After raising the temperature to 300 ° C over 30 minutes, hold for 5 hours over 5 hours
After the temperature was raised to 00 ° C., the temperature was maintained for 30 minutes to perform firing.

B. The ceramic laminates (test samples) of the respective examples and comparative examples were used in an aluminum alloy melt having the following composition, and the service life of the protective tube was measured.

Si 16.0% Fe 0.3% Cu 4.5
% Mg 0.5% Al balance The service life was judged by the crack occurrence state of the zirconia-based sprayed coating, and the peeling mode was judged by the peeled state when the adhered noro was forcibly peeled off.

The test results are shown in Table 1. In each of the examples, it can be seen that the composite protective film with no slag did not peel off and the service life was remarkably long.

[0035]

[Effect] According to the method of the present invention, the composite protection of the surface of the silicon nitride base material, which has excellent thermal shock resistance, has excellent resistance to molten metal / flux attack, and excellent thermal shock resistance / high temperature oxidation resistance. A film can be formed. That is, the composite protective coating formed by the method of the present invention is a zirconia-based thermal spray coating impregnated with an organosilicon polymer, a high-melting-point metal thermal-spray coating impregnated with glass and fired, and a high-melting-point metal thermal spray coating and zirconia-based coating. Since it is bonded to the silicon nitride base material through the high temperature oxidation resistant alloy sprayed layer that absorbs the difference in thermal expansion from the thermal spray coating, it is resistant to thermal shock and is less likely to be damaged during repeated heating and cooling. Has the effect of significantly extending the life of the components associated with the.

[0036]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a molten metal thermometer protection tube to which a method for forming a composite protective film of the present invention is applied.

[Explanation of symbols] 1 Silicon nitride base material (ceramic molded body) 3 High melting point thermal spray coating 5 High temperature oxidation resistant alloy thermal spray coating 7 Stabilized zirconia thermal spray coating

Front Page Continuation (72) Inventor Ryuichi Masuda, 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor, Yoshiro Hayashi, 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Invention Mori Makoto Soka Ichiba, Shiojiri City, Nagano Prefecture Showa Denko Co., Ltd. Shiojiri Plant (72) Inventor Yoshio Nishihara Bunkyodai, Fujiyama-ku, Ube City, Yamaguchi Prefecture

Claims (5)

(57) [Claims] 1. A thermal spray coating of a refractory metal is formed on the surface of a silicon nitride molded body, and the thermal spray coating is impregnated with a glassy substance and baked, and then a thermal spray coating of a high temperature oxidation resistant alloy and a zirconia thermal spray coating are formed. A method for forming a composite protective coating on a ceramic molded body, which comprises sequentially forming and finally impregnating the zirconia-based sprayed coating with an organic silicon polymer and baking the same. 2. The method for forming a composite protective coating on a ceramic molded body according to claim 1, wherein the refractory metal is one kind of metal selected from molybdenum, niobium and tungsten. 3. The method for forming a composite protective film on a ceramic molded body according to claim 1, wherein the vitreous substance contains sodium silicate as a main component. 4. The high temperature oxidation resistant alloy comprises Cr: 20 to 30 wt%,
Al: 10 to 20 wt%, Y: 0.5 to 2.0 wt%, balance: alloy having a composition of Co, or Cr: 20 to 30 wt%, W: 3 to
2. The method for forming a composite protective film on a ceramic molded body according to claim 1, wherein the alloy is an alloy having a composition of 10 wt% and the balance: Co. 5. The composite protective film for a ceramic molded body according to claim 1, wherein the zirconia is a stabilized zirconia containing at least one of yttrium oxide, calcium oxide, cerium oxide, aluminum oxide and magnesium oxide. Forming method.