JPH04149082A - Carbon material having oxidation resistance at high temperature - Google Patents

Abstract

PURPOSE:To improve thermal shock resistance by successively forming a thin SiC-based carbide film and a thin film of an alloy based on Ir, Ru or Rh on the surface of a carbonaceous based 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 an alloy contg. >=70wt.% Ir, Ru or Rh is formed on the film 2 in about 10-100mum thickness by chemical vapor deposition or other method by using one kind among Ir, Ru, Rh and one among Cr, Ti, Ta, Nb, Al 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 (Si) 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, ■
2 is a carbonaceous base material, 2 is a Sin layer, and 4 is an 8102 layer.

The Si0 layer 2 is formed by reacting the surface of the carbonaceous substrate 1 with 81 or by chemical or physical vapor deposition.

Further, the silicon dioxide (S102) layer 4 is formed by a method such as painting for the purpose of sealing cracks generated in the Si0 layer 2. The S10 layer 2 and the S]02 layer 4 function as an oxidation-resistant coating for the graphite or C/C composite material.

That is, when the 5lO3 layer 4 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 S1 port 2 through self-oxidation, it has good bonding properties with the 8102 layer 4, and on the other hand, it is a layer formed by modifying the surface of the carbonaceous base material. Therefore, the bondability with the base material is also good. The function of the Si layer 2 is to bond the base material (carbon) and the 5iO7 layer 4, and to prevent carbon oxidation (generation of carbon oxide) and consumption due to direct contact between the base material (carbon) and the 5iO7. (References: U.S. Pat. No. 4, 471)
．． No. 923, etc.) Next, the application of iridium as an oxidation-resistant coating for carbonaceous substrates has also been reported. A representative example of this will be explained with reference to FIG. In Figure 3, 1 is a carbonaceous base material, 6 is an Ir layer, and 5 is titanium carbide (T
ie) or a hafnium carbide (Hf[:) layer. Ir
Although the layer 6 may be directly formed on the base material (carbon) 1 by a method such as chemical or physical vapor deposition or electrodeposition, it is also possible to form the layer 6 directly on the base material (carbon) 1 by a method such as chemical or physical vapor deposition or electrodeposition. , first TiC layer, Hf
A C layer 5 may be formed on the substrate 1 by chemical vapor deposition and then covered with an Ir layer 6. The layer 6 is hardly permeable to oxygen and acts as a layer corresponding to the layer 8102 described above. The carbide layer 5 such as TiC, 1 (fC) reacts with b
-Ti, Ir-1 (forms an intermetallic compound of f).

In addition, since these carbides contain carbon compared to umami, they can be expected to have better affinity with the base material (carbon) 1. Based on these two points, the idea is to use TiC and HfC layers to improve the adhesion between the Ir layer and the base material (references:
J, M, Cr1scione, R,A.

Mercuri, E., P., Schram,
A, W, Sm1th, and old F.

Volk, “High Temperature P.
protective coatings for Gr
aphite″ML-TDR-64-173Partl
l Oct.

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

Worrell “Reaction of Iricl”
with Metal Caebides in
the Temporature Range of
1923 to 2400 K”, J, Am, Ce
r, Soc,, 73 (4) P 83445,
(1990, etc.) [Problems to be Solved by the Invention] First, the method of using the above-mentioned S10° and SiC as an oxidation-resistant coating has the following problems. That is, 5i
In a system where O9, SiC, and C coexist, the total vapor pressure of the gas generated above 1500°C exceeds 1 atm, so 510
Bubbles are generated within the film of No. 2, which destroys the film and impairs its oxidation resistance (Source: G, H, 5chiroky)
, R.T., Pr1ce, J.E.

5heehan, G., A. Technol
ogies Report GA-A18696
(1986)). Therefore, in the method of using SiO2 and SiC as an oxidation-resistant coating, the upper limit of the temperature at which it can be stably used is around 1500°C, and it is difficult to use it for a long time at a temperature exceeding this.

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

Furthermore, in the conventional example of chemical vapor deposition of TiC and HfC between a carbonaceous base material and an Ir layer, there is a possibility that the bondability between Ir and carbide can be obtained by an interfacial reaction. However, Ti
The thermal expansion coefficient of C is about 8 x 10/℃, and the thermal expansion coefficient of HfC is about 7 x 10-6/l, which is about the same as that of Ir, so the difference in thermal expansion coefficient with the carbonaceous base material is large. TiC formed by.

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 temperature and will be burned out instantly. Significant damage to the entire equipment that uses carbonaceous base materials. Also, TiC.

This is an example in which Ir is coated through a HfC layer, and it is assumed that TiC is used.

Even if only the HfC layer remains, the oxide films produced by the oxidation of these carbide surfaces, i.e., titanium oxide and hafnium oxide, are likely to form on carbonaceous substrates, such as 5i02 in SiC, which have a property that makes it difficult for oxygen to permeate. It cannot play its role in preventing oxidation.

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 (1) on the surface of a carbonaceous base material, (a) a thin film consisting of a carbide layer containing silicon carbide as a main component, and (b) Cr.

A high-temperature oxidation-resistant carbon material characterized by sequentially forming a thin film made of an alloy of Ti, Ta, Nb, and A1 and either IrRu or Rh.

(2) A high-temperature oxidation-resistant carbon material, characterized in that the content of Ir, Ru, and Rh in the thin film made of the alloy of (1) is 70% by weight or more.

It is.

[Effect]

First, in order to solve the problem of conventional technology that uses SiC and SiO□ as oxidation-resistant coatings, which cannot be used stably 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 (
A solution is being sought by forming a thin film of an alloy containing b, Ru, and Rh as main components on top of SiC and C). SiC is stable up to around 2600℃ unless it is oxidized, and since it is coated with an alloy mainly composed of Ir, Ru and Rh, it can be used even at temperatures above 1500℃. Maximum 1800~1
850℃, fr, Ru-based alloys have a maximum of 200℃
It can be used even at temperatures close to 0°C.

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 Ir coating layer has insufficient bonding properties and is easily peeled off, in the present invention, a metal that is reactive with carbides mainly composed of SiC is added to Ir, Ru, and Rh. We are trying to solve the problem by adding That is, the aim is to improve adhesion by causing a reaction at the interface between the coating layer and the carbide layer due to the effect of heat treatment after coating the alloy or heating during first use.

Furthermore, Ir or Ti [: , The present invention attempts to solve the problem of peeling due to thermal stress caused by the difference in coefficient of thermal expansion between HfC and the carbonaceous base material by the following means. That is, Ir, R
The thin film of the alloy mainly composed of u and Rh is bonded to the carbide layer mainly composed of SiC, and the coefficient of thermal expansion of SiC is about 5 to 6X10-6/'C. C
Since the difference in coefficient of thermal expansion with alloys whose main components are Ir, Ru, and Rh is smaller than that of composite materials, the thermal stress caused by temperature fluctuations is small. Moreover, the alloy easily reacts with carbides and contains additive elements (Cr, Ti, etc.).

The adhesion of the interface is improved due to the effect of any one of Ta, Nb, and Al, making it difficult to peel off.

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.

The present invention solves the rapid burnout of the carbonaceous base material after the b layer is damaged, which is another common problem in conventional techniques using Ir as a coating layer.
Even if the alloy layer containing u and Rh is damaged, the intermediate layer SiC exhibits oxidation resistance, so it can be expected to 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, 2 is a thin carbide layer mainly composed of SIC with a film thickness of about 100 μm, and 3 is an Ir
, Ru and Rh, and Cr, Ti,
An alloy thin film of Ta, Nb and A1,
This alloy thin film 3 is formed by chemical vapor deposition, physical vapor deposition, electrodeposition, etc., and the film thickness is practically 1.
It is 0 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 alloy thin film 3. Also, if the alloy thin film 3 is damaged, it will temporarily protect the carbonaceous substrate from sudden burnout. Next, the alloy thin film 3 is heated by chemical vapor deposition, physical vapor deposition, etc. during film formation, or by the effect of heating when initially used at high temperature.
It reacts with the carbide layer thin film 2 whose main component is C, and improves the adhesion of the interface. In order to promote this interfacial reaction, it is also effective to perform heat treatment after film formation. From this point of view, as a criterion for selecting alloying elements, those having properties that have lower carbide formation energy than Sl were selected.

On the other hand, consideration must be given to ensure that the oxidation-resistant functions of Ir, Ru, and Rh are not impaired by alloying.

From this point of view, Ir is used as a criterion for selecting additive elements.

Metals that form stable compounds with Ru and Rh, and in turn promote the intrusion of oxygen by internal oxidation under a high-temperature oxidizing atmosphere, were excluded.

Table 1 shows the carbide formation energy and reactivity with Ir (representative example) of alloy additive elements selected from the above selection criteria.

On the other hand, Ir, Ru, and Rh function as a high-temperature oxidation-resistant coating on the carbonaceous base material. lr, Ru, and [lh 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 have melting points of around 2000°C or higher, and function as an oxidation-resistant film at high temperatures of 1800°C or higher. The melting point of O8 is 3000℃
However, it was excluded because its volatile consumption due to oxidation is significant compared to Ir, Ru, and Rh.

The platinum group elements Ir, Ru, and Rh have the function of preventing oxygen permeation, and if the amount of alloying elements increases, this function may be inhibited, so the amount of alloying elements added should be limited. It is preferable. If the added alloying element is within 10% by weight, all of the above alloying elements are Ir, Ru and R.
It forms a solid solution in h, or forms a two-phase structure with a high melting point compound, and does not inhibit the functions of lr, Ru, and Rh. However, if these alloying elements exceed 30% by weight, adverse effects such as a decrease in the melting point of the alloy (compound) will occur, so Ir
, the amount of Ru and Rh should be 70% by weight or more,
Particularly preferred is 90% by weight or more.

〔Example〕

Table 2 shows examples in which coating layers were formed for 20 different configurations. In the examples, C/C was used as the carbonaceous base material.
A composite material (50% fiber volume ratio formed from a polyacrylotrile carbon fiber fabric and a carbon matrix made from phenolic resin) is used, and its surface is
1 (33% C/C1 composite material in a 1800°C furnace)
SiC, 33%Si:33%A (charged with 1.203 powder and held for 4 hours) to form SiC, was used as the base material. Thereon, an alloy film of Ir, Ru, Rh, and the additive elements shown in Table 1 was formed by chemical vapor deposition using chloride.

For comparison, the following three types of test materials corresponding to the prior art were used. In other words, 81 organic compound was coated on the substrate with the above-mentioned surface made of SIC, and then heat treated to form two S1 coatings, one in which 1F was directly chemically vapor deposited on the carbonaceous substrate, and one in which 1F was directly chemically vapor deposited on the carbonaceous substrate. There are three types in which HfC is vapor-deposited on the material and then Ir is vapor-deposited on the material.

The oxidation resistance and peeling properties of the coating due to thermal stress were compared and examined using the following method for the following test materials. 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. For thermal stress, room temperature and 1800℃ in Ar atmosphere
The thermal cycle was repeated 10 times, 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 subjected to NM in 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 test piece (No. 21> coated with SiC and SiO
The composite material substrate was burnt out. On the other hand, in the comparative materials coated with lr (No. 22.N123) and the products of the present invention, the outermost coating layer was slightly thinned by oxidation, but the base material was not damaged.

Next, in a thermal cycle test, comparative materials coated with Ir (No.
22. While peeling was observed in all Nα23) products, no peeling was observed in the products of the present invention.

Furthermore, a comparative material coated with Ir (N
α22. In N[123], the carbonaceous base material was considerably burnt out, whereas in the product of the present invention, the amount of carbon burnt out was small.

〔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 oxidation-resistant coated carbon materials made of SiC and 5102 exhibit excellent oxidation resistance even at temperatures above 1500°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 containing SiC as a main component and Ir.

Since the coating layer of the alloy containing Ru and Rh is combined, even if the coating layer of the alloy containing Ir, Ru, and Rh is damaged for some reason, the oxidation-resistant function of SiC will protect the carbonaceous base material, which is the base material. can prevent sudden burnout.

[Brief explanation of drawings]

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 made of 5102 and SiC, and Fig. 3 is an explanatory diagram of a conventional oxidation-resistant coating. FIG. 3 is an explanatory diagram of a carbon material.

Claims (2)

[Claims] (1) On the surface of the carbonaceous base material, (a) a thin film consisting of a carbide layer mainly composed of silicon carbide, (b) one of Cr, Ti, Ta, Nb, and Al and Ir, Ru, and Rh. A high-temperature oxidation-resistant carbon material characterized by sequentially forming thin films made of an alloy with one of the above. (2) A high-temperature oxidation-resistant carbon material, characterized in that the content of Ir, Ru, and Rh in the thin film made of the alloy according to claim (1) is 70% by weight or more.