GB2283042A

GB2283042A - Method for fabricating long-fibre-reinforced components, e.g. turbine blades

Info

Publication number: GB2283042A
Application number: GB9421132A
Authority: GB
Inventors: Rolf Leucht; Klaus Weber
Original assignee: Deutsche Forschungs und Versuchsanstalt fuer Luft und Raumfahrt eV DFVLR
Current assignee: Deutsches Zentrum fuer Luft und Raumfahrt eV
Priority date: 1993-10-19
Filing date: 1994-10-19
Publication date: 1995-04-26
Anticipated expiration: 2014-10-19
Also published as: FR2711330A1; GB9421132D0; DE4335557C1; GB2283042B; FR2711330B1

Description

1 METHOD FOR FABRICATING LONG-FIBRE-REINFORCED COMPONENTS The present

invention relates to a method for fabricating long-fibre- reinforced components, particularly components made of a brittle or ductile material, i.e. a matrix material deformable at high temperatures (about 5000C to 2000OC) and at high pressures (at about 1000 bar and more), and reinforced with high-tensile and high- temperature- res i stant fibres of brittle material which is sensitive to radial shear forces. The matrix material can be a metal or a metal alloy, which may be titanium based.

To give higher strength and stability to components, and to reduce their weight it is principally known to embed fibres into the components. Depending on the fibre material selected, thermal expansion of the component is also decreased and the high temperature resistance of the thus fibre-reinforced component is increased. Advantageously, the fibrereinforcing material consists of fibres coated with a matrix material. This is advantageous in that adjacent fibres do not contact each other but are rather enclosed by a material, namely the matrix material. Preferably, titanium based alloys are used as the matrix material, while the fibre itself is made of silicon carbide (SiC).

2283042 9 2 In the context of this invention, the term "fibre" means a mono-fibre whose interior is made of f ibre material and whose exterior is coated with matrix material. The fibre material in the interior can itself comprise a central core with one or more surrounding protective layers onto which the matrix material is deposited. In the case of a SiC fibre, the core can consist of carbon, a fibre material of SiC enclosing the core, another protective layer substantially of carbon, and the matrix material of a titanium-based alloy.

DE 40 21 547 A1 discloses a method for fabricating fibre-reinforced components wherein a carrier body is wound with at least one fibre coated with a matrix material and this wound body is subsequently exposed to a hot isostatic pressing process. In the hot isostatic pressing process, the wound body is encapsulated, i.e. enclosed by a capsule, subsequently, the capsule is evacuated and closed vacuum-tight, and thereafter, this capsule is heated and subjected to high pressure from all sides. With the known process, however, only fibrereinforced components with wound fibrereinforcement can be manufactured. It is, however, often desirable for the fibre-reinforced component to be of high stability in one dimension. This, for example, is the case with turbine blades which are, particularly in the radial direction of the turbine, subject to extreme stress.

3 DE 29 15 412 C2 discloses a method for manufacturing a body of fibrereinforced metal (matrix) material. The individual fibres are introduced into tubes representing the matrix material. Several of such tubes are inserted into an envelope-like body which already corresponds to the contour of the component to be manufactured. The body, which is open at the two end faces thereof is closed by stoppers of suitable material, whereupon the thus closed body is subjected to a hot isostatic pressing process. Subsequently, the stoppers are removed or the ends of the body are worked otherwise. The hot isostatic pressing of the body necessitates an air-tight sealing at its ends which is technically troublesome, since conditions at the ends of the body change during the hot isostatic pressing process during which a compaction takes place.

Another method for fabricating fibre-reinforced composite materials is known from DE 37 00 805 C2. Also in this known method, the fibres are inserted into a hollow body which already corresponds to the contour of the component to be fabricated. The document is silent about a gas-tight sealing of the ends of the hollow mould. It is only said that the fibres and the powder matrix introduced therebetween are compacted to such a high degree that the powder particles are welded to each other as well as the fibres.

4 It is an object of the present invention to provide an improved method for fabricating long-fibrereinforced components.

According to the invention there is provided a method for fabricating long- f ibre- re inf orced components comprising a matrix material with embedded, substantially parallel long fibres coated with matrix material, the method comprising the steps of:

a workpiece particularly of matrix material with at least one cavity being open at least at one side and having a smaller cross section than the component to be fabricated, filling the cavity with long fibres coated with matrix material with the individual long fibres being substantially arranged in parallel to each other, subjecting the workpiece with the long fibres located in the cavity thereof to encapsulation and a hot isostatic pressing process, and thereafter working the workpiece to produce the outer contour of the long- fibrereinforced component.

In accordance with the invention the fibre reinforcement is in form of individual, substantially parallel long fibres and the fabrication process is easy to perform.

The starting point of the method according to the invention is a workpiece, preferably of matrix material, i.e. the coating material of the long fibres. The workpiece possesses a cavity which is open at least at one side and substantially corresponds to the form of the component to be fabricated and has a smaller cross section than the latter. The cavity is tightly filled with individual coated long fibres, the individual fibres being arranged substantially in parallel in the cavity. The thus prepared workpiece is subjected to a hot isostatic pressing process in which the workipiece is initially encapsulated in a container which is evacuated and closed vacuum-tight. The container is heated up to high temperatures and subjected to a high pressure from all sides, so that the ductility point of the matrix material is reached and, if necessary, exceeded. After the hot isostatic pressing process, the workpiece is removed from the container and then worked in order to fabricate the desired component.

Preferably, the container is evacuated at elevated temperatures to outgas the surface of the fibres coated with matrix material and/or of the workpiece. These surfaces can be chemically contaminated, e.g. by adhesive, oxygen and/or hydrogen. Adhesive, e.g., can be used to retain the long fibres at the inner walls of the cavity upon equipping the workpiece.

The component fabricated according to the method of the present invention is fibre-reinforced in one dimension'. - The method is particularly advantageous for manufacturing fibre-reinforced turbine blades, which are 6 exposed to extreme stress, particularly in radial direction of the turbine. Silicon carbide fibres coated with a titanium-based alloy are particularly suitable long fibres. The increased temperature resistance of the turbine blades fabricated according to the method of the invention makes it possible to do without cooling of the turbine blades up to the mid operational temperature range of the turbine. In any case less cooling is needed than with the conventional turbine blades.

As to the method according to the invention, it can be generally said that the cavity in the workpiece is configured and dimensioned such that the finished workpiece encloses the cavity - then filled with long fibres and matrix material - i.e. comprises an envelope or sheath enclosing the fibre-reinforced region. This means that the cavity needs to be correspondingly dimensioned to that of the component.

Principally, the workpiece comprising the cavity can be formed integrally, but can also comprise several parts, particularly two parts. The two or more parts of the workpiece are then fitted together upon filling the cavity, forming the space to be filled with long fibre material therebetween.

According to the method of the invention, also partially fibre-reinforced components can be manufactured. For example, several cavities may be formed in the workpiece, the finished components 7 enclosing all of the cavities. It is also possible that the one or more cavities are equipped with one or several cores, respectively, preferably of matrix material, in order to fill only the remaining "annular space" with long fibres. Further, the core material can be removed again after the hot isostatic pressing to provide an inner cooling chamber for a turbine blade fabricated according to the method of the invention.

To increase the degree of filling with long fibre material with respect to the workpiece cavity which is open at least at one side, the workpiece is suitably vibrated when introducing the long fibre material. if necessary, the matrix material can additionally be compacted with powder of the matrix material. Therefore, powder of a particle size of 10 pm to 20 pm is suitably used.

Advantageously, contaminants are removed from the workpiece before the long fibres are introduced. This is preferably done by etching the workpiece and the cavity walls.

When a workpiece equipped with parallel long fibres is subjected to a hot isostatic pressing process, the long fibres, in the middle thereof, are compacted to a higher degree than towards their ends where they are adjacent to the capsule enclosing the workpiece. This is caused -by the fact that the radial pressure acting upon the long f ibres is lower at the ends of the long fibres due to the capsule wall. This means that the long fibres slightly diverge at their ends. This effect called "edge effect" hereinafter can advantageously be prevented in the isostatic pressing process by providing the ends of the long fibres introduced into the cavity with matrix material. Thus, the long fibres do no longer extend directly up to the capsule wall, but are spaced therefrom by a layer of matrix material. Advantageously, the cavity in the workpiece is closed by plates or the like of matrix material.

Preferably, the cavity in the workpiece is relieved by electrical erosion, but also "pressed" workpieces can be used in which the cavity is f ormed after removal of a core around which the material of the workpiece has been pressed. Basically, also other working methods for producing or relieving the cavity therein are possible.

Hereinafter, an embodiment of the invention is explained in detail with respect to the drawings. In the drawings, Figures 1 to 5 show the different stages for fabricating a long- f ibre-reinf orced turbine blade from a titanium-based alloy with silicon carbide long fibres.

As shown in Figure 1 the starting point is a substantially cuboid workpiece block 10 of a titaniumbased alloy. In this workpiece block 10 shown in Figure 2, a continuous cavity 16 is relieved by electrical erosion, which is open at two sides, i.e. at the upper t 9 surf ace 12 and at the lower surf ace 14, and whose cross section corresponds to the desired blade geometry and is smaller than the turbine blades to be manufactured. After the cavity 16 has been finished, the workpiece block 10 is etched to clean the cavity inner faces. Subsequently, as shown in Figure 3, the cavity 16 is filled with silicon carbide fibres 18 which comprise a coating, e.g. of the same material as the workpiece block 10. The fibres 18 are long fibres extending over the entire height of the workpiece block 10 between the upper and lower surfaces 12,14 thereof. As indicated in Figure 3 the long fibres are accommodated in parallel relative to each other in the cavity 16. The degree of filling of the cavity 16 with long f ibres 18 is increased by vibrating the workpiece block 10 during the filling. Additionally, titanium-based alloy powder of a particle size of about 10 pm to 20 lim can be introduced into the cavity 16 for compacting.

Subsequently, the thus prepared workpiece block 10 is exposed to a hot isostatic pressing process. Therefore, the upper and lower surfaces 12,14 of the workpiece block 10 are initially covered with metal sheets 20, as shown in Figure 4 consisting of the same titanium-based alloy as the workpiece block 10 and the coating of the long fibres 18. The workpiece block 10 thus covered at the open sides of its cavity 16 is then encapsulated by inserting it into a V2A-steel container.

This container 22 is evacuated to about 10-7 mbar at temperatures of about 5000C and closed vacuum tight thereafter. Subsequently, the actual hot isostatic pressing process is performed, in which, by means of temperature and pressure effects from all sides, the ductility point of the matrix material, i.e. the titanium-based alloy, is reached and advantageously exceeded. After the hot isostatic pressing process, the workpiece block 10 is worked by, e.g., a WC-machine, to get the geometry of the turbine blade 24 according to Figure 5. This turbine blade 24 is characterised by a sheath 26 of matrix material and a fibre-reinforced core 28 consisting of the parallel long fibres embedded in the matrix material. An integral part of the turbine blade 24 is a base 30 intended for mounting the turbine blade 24 to the turbine shaft. The long fibres 18 extend into the base 30. Like the blade geometry, the base 30 is also obtained by the CNC-machine working the hot isostatically pressed workpiece.

0 f 11

Claims

1. A method for fabricating long-fibre-reinforced components comprising a matrix material with embedded, substantially parallel long fibres coated with matrix material, the method comprising the steps of: a workpiece (10), particularly of matrix material with at least one cavity (16) being open at least at one side and having a smaller cross section than the component (24) to be fabricated, filling the cavity (16) with long fibres (18) coated with matrix material with the individual long fibres (18) being substantially arranged in parallel to each other, subjecting the workpiece (10) with the long fibres (18) located in the cavity (16) thereof to encapsulation and a hot isostatic pressing process, and thereafter working the workpiece (10) to produce the outer contour of the long-fibre-reinforced component (24).

2. The method according to claim 1, characterised in that the workpiece (10) is vibrated on introduction of long fibres (18) into the at least one cavity (16).

3. The method according to claim 1 or 2, characterised in that a powder of matrix material is additionally introduced into the at least one cavity (16) of the workpiece (10).

4. The method according to claims 1 to 3, 12 characterised in that the workpiece (10) is etched before the long fibres (18) are introduced into the at least one cavity (16).

5. The method according to one of claims 1 to 4, characterised in that at least one core, particularly of matrix material, is inserted into the at least one cavity (16), the at least one core having a smaller cross section than the at least one cavity (16) and the remaining space being filled with long fibres (18).

6. The method according to claims 1 to 5, characterised in that the workpiece (10) is provided with matrix material (20) on its at least one side (12;14) open to the cavity (16) for covering the ends of the long fibres (18) before the hot isostatic pressing process is performed.

7. The method according to claims 1 to 6, characterised in that the cavity (16) in the workpiece (10) is relieved, particularly by electrical erosion.

8. The method according to claims 1 to 7, characterised in that the workpiece (10) has a one-piece or a multi-part configuration.

9. Use of a method according to one of claims 1 to 7 for fabricating a (24).

10. A method of fabricating a component substantially as described with reference to and as illustrated in the accompanying drawings.

long-fibre-reinforced turbine blade il 1 13

11. A component produced by a method according to one of claims 1 to 10.