GB2258182A

GB2258182A - Method of joining together at least two metallic surfaces by diffusion bonding and apparatus for use therein.

Info

Publication number: GB2258182A
Application number: GB9116414A
Authority: GB
Inventors: Stewart Williams
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1991-07-30
Filing date: 1991-07-30
Publication date: 1993-02-03
Anticipated expiration: 2011-07-30
Also published as: GB9116414D0; GB2258182B

Abstract

Prior to joining together two metallic surfaces 1 by diffusion bonding each surface 1 is subjected to a beam 2 of laser radiation operative to clean at least part of the surface 1 of surface contamination. Preferably the laser radiation is produced by an ultra-violet excimer laser source 3 or by a metal vapour laser operating in the visible wavelength range. The surface 1 may be moved relative to the beam 2 of laser radiation by a multiple axis work station 8 or the beam 2 may be moved relative to the surface 1 by a movable fibre optic system. <IMAGE>

Description

METHOD OF JOINING TOGETHER AT LEAST TWO METALLIC SURFACES BY DIFFUSION BONDING AND APPARATUS FOR USE THEREIN This invention relates to a method of joining together at least two metallic surfaces by diffusion bonding and to apparatus for use therein.

Diffusion bonding of metals and metallic materials is an important technique for the joining together of metallic or metal surfaces, particularly prior to superplastic forming. Whilst diffusion bonding joining is successful for some metal and metallic materials, such as titanium alloys, it is not so suitable for joining other materials such as aluminium alloys. This basically is due to the presence of surface contamination, such as oxide layers, on the surfaces to be joined.

Conventionally such surface contamination, i.e. oxide layers, has been removed by techniques which usually involve a degree of mechanical treatment, such as shot blasting, combined with a wet chemical treatment and possibly followed by deposition of a further metal on the cleaned surface to provide resistance to further contamination. These conventional techniques have achieved limited success and can involve further undesirable limitations such as the length of time required for the surface contamination removal treatment. Additionally such conventional techniques are generally slow and expensive and may require the contamination removal treatment to be carried out in vacuo such as is necessary for ion beam milling.

There is thus a need for a generally improved method of joining together at least two metallic surfaces by diffusion bonding which is more generally applicable to different metal and metallic surfaces and which involves a surface contamination removal step.

According to one aspect of the present invention there is provided a method of joining together at least two metallic surfaces by diffusion bonding, including the steps of subjecting each of the surfaces to be joined together to a beam of laser radiation operative at least to clean at least part of the surfaces to be joined of surface contamination, and joining said cleaned surfaces together by diffusion bonding.

Preferably the beam of laser radiation used is a beam of ultra-violet radiation supplied by an excimer laser.

Conveniently the ultra-violet radiation has a wavelength in the range of 150-400 nanometres (nm), a pulse energy of up to 10 Joules (J), a pulse duration in the range from 1 nanosecond (ns) to 10 microseconds (,us) and a repetition rate of up to 10 kiloHertz (kHz).

Advantageously the laser radiation is incident on the surface to be joined with a fluence in the range of from 0.10 to 200 Joules per centimetre squared (Jlcm2) Preferably the laser radiation has a wavelength of substantially 248nm or a substantially 308nm, a pulse energy of substantially 0.5J, a pulse duration of substantially 30ns and a repetition rate of substantially 200Hz.

Conveniently the laser radiation is incident on the surface to be joined with a fluence in the range of from 0.10 to 30 J!cm2.

Advantageously the metallic surfaces to be joined are made of aluminium or an aluminium containing alloy and the surface contamination is one or more oxides.

Alternatively the beam of laser radiation used is a beam of radiation in the visible wavelength range supplied by a metal vapour laser, the metallic surfaces to be joined are made of copper or of a copper containing alloy, and the surface contamination is one or more oxides.

Preferably the laser is operated in a pulsed manner.

Conveniently the area of said at least one metallic surface treated is given any desired lateral shape such that diffusion bonding takes place only in the shaped area.

Conveniently the desired laterally shaped area is produced by imaging a mask onto the surface being subjected to laser radiation or by moving one or more of the surfaces being subjected to laser radiation and the beam of laser radiation relative to the other.

According to another aspect of the present invention there is provided apparatus for use in the foregoing method for cleaning by laser radiation a metallic surface to be joined, including a source of a beam of laser radiation, means for delivering the laser radiation beam to a surface to be joined and means for moving one of the surface and laser radiation beam relative to the other.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying single figure drawing in which Figure 1 shows in diagrammatic block form apparatus for cleaning a surface to be joined for use in one embodiment of the method of the present application.

The method of the present invention for joining together at least two metallic surfaces 1 by diffusion bonding includes a step of cleaning at least one surface 1 by a beam of laser radiation 2 to remove surface contamination. The surfaces 1 are then joined together by diffusion bonding in any convenient manner. In the illustrated example the beam 2 or laser radiation used is a beam of ultra-violet radiation supplied by an excimer laser source 3.

The excimer laser source 3 is particularly useful for treating metallic surfaces 1 made of aluminium or an aluminium containing alloy in which the surface contamination is one or more oxides.

Alternatively, and not illustrated, the laser source 3 may be a metal vapour laser providing a beam of laser radiation in the visible wavelength range. This latter alternative is particularly suitable for treating metallic surfaces made of copper or a copper containing alloy having a surface contamination made up of one or more oxide layers.

When the laser source 3 is an excimer laser as shown in Figure 1 the ultra-violet radiation preferably has a wavelength in the range of from 150 to 400 nanometres (nm) a pulse energy of up to 10 Joules (J) a pulse duration in the range of from 1 nanosecond (ns) to 10 microseconds (cos) and a repetition rate of up to 10 kiloHertz (kH). Such ultra-violet light given out by the excimer laser source 3 in the form of a beam of laser radiation 2 is passed through means for delivering the laser radiation beam to the surface 1. In the example illustrated in Figure 1 the means for delivering the beam 2 is an optical system including a field lens 4 located nearest to the laser source 3, an imaging lens 5 located nearest to the surface 1 and an aperture or mask 6 containing an opening 7 therethrough located between the field lens 4 and the imaging lens 5.A suitable excimer laser source 3 produces ultra-violet radiation with a wavelength of substantially 248nm or substantially 308nm, at a pulse energy of substantially 0.5J, a pulse duration of substantially 30ns and a repetition rate of substantially 200Hz.

The optical system transfers the beam 2 of laser radiation to the surface 1 so that it is incident with a fluence in the range of from 0.10 to 200J/cm2, preferably in the range of from 0.10 to 30 J/cm2.

The laser source 3 preferably is operated in a pulsed manner. By varying the laser parameters such as fluence, flux, wavelength, number of pulses, it is possible to control surface topography.

Additionally the area of the surface 1 treated can be given any desired lateral shape such that diffusion bonding takes place only in the shaped area. This may be done by imaging a mask onto the surface 1 or by moving one or more of the surface 1 and the beam 2 relative to each other. Because the laser beam 2 can be used to clean and treat the surface 1 in a highly defined manner it is possible to pattern the surface 1 so that bonding only occurs in the patterned areas. This is particularly important for sup erplas tic forming applications where the surface areas which are not to be joined by diffusion bonding are covered in a different material, such as ceramic, which requires another stage of processing. Means are provided for moving one of the surface 1 and laser radiation beam 2 relative to the other.

In the example of Figure 1 such means takes the form of a multiple axis work station operable, under the control of a computer 9, to grip the surface 1 and move it about, particularly, in one plane transverse to the beam 2. The computer 9 also ensures that the desired areas of the surface 1 are exposed to the required number of laser radiation beam pulses.

As an alternative, not illustrated, the optical system made up of the lens 4, mask 6 and lens 5 could be replaced by a fibre optic delivery system and the multiple axis work station 8 could be replaced by a robot arm operable to move the fibre optic delivery system. Thus in this alternative the surface 1 is held static whilst the radiation beam 2 is moved relative to the surface 1 by means of movement of the fibre optic delivery system.

Claims

1. A method of joining together at least two metallic surfaces by diffusion bonding, including the steps of subjecting at least one of the surfaces to be joined together to a beam of laser radiation operative at least to clean at least part of the surfaces to be joined of surface contamination, and joining said cleaned surfaces together by diffusion bonding.

2. A method according to claim 1, in which the beam of laser radiation used is a beam of ultra-violet radiation supplied by an excimer laser.

3. A method according to claim 2, in which the ultra-violet radiation has a wavelength in the range from 150 to 400 nanometres (nm), a pulse energy of up to 10 Joules (J), a pulse duration in the range of from 1 nanosecond (ns) to 10 microseconds (ills) and a repetition rate of up to 10 kiloHertz (kHz) .

4. A method according to claim 3, in which the laser radiation is incident on the surface to be joined with a fluence in the range of from 0.10 to 200 Joules per centimetre squared (J/cm2).

5. A method according to claim 3 or claim 4, in which the laser radiation has a wavelength of substantially 248nm or of substantially 308nm, a pulse energy of substantially 0. SJ, a pulse duration of substantially 30ns and a repetition rate of substantially 200Hz.

6. A method according to claim 5, in which the laser radiation is incident on the surface to be joined with a fluence in the range of from 0.10 to 305/cm2

7. A method according to any one of claims 1 to 6, in which the metallic surfaces to be joined are made of aluminium or an aluminium containing alloy and in which the surface contamination is one or more oxides.

8. A method according to claim 1, in which the beam of laser radiation used is a beam of radiation in the visible wavelength range supplied by a metal vapour laser, in which the metallic surfaces to be joined are made of copper or of a copper containing alloy and in which the surface contamination is one or more oxides.

9. A method according to any one of claims 3 to 8, in which the laser is operated in a pulsed manner.

10. A method according to claim 9, in which the area of said at least one metallic surface treated is given any desired lateral shape such that diffusion bonding takes place only in the shaped area.

11. A method according to claim 10, in which the desired laterally shaped area is produced by imaging a mask onto the surface being subjected to laser radiation or by moving one or more of the surface being subjected to laser radiation and the beam of laser radiation relative to the other.

12. A method according to claim 11, in which the surface being subjected to laser radiation is moved relative to the beam of laser radiation.

13. A method of joining together at least two metallic surfaces by diffusion bonding, substantially as hereinbefore described with reference to the accompanying drawing.

14. Apparatus for use in the method according to claim 1 for cleaning by laser radiation a metallic surface to be joined, including a source of a beam of laser radiation, means for delivering the laser radiation beam to a surface to be joined and means for moving one of the surface and laser radiation beam relative to the other.

15. Apparatus according to claim 14, wherein the laser radiation source is an ultra-violet excimer laser or a metal vapour laser with radiation in the visible wavelength range.

16. Apparatus according to claim 14, wherein the means for delivering the laser radiation beam is an optical system including a field lens located nearest to the laser source, an imaging lens located nearest to the surface to be joined and an aperture or mask located between the field lens and imaging lens.

17. Apparatus according to claim 14, wherein the means for delivering the laser radiation beam is a fibre optic system.

18. Apparatus according to claim 14, wherein the means for moving one of the surface and laser radiation beam relative to the other is a computer controllable multiple axis work station for supporting the surface and moving it relative to the laser radiation beam.

19. Apparatus according to claims 17, wherein the means for moving one of the surface and laser radiation beam relative to the other is a robot arm system operable to move the fibre optic system and hence the laser radiation beam, relative to the surface.

20. Apparatus for cleaning by laser radiation a metallic surface to be joined, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawing.