JPH04149083A - Carbon material having oxidation resistance at high temperature - Google Patents

Abstract

PURPOSE:To improve oxidation resistance by successively forming a thin SiC- based carbide film, a thin film of a specified metal and a thin film of Ir, Ru or Rh on the surface of a carbonaceous base material. CONSTITUTION:A carbonaceous base material 1 such as a carbon fiber reinforced carbon composite material and a prescribed percentage of a powdery SiC-Si-Al2O3 mixture are heated to a prescribed temp. in a furnace and the surface of the material 1 is allowed to react with the Si to form a thin SiC- based carbide film 2 in about 100mum thickness. A thin film 3 of Hf, Zr, Si, Cr, Ti, Ta, Nb or Al is formed on the film 2 in about 1-10mum thickness by chemical vapor deposition or other method and a thin film 4 of Ir, Ru or Rh is further formed on the film 3 in about 10-100mum thickness by chemical vapor deposition or other method to obtain a carbon material having oxidation resistance at high temp.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to high-temperature oxidation-resistant carbon materials, and more specifically, to heat-insulating carbon materials, carbon fibers, carbon-carbon composite materials, etc. that are provided with high-temperature oxidation-resistant measures. In particular, the present invention relates to a high-temperature oxidation-resistant carbon material that can be advantageously applied to high-temperature components for gas turbines, jet engines, etc., as well as heat-resistant structural materials for spacecraft.

[Conventional technology]

Graphite or carbon fiber reinforced carbon composite material (hereinafter referred to as C/C
Silicon carbide (Sin) has already been put into practical use as a high-temperature oxidation-resistant coating for composite materials (abbreviated as composite materials), and a typical example thereof will be explained with reference to FIG. In Figure 2, 1
2 is a carbonaceous base material, 2 is a Si0 layer, and 4 is a 5102 layer.

The Si0 layer 2 is formed by reacting the surface of the carbonaceous substrate 1 with Si or by chemical or physical vapor deposition.

Further, a silicon dioxide (SiO3) layer 5 is formed by a method such as painting for the purpose of sealing cracks occurring in the Si0 layer 2. The Si0 layer 2 and the SiO□ layer 5 function as an oxidation-resistant coating for graphite or a C/C composite material.

That is, when the SiO2 layer 5 is melted at a high temperature of 1200° C. or higher, it acts as a layer that is difficult for oxygen to pass through. Also, 81
Since the 0 layer 2 has the property of becoming 5tOa by self-oxidation, it has good bonding properties with the S+02 layer 5, and on the other hand, since it is a layer formed by modifying the surface of the carbonaceous base material, Bondability with the base material is also good. The function of the 810 layer 2 is to bond this base material (carbon) and the SiL layer 5, and to prevent carbon oxidation (-generation of carbon oxide) and consumption due to direct contact between the base material (carbon S) and 5in2. (Reference: U.S. Patent No. 4.47192)
3 specification, etc.) Next, the application of iridium (m) as an oxidation-resistant coating for carbonaceous substrates has also been reported.
This will be explained using figures. In Fig. 3, 1 is a carbonaceous base material, 7 is a b layer, and 6 is titanium carbide (TiC) or hafnium carbide (
This is the llf(1') layer. The Ir layer 7 may be directly formed on the base material (carbon) 1 by chemical, physical vapor deposition, electrodeposition, etc., but in order to further increase the adhesion between the B layer 7 and the base material 1. , a TiC layer,) IfCfC layer may be formed on the substrate 1 by chemical vapor deposition and then coated with the 11 layer 7. The Ir layer 7 is difficult for oxygen to pass through, and the above-mentioned 81
It acts as a layer corresponding to layer 02. TiC, Hf[:
The carbide layer 6 reacts with b to form b-Ti, Ir-H
f to form an intermetallic compound. Further, since these carbides contain carbon compared to Ir, they can be expected to have better affinity with the base material (carbon) 1. From these two points, TiC, t(
The purpose is to use the fC layer to improve the adhesion between the Ir layer and the base material (References: J, M, Cr1sc
ione, R,A.

Mercuri, E., P., Schram,
8, W, Sm1th, and H,F.

Volk, “High Temperature
Protective Coatings for G
raphite” ML-TDR-64-173Par
tII Oct.

1974, J, R, 5trife, J, G, S
meggil and W,L.

Worrell “Reaction of I
ridium 1with MetalCaebi
Des in tbe Temporature
Range of 1923 to 2400
K” J, Am, (:er, Soc,, 73 (4
) P 83445, 1990, etc.) [Problems to be Solved by the Invention] First, the method of using SlO□ and SiC as an oxidation-resistant coating has the following problems. Zunawa, Sin. and S
In a system where iC and C coexist, the total vapor pressure of the gases generated at temperatures above 1500°C exceeds 1 atm, which causes bubbles to form within the 5I02 coating, destroying the coating and impairing its oxidation-resistant function (Source :G.

H, 5chiroky, R, T, Pr1ce
, J.E., 5beehan, G.A.

Technologies Report G8-
A 18696 (1,986)) Therefore, S
In the method of using lO, and SiC as an oxidation-resistant coating, the upper limit of the temperature at which it can be stably used is around 1500° C., so it is difficult to use it for a long time at a temperature exceeding this.

Next, the method of using Ir as an oxidation-resistant coating has the following problems. In other words, Ir does not form carbides and has a low solid solubility limit for carbon. The bondability at the interface between hlr and the carbonaceous base material is very poor. Moreover, the coefficient of thermal expansion of 1r is 8 to 10
x 10-s/l: (1000°C or higher), whereas carbonaceous base materials generally have a small coefficient of thermal expansion, especially C/C
In the case of a composite material, the ratio is about 1 to 2 x 10-6/, so when the temperature is raised or lowered due to the difference in thermal expansion coefficient, thermal stress is generated at the interface and the film easily peels off.

Furthermore, in the conventional example of chemical vapor deposition of TiC or HfC between a carbonaceous base material and an Ir layer, there is a possibility that the bondability between lr and carbide can be obtained by an interfacial reaction. However, Ti
The coefficient of thermal expansion of C0 is approximately 8X10-6/℃, and the coefficient of thermal expansion of HfC is approximately 7X1O-'/l, which is about the same as that of Ir, so the difference in coefficient of thermal expansion with the carbonaceous base material is large. TiC.

Since it is not considered that a reaction actively occurs at the interface between HfC and the carbonaceous base material, the problem that this interface peels off due to thermal stress still remains.

Furthermore, in the event that the coating layer 1r is peeled off or otherwise damaged, in the case where Ir is directly coated on the carbonaceous base material, the carbonaceous base material will be directly exposed to high temperatures and will instantly burn out, causing the carbon Damage to the entire equipment that uses high-quality base materials is significant. Furthermore, even if only the TiC and HfC layers remain in an example in which Ir is coated through the TiC and HfC layers, the oxide films produced by oxidation of the surfaces of these carbides, that is, titanium oxide and hafnium oxide, are similar to SiO2 in SiC. Since it does not have a property that makes it difficult for oxygen to pass through, it cannot play a role in preventing oxidation of the carbonaceous base material.

In view of the above-mentioned state of the art, the present invention aims to provide a high temperature oxidation-resistant carbon material that does not have the problems of conventional materials.

[Means to solve the problem]

The present invention provides a thin film consisting of (a) a carbide layer containing silicon carbide as a main component on the surface of a carbonaceous base material, (b) Hf,
Zr, Si, Cr, Ti, T
a, a thin film of any one of Nb and A1, and (
c) A high-temperature oxidation-resistant carbon material characterized by sequentially forming thin films of Ir, Ru, and Rh.

[Effect]

First, in order to solve the problem of conventional technology using SiC and Sin as oxidation-resistant coatings, which cannot be stably used at temperatures above 1500°C, the present invention uses SiC formed on the surface of a carbonaceous base material. The main component is a carbide layer (
SiC and C) are coated with Ir, Ru and Rh! We are trying to solve the problem by doing this. As long as SiC is not oxidized, it is stable up to around 2600°C, and if it is coated with ir, Ru, and Rh, it can be used even at temperatures above 1500°C;
Those coated with 800 to 1850 t', Ir, and Ru can be used up to around 2000 t'.

Next, there is a problem in the conventional technique of directly coating a carbonaceous base material with a single phase of Ir. In order to solve the problem that the interface with the b coating layer is insufficient and peels off easily, in the present invention, a thin film of metal such as Hf is formed on the carbide layer whose main component is SiC, and then the b , Ru and Rh are used to solve the problem. A thin film of metal such as Hf reacts with Ir, Ru, Rh, and SiC through preliminary heat treatment or heating during first use, and plays a role in improving the adhesion of the interface.

Furthermore, Ir or TiC, flfc, which is a problem for both the conventional technique of coating TiC or HfC between Ir and the carbonaceous substrate by vapor deposition, and the conventional technique of coating Ir directly on the carbonaceous substrate. The present invention attempts to solve the problem of peeling due to thermal stress caused by the difference in coefficient of thermal expansion with the carbonaceous base material by the following means. That is, the thin films of Ir, Ru, and Rh are bonded to a carbide layer mainly composed of SIC, and the SiCCD thermal expansion coefficient is 1k 5 ~ 6 x 10
Since the difference in coefficient of thermal expansion between Ir, Ru, and Rh is smaller than that of a carbonaceous base material (particularly a C/C composite material) in terms of -'/, thermal stress caused by temperature fluctuations is small. Moreover, a carbide layer mainly composed of SiC and Ir, Ru and R
Between the layers of h is a metal (Hf) that easily reacts with both.

2r, Si, Cr, Ti, Ta, Nb and A
1) and is difficult to peel off because the adhesiveness at the interface is improved by forming a reaction layer by heating.

Regarding the method of forming an interface between a carbide layer mainly composed of SiC and a carbonaceous base material, there has already been a conventional technique in which a carbonaceous base material is reacted with a carbide-forming element such as Si to form a carbide layer on the surface of the carbonaceous base material. It is also possible to obtain an interface that does not concentrate thermal stress and is difficult to peel off by gradually changing the ratio of carbon to carbide by forming a carbide layer using a method of oxidation.

Another common problem with conventional techniques using Ir as a coating layer is rapid burnout of the carbonaceous base material after the Ir layer is damaged.
Even if the u and Rh layers are damaged, it can be expected that the intermediate layer SiC exhibits oxidation resistance and can prevent rapid burnout of the carbonaceous base material.

The structure of the high-temperature oxidation-resistant carbon material of the present invention will be explained in more detail with reference to FIG.

In FIG. 1, 1 is a carbonaceous base material, and 2 is a film thickness of 1o.

It is a carbide layer thin film mainly composed of SiC of about μm,
3 is Hf, Zr, Si, Cr, Ti, Ta,
It is a metal thin film of either Nb or A1, and this metal layer thin film 3 is formed by a method such as chemical vapor deposition, physical vapor deposition, electrodeposition, etc., and the film thickness is about 1 to 10 μm. . 4 is a thin film of Ru, Rh, and Ru. This thin film 4 can also be formed by chemical vapor deposition, physical vapor deposition, electrodeposition, etc., and has a thickness of about 10 to 100 μm.

The carbide layer thin film 2 mainly composed of SiC has the role of gradually changing the difference in thermal expansion coefficient between the carbonaceous base material 1 and the Ir, Ru, and Rh thin film 4. Also, b.

If the Ru and Rh thin film 4 is damaged, it will - temporarily protect the carbonaceous substrate from rapid burnout. Next, Hf, 2r
, Si, Cr, Ti, Ta, Nb, and A1 metal thin film 3 has SiC as its main component due to heating during film formation by chemical vapor deposition, physical vapor deposition, etc., or due to the effect of heating when initially used at high temperature. The carbide layer thin film 2 reacts with the Ir, Ru, and Rh thin films 4 and plays a role in improving the adhesion of the interface.

In order to promote this interfacial reaction, it is also effective to perform heat treatment after film formation.From the above viewpoint, Ir, Ru and Rh
The criteria for selecting the metal to be used between the thin film 4 and the carbide layer thin film 2 mainly composed of SiC are: ■ It must have lower carbide formation energy than Si, and ■ It must be a solid solution in Ir, Ru, and Rh, or it must be stable. Two points were adopted: forming a compound.

Table 1 shows the carbide formation energy of the selected elements and Ir
(Representative example)

On the other hand, Ir, Ru, and Rh4 function as a high-temperature oxidation-resistant coating on the carbonaceous base material. Ir, Ru, and Rh are stable as metals at high temperatures, and are less consumed by oxidation than other high-melting point metals such as molybdenum and tungsten. In particular, among the platinum group elements, Ir, Ru and Rh
has a melting point of around 2000℃ or higher, and has a melting point of 1800℃ or higher.
Acts as an oxidation-resistant film at high temperatures. Although Os has a melting point exceeding 3000° C., it was excluded because it is more volatile and consumed by oxidation than Ir, Ru, and Rh.

〔Example〕

Table 2 shows examples in which coating layers were formed for 32 different configurations. In the examples, C/C is used as the carbonaceous material.
A composite material (50% fiber volume ratio formed from a polyacrylonitrile carbon fiber fabric and a carbon matrix made from phenolic resin) is used, and its surface is
1 (33% C/C composite material in a furnace at 1800℃)
SiC was charged together with 33% Si:33% Atz03 powder and held for 4 hours) to form SiC, and this was used as the base material. Furthermore, a thin film of metal such as Hf was formed thereon by sputtering, and then a film was formed by thermal CVD using chloride such as 1r.

For comparison, the following three types of test materials corresponding to the prior art were used. In other words, an organic compound of Si is coated on a substrate whose surface is made of SiC and then heated to form an S10□ film, a carbonaceous substrate is coated with Ir by direct chemical vapor deposition, and a carbonaceous substrate is further coated with Ir by chemical vapor deposition. After sputtering HfC on top,
There are three types with Ir chemically vapor deposited.

The oxidation resistance and peeling properties of the coating due to thermal stress were compared and examined using the following method for the test materials shown in Table 1 and above. That is, regarding oxidation resistance, the sample was heated continuously for 120 minutes in an atmospheric furnace heated to 1800° C., then taken out, and the change in weight was examined. Regarding thermal stress, the thermal cycle between room temperature and 1800° C. was repeated 10 times in an Ar atmosphere, and the presence or absence of peeling was examined visually and by observing the cut surface.

Next, in order to investigate the effect on the carbonaceous base material after damage has occurred to the coating layer such as Ir, all of the test materials of the present invention and Ir
Two comparative materials coated with Ir were exposed to an oxygen-acetylene flame for 1 minute at 2500° C., which exceeds the melting point of Ir.

Table 3 shows the test results.

As is clear from Table 3, the substrate of the C/C composite material of the test piece (Nα33) coated with SiC and Sin was burnt out in the atmospheric heating test. On the other hand, in the Ir-coated comparative materials (No. 34, Nα35) and the invention product, the outermost coating layer was slightly thinned by oxidation, but the base material was not damaged.

Next, in a thermal cycle test, a comparative material coated with Ir (k34
．． While peeling was observed in all Nα35) products, no peeling was observed in the products of the present invention.

Furthermore, a comparative material (N
α34. While the carbonaceous base material of Nα35) was considerably burnt out, the amount of carbon burnt out was small in the product of the present invention.

〔Effect of the invention〕

As described in the examples, the high temperature oxidation resistant carbon material of the present invention has the following properties:
Conventional SiC and S10. The oxidation-resistant coated carbon material shown in Fig. 1 shows excellent oxidation resistance even at temperatures above 1,500°C, where the oxidation-resistant function is impaired.

Furthermore, since the concentration of thermal stress due to the difference in thermal expansion coefficient between the coating layer and the base material, which is a major technical issue for oxidation-resistant coatings on carbonaceous substrates, is suppressed, the peeling resistance of the coating layer is also improved.

Further, a carbide layer mainly composed of Sl and Ir.

Since the Ru and Rh coating layers are combined, it is assumed that I
Even if the coating layers of Ru, Ru, and Rh are damaged for some reason, the oxidation-resistant function of SiC can prevent the carbonaceous base material, which is the base material, from being rapidly burnt out.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a high-temperature oxidation-resistant carbon material according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of a conventional oxidation-resistant coated carbon material with S+02 and SiC, and Fig. 3 is an explanatory diagram of a conventional oxidation-resistant coated carbon material with Ir. FIG. 3 is an explanatory diagram of a carbon material.

Claims (1)

[Claims] (1) On the surface of the carbonaceous base material, (a) a thin film consisting of a carbide layer mainly composed of silicon carbide, and (b) any one of Hf, Zr, Si, Cr, Ti, Ta, Nb, and Al. A high-temperature oxidation-resistant carbon material characterized by forming the above thin film and (c) a thin film of any one of Ir, Ru, and Rh in sequence.