JPH0247359A - Compound construction and manufacture thereof - Google Patents

Abstract

PURPOSE: To obtain a reinforcing fiber prevented from deterioration which is used as a titanium matrix compost material by forming diffusion-inhibited coatings consisting of a specified metal coating and an outer layer coating of the oxide of the same metal, on the surface of a ceramic fiber. CONSTITUTION: One metal from among the groups including yttrium, zirconium and hafnium is deposited on the surface of a silicon carbide base ceramic fiber to form a coating of the metal by plasma sputtering. The obtained coated fiber is subjected to heat treatment and the thermodynamically stable oxide of the same metal is formed as the outer layer to obtain the ceramic fiber having the diffusion-inhibited coatings consisting of two different kinds of coatings. When a fiber-reinforced metal composite material is produced by embedding this coated fiber in a titanium matrix, titanium and oxygen are absorbed by the diffusion-inhibited coatings to prevent the deterioration of the ceramic fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ceramic fibers set within a metal matrix, thereby creating a strong, lightweight composite structure.

The invention further includes metal matrix composites comprising ceramic fibers of the type described above.

The aerospace industry is constantly seeking materials that are lighter, yet at least as strong as materials known today. A step in this direction was, by way of example only, the adoption of titanium and titanium-based alloys. Light weight and strength were achieved, but at the expense and difficulty of processing due to the reaction of the material surface to ambient environmental conditions.

The next step is directed towards reducing the volume of lightweight metal per volume of the product structure, without loss of strength and preferably with increased strength, and for this purpose ceramic fibers are added to the removed metal parts. Substituted. An example of such a composite is silicon carbide fibers embedded in titanium.

However, as a result of the diffusion of titanium through the interface, the fibers deteriorated rapidly.

One attempt to combat the diffusion problem has been to provide silicon carbide fibers with a carbon-rich outer layer.

The diffusion of titanium into the fibers was slowed down.

One aspect of the present invention is to provide ceramic fibers with an improved coating that increases the resistance to diffusion of the matrix material in which the fibers are embedded.

According to one aspect of the invention, the ceramic fibers include a dual coating in which the inner coating is a thermodynamically stable oxide-producing metal and the outer coating is a stable oxide of the metal.

Further, the present invention includes a ceramic bifiber having a first inner coating of a metal that produces a thermodynamically stable oxide and a second outer coating that is a stable oxide of the metal.
A metal matrix composite structure is provided with a matrix of titanium or titanium alloy.

According to another aspect of the invention, a method for providing ceramic fibers with a diffusion coating includes wrapping the fibers with a metal in the group including yttrium, hafnium, and zirconium, and then applying an oxide of the metal to the metal coating. including the step of covering the

The invention will now be explained by way of example with reference to the accompanying drawings.

Please refer to FIG. Elongated silicon carbide fibers are disposed within the titanium 12 matrix.

The whole gives a composite structure in the form of lamellae.

Each of the fibers 10 has a support core 14 that can be constructed of tungsten or carbon.

Each fiber 10 is also encased in a double coating, the outer coating 16
is a metal that can form stable oxides under harsh conditions, especially at high temperatures. Outer coating 18 is a stable oxide of the metal.

The oxide coating 18 serves to prevent titanium from passing through the interface and ultimately diffusing into the ceramic fibers. Such diffusion, if it occurs, degrades the ceramic and, as a result, significantly shortens the service life of the composite structure of which it forms a part. It follows therefore that the oxide 18 must be of such a type that its ion formation results in inhibition to the ion formation of titanium. Therefore, the difference in charge between cations and the difference in ionic radius promote the diffusion process, so the self-diffusivity of cations must be low, and the ionic radius should be as close as possible to the ionic radius of the matrix material. Must be close to equal.

The following table exemplifies some metals which have suitable oxygen affinities and whose oxides have the required ionic properties mentioned above.

Summary of Thermodynamic and Diffusion Data Reference is now made to FIG. 1000″K to 1200
A graph was created from the results of calculations made on the amount of reaction that would take place between titanium and ittria over a period of 1000 hours at temperatures varied up to 0.degree.

Diffusion values are plotted as a function of coating thickness and it can be seen that the response over time increases significantly at higher temperatures. This has an effect on the manufacturing mode as described below. However, this graph also shows that if the thickness of the protective coating is at least 0.7μ, then at least 110μ
It also shows that up to 0'K, the reaction layer is kept at about 0.02μ.
This corresponds to the ittria coating 18 that covers the . A double advantage is obtained from using two coatings. One advantage is that the inner yttrium coating 16 is more flexible than the outer yttrium coating 18, thereby helping to absorb the degree of shock loading that occurs during use. The outer coating of Ittoria may be fragile. However, even if flaking does occur, a fresh coating of yttrium is exposed and oxidizes rapidly, effectively providing a self-healing coating.

Yttrium is plasma sputter coated onto the fibers. However, yttrium can be coated over yttrium in the same manner, or alternatively, the yttrium-coated fibers can be subjected to a conventional oxide-forming heat treatment, or the yttrium-coated fibers can simply be covered with a matrix material to coat the yttrium. is then allowed to absorb oxygen,
Apply itztrium on top of itztrium. Plasma sputtering is preferred because the stress generated can be controlled to a greater extent. That is, compressive stresses are generated in the sputtered coating, which counteract the tensile hoop stresses that may occur upon cooling if the coefficient of thermal expansion of the coating is different from that of the fibers.

A composite structure consisting of a titanium matrix material embedded with silicon carbide fibers coated with any of the above materials and their oxides as described above can be manufactured by any one of several methods. . For example, a thin plate of titanium may be placed between each pair of its cohesive surfaces with 10 elongated coated fibers.
Sandwich and overlap. The assembly is then enclosed in an inert atmosphere and exposed to pressure and temperature for an appropriate period of time to cause diffusion bonding of the titanium sheets. However, a disadvantage is that this method requires exposing the assembly to high temperatures for a period of hours. This may encourage excessive reaction between the titanium and the coating, as deduced from FIG.

Another method consists of injecting molten titanium into a mold containing an array of coated fibers 10, also under an inert atmosphere. High temperatures are also used, but the cooling period shortens the exposure time compared to that required when diffusion bonding is employed.

Another and preferred method is to lay a sheet of titanium on a copper heat sink (not shown), place the coated fibers 10 on top of the sheet, and roll the fibers 10 to the desired thickness. Vacuum plasma spray titanium onto this assembly so that it is covered.

The latter method is preferred since the vacuum plasma spraying of titanium powder onto the fibers while exposed to high temperatures takes place in milliseconds. This is not long enough to cause any harmful reactions.

The table below shows plasma spray parameters used to successfully wrap yttrium and yttria coated silicon carbide fibers with titanium matrix material.

Titanium plasma spray conditions Room pressure (argon): 175 mbar Gun current
Near 50A Plasma gas flow rate: Argon i/min Powder particle range: 45-63μ Gun-substrate distance: 330ff111 Powder supply amount: 20g/min He: 25! ! ,/min81
: 84! /min The arrangement of the ceramic fibers IO illustrated in FIG. 1 is not to be regarded as limiting.

The ceramic fibers IO can be arranged in a manner determined by the desired strength properties of the composite structure of the product. for example,
Ceramic fibers 10 can be arranged in multiple layers, each layer angled relative to the adjacent layer.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a composite structure comprising coated ceramic fibers according to the present invention, and FIG. 2 is a graph of interfacial diffusion depth versus coating thickness. 10...Fiber. 12...Titanium matrix. 14...Support core line. 16...Yttrium coating. 18...Outer layer coating.

Claims (1)

[Claims] 1. A ceramic having a double coating, in which the inner layer coating is a metal capable of producing a thermodynamically stable oxide, and the outer layer coating is the stable oxide of the metal. fiber. 2. The ceramic fiber of claim 1, wherein the metal is one of the group comprising yttrium, zirconium and hafnium. 3. The ceramic fiber according to claim 1 or 2, wherein the ceramic is silicon carbide. 4. A method of applying an anti-diffusion coating to ceramic fibers, comprising plasma sputtering a metal selected from the group comprising yttrium, zirconium and hafnium onto the ceramic fibers, and then encasing the metal with its oxide. 5. A method of applying a diffusion barrier coating to ceramic fibers according to claim 4, wherein said oxide is applied onto said metal by plasma sputtering said oxide in powder form. 6. The method of applying a diffusion prevention coating to ceramic fibers according to claim 4, wherein the oxide is generated from the metal by heat treating the metal-coated fiber. 7. Applying the anti-diffusion coating of claim 4 to the ceramic fibers, comprising the step of embedding the metal-coated ceramic fibers in a titanium matrix so that the outer surface of the metal can absorb titanium oxygen. Method. 8. Titanium or a titanium alloy encasing a plurality of elongated ceramic fibers each having an inner coating of a metal capable of forming a thermodynamically stable oxide and an outer coating of said oxide covering said metal. A composite structure containing a matrix of. 9. The composite structure of claim 8, wherein the ceramic fibers are silicon carbide fibers. 10. The composite structure according to claim 8 or 9, wherein the metal is one selected from the group comprising yttrium, zirconium and hafnium.