METHOD OF DIFFUSION BONDING

Abstract

A method of diffusion bonding two components together comprises providing a first component having a first bonding surface, and a second component having a second bonding surface. Each of the first bonding surface and the second bonding surface is etched. A cold working process is applied to each of the first bonding surface and the second bonding surface. Each of the first bonding surface and the second bonding surface is then etched. The first component is positioned adjacent to the second component with the first bonding surface abutting against the second bonding surface, to define a joint surface between the first component and the second component. A peripheral edge of the joint surface is sealed. The first bonding surface is diffusion bonded to the second bonding surface.

Claims

1. A method of diffusion bonding two components together, the method comprising the steps of: (a) providing a first component having a first bonding surface, and a second component having a second bonding surface; (b) applying a cold working process to at least one of the first bonding surface and the second bonding surface; (c) etching each of the first bonding surface and the second bonding surface; (d) position the first component adjacent to the second component with the first bonding surface abutting against the second bonding surface, to define a joint surface between the first component and the second component; (e) sealing a peripheral edge of the joint surface; and (f) diffusion bonding the first bonding surface to the second bonding surface.

2. The method as claimed in claim 1, wherein step (b) comprises the prior step of: (b) etching each of the first bonding surface and the second bonding surface.

3. The method as claimed in claim 1, wherein step (b) comprises the step of: (b1) applying a cold working process to each of the first bonding surface and the second bonding surface, to produce a cold worked layer having a depth from the surface of less than 1 mm.

4. The method as claimed in claim 3, wherein step (b1) comprises the step of: (b2) applying a cold working process to each of the first bonding surface and the second bonding surface, to produce a cold worked layer having a depth from the surface of less than 0.5 mm.

5. The method as claimed in claim 1, wherein step (b) comprises the prior step of: (b) applying a degreasing process to each of the first bonding surface and the second bonding surface.

6. The method as claimed in claim 1, wherein step (c) comprises the prior step of: (c) applying a degreasing process to each of the first bonding surface and the second bonding surface.

7. The method as claimed in claim 1, wherein step (a) comprises the subsequent step of: (a1) machining either or both of the first bonding surface and the second bonding surface, such that each of the first bonding surface and the second bonding surface has a surface finish of less than 0.8 m.

8. The method as claimed in claim 7, wherein the step (a1) comprises the subsequent steps of: (a1) inspecting each of the first bonding surface and the second bonding surface using a non-destructive evaluation technique; and (a1) quarantining either or both of the first component and the second component if a result of the non-destructive evaluation indicates the presence of a quantity and distribution of surface defects in excess of predetermined limits.

9. The method as claimed in claim 1, wherein the cold working process is selected from the group consisting of cold rolling, burnishing, peening and laser shock peening.

10. The method as claimed in claim 1, wherein the first component comprises a first tab portion extending distally from the peripheral edge of the joint surface, and the second component has a second tab portion extending distally from the peripheral edge of the joint surface, and step (e) comprises the step of: (e1) joining the first tab portion to the second tab portion around the periphery of the joint surface to seal the peripheral edge of the joint surface.

11. An aerofoil blade for a turbomachine formed by the method as claimed in claim 1, comprising a joint between a first component and a second component, wherein a grain structure across the joint comprises equiaxed grains having an average grain size of less than 80 m.

12. A gas turbine engine for an aircraft comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; and a gearbox that receives an input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, wherein at least one of the turbine and compressor comprises an aerofoil blade as claimed in claim 11.

13. The gas turbine engine according to claim 12, wherein: the turbine is a first turbine, the compressor is a first compressor, and the core shaft is a first core shaft; the engine core further comprises a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor; and the second turbine, second compressor, and second core shaft are arranged to rotate at a higher rotational speed than the first core shaft.

14. A computer program that, when read by a computer, causes performance of the method as claimed in claim 1.

15. A non-transitory computer readable storage medium comprising computer readable instructions that, when read by a computer, causes performance of the method as signal claimed in claim 1.

16. A signal comprising computer readable instructions that, when read by a computer, causes performance of the method as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0093] There now follows a description of an embodiment of the disclosure, by way of non-limiting example, with reference being made to the accompanying drawings in which:

[0094] FIG. 1 is a sectional side view of a gas turbine engine;

[0095] FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0096] FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

[0097] FIG. 4 shows a flowchart of the method of diffusion bonding two components together according to the present disclosure;

[0098] FIG. 5 shows a schematic sectional view of a diffusion bonding joint formed by a first aspect of the method of FIG. 4;

[0099] FIG. 6 shows a schematic sectional view of a diffusion bonding joint formed by a second aspect of the method of FIG. 4; and

[0100] FIG. 7 shows a schematic arrangement of the computer control of the method of FIG. 4.

[0101] It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION

[0102] FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

[0103] In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into the high pressure compressor 15 where further compression takes place. The compressed air exhausted from the high pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines 17, 19 before being exhausted through the nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

[0104] An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2. The low pressure turbine 19 (see FIG. 1) drives the shaft 26, which is coupled to a sun wheel, or sun gear, 28 of the epicyclic gear arrangement 30. Radially outwardly of the sun gear 28 and intermeshing therewith is a plurality of planet gears 32 that are coupled together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 to precess around the sun gear 28 in synchronicity whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via linkages 36 to the fan 23 in order to drive its rotation about the engine axis 9. Radially outwardly of the planet gears 32 and intermeshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

[0105] Note that the terms low pressure turbine and low pressure compressor as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan 23). In some literature, the low pressure turbine and low pressure compressor referred to herein may alternatively be known as the intermediate pressure turbine and intermediate pressure compressor. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

[0106] The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 3. Each of the sun gear 28, planet gears 32 and ring gear 38 comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in FIG. 3. There are four planet gears 32 illustrated, although it will be apparent to the skilled reader that more or fewer planet gears 32 may be provided within the scope of the claimed invention. Practical applications of a planetary epicyclic gearbox 30 generally comprise at least three planet gears 32.

[0107] The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft via linkages 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held fixed, with the ring (or annulus) gear 38 allowed to rotate. In such an arrangement the fan 23 is driven by the ring gear 38. By way of further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

[0108] It will be appreciated that the arrangement shown in FIGS. 2 and 3 is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of further example, the connections (such as the linkages 36, 40 in the FIG. 2 example) between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have any desired degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gearbox 30 has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in FIG. 2.

[0109] Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

[0110] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0111] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 20, 22 meaning that the flow through the bypass duct 22 has its own nozzle that is separate to and radially outside the core engine nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30.

[0112] The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

[0113] Referring to FIGS. 4 and 5, a method of diffusion bonding two components together is illustrated in the flow chart of FIG. 4, and a first embodiment of the diffusion bonded assembly 100 is shown in FIG. 5.

[0114] At step 50, a first component 100 has a first bonding surface 112, and a second component 120 has a second bonding surface 122.

[0115] The first and second bonding surfaces 112,122 may be planar. Alternatively, the first and second bonding surfaces 112,122 may be curved.

[0116] At step 51, each of the first bonding surface 112 and the second bonding surface 122 is machined to produce a smooth and flat surface having a surface finish of less than approximately 08 m. This machining operation ensures that the first bonding surface 112 and the second bonding surface 122 may be subsequently aligned prior to a diffusion bonding operation.

[0117] Following the machining operation, at step 52, each of the first bonding surface 112 and the second bonding surface 122 is inspected using a non-destructive evaluation (NDE) technique such as, for example, fluorescent dye penetrant inspection or eddy current inspection. This inspection is to identify any surface cracks or defects that might be increased in size by the subsequent cold working step.

[0118] The result of the non-destructive evaluation inspection is then used, at step 54, to quarantine the first component 110 and/or the second component 120 if any cracks or defects are found in excess of predetermined limits.

[0119] At step 56 the first bonding surface 112 and the second bonding surface 122 are degreased to remove any residual oils, cutting fluids or other contaminants prior to the etching step. This ensures that the etch process can be effective across the entirety of the first bonding surface 112 and the second bonding surface 122.

[0120] At step 58, each of the first bonding surface 112 and the second bonding surface 122 is etched to remove any oxide layer from the surface prior to the later diffusion bonding process step.

[0121] A cold working process is then applied to each of the first bonding surface 112 and the second bonding surface 122, at step 60.

[0122] Cold work is a process that results in an increased dislocation density in the material. This in turn inhibits the further movement of dislocations within the crystal structure. Dislocations also pile up at grain boundaries and prevent slip across the boundaries, which provides a further strengthening mechanism. The resistance to slip across the boundaries also reduces ductility and increases hardness, which is why too much cold work leads to cracking. Cold work also induces residual stress, which is the driver for recrystallization and grain growth.

[0123] The cold work process of step 60 is applied uniformly across the first bonding surface 112 to produce a first cold worked layer 114, and across the second bonding surface 122 to produce a second cold worked layer 124.

[0124] Uniform cold working can be produced by a number of alternative processes such as, for example, cold rolling, burnishing, peening, or laser shock peening. The localised nature of burnishing and laser shock peening are likely to make these methods more favourable. All cold work processes are likely to cause some distortion due to residual stresses, especially in thin sections. Therefore for thin sections some correction may be necessary by further either flattening or straightening to realign the joint. At this stage it may be advisable to carry out some form of NDE, for example ultrasonic inspection or eddy current of the joint. Cold working is likely to close any surface cracks so FPI would be ineffective.

[0125] At step 65, after being cold worked, the first bonding surface 112 and the second bonding surface 122 are further degreased to remove any residual oils, cutting fluids or other contaminants prior to the etching step. This ensures that the subsequent etch process can be effective across the first and second bonding surfaces 112,122.

[0126] At step 70, each of the first bonding surface 112 and the second bonding surface 122 is etched to remove any oxide layer from the surface prior to the diffusion bonding process step. A typical chemical etching process will remove less than 10 m from the bonding surface 112,122

[0127] At step 75, the first component 110 is positioned adjacent to the second component 120, with the first bonding surface 112 conformally abutting against the second bonding surface 122. The conformally positioned first and second bonding surfaces 112,122 together define a joint surface 130.

[0128] At step 80, a peripheral edge 132 of the joint surface 130 is sealed in readiness for the subsequent diffusion bonding process. The sealing of the peripheral edge 132 of the joint surface 130 is best achieved by a high localised energy input process such as, for example, laser welding, electron beam welding, or friction stir welding. This ensures that any heat input to the first and second components 110,120 generated by the joining process is minimal and so does not relieve the residual stress imparted by the earlier cold working process of step 60.

[0129] Alternatively the diffusion bonded assembly can be encapsulated in a metal canister, typically mild or stainless steel is used. This method is used for HIP diffusion bonding. The joint must be evacuated of any air prior to bonding and this is typically facilitated by welding a tube onto the joint, then pump and purge with an inert gas to remove the air from the assembly. The pipe is then heated and crimped to achieve a pressure weld.

[0130] At step 85, a diffusion bonding process is undertaken either by mechanically applying pressure, or hydrostatically applying pressure typically using high or low pressure argon. The joined first and second components 110,112 are then heated to a temperature at which the material is sufficiently plastic to allow creep deformation of the joint surface 130 to occur and for any surface asperities to collapse so that the first and second bonding surfaces 112,122 are in intimate contact. Diffusion and grain growth occurs across the joint surface 130, ideally resulting in an indistinguishable boundary with no discernible joint line.

[0131] The earlier cold work (step 60) will assist bonding by promoting recrystallization and grain growth due to the formation of sub-grain, which act as nucleation points for new grains during bonding, through the subsequent increase in grain boundaries and the increase in dislocations, both of which increase diffusion rates by up to an order of magnitude, i.e. grain boundaries and dislocations produce channels in which atoms can diffuse more easily. Dislocations and grain boundaries also accelerate the creep process, which is necessary in the initial phases of the diffusion bonding process. The key variable of the process are time, temperature and pressure; cold working should reduce the time required for diffusion and grain growth to occur by increasing the thermodynamic energy available for the process to take place.

[0132] Referring to FIG. 6, a diffusion bonded assembly according to a second embodiment of the method of the disclosure is designated generally by the reference numeral 200. Features of the assembly 200 which correspond to those of assembly 100 have been given corresponding reference numerals for ease of reference.

[0133] As described above in relation to the diffusion bonded assembly 100, the diffusion bonded assembly 200 has a first component 210 with a first bonding surface 212, and a second component 220 with a second bonding surface 222.

[0134] The first component 210 has a first tab portion 218 extending outwardly from a periphery of the first component 210 such that the first bonding surface 212 extends across the first tab portion 218. Likewise, the second component 220 has a second tab portion 228 extending outwardly from a periphery of the second component 220 such that the second bonding surface 222 extends across the second tab portion 228.

[0135] The method steps 51, 52, 54, 56, 58, 60, 65, 70, and 75 described above in relation to the first embodiment of the joint assembly 100 apply equally to the second embodiment of the joint assembly 200.

[0136] At step 80, it is the laterally protruding first and second tab portions 218,228 that are joined together to seal a peripheral edge of the joint surface 230. These first and second tab portions 218, 228 thus serve only to seal the peripheral edge of the joint surface 230 in preparation for the subsequent diffusion bonding process step. The use of the protruding first and second tab portions 218,228 ensures that the heat affected zone of the weld away from the joint surface 230 in order to prevent annealing of the cold worked layers 214,224 by the heat from the weld.

[0137] After the diffusion bonding process step (step 80) has been completed, the first and second tab portions 218,228 may be removed from the finished joint assembly 200 by, for example, machining.

[0138] The method of the present disclosure may be controlled by means of a computer as illustrated in FIG. 7. A computer 170 is connected the diffusion bonding apparatus 160 by means of a signal line 176. The computer 170 includes a computer program 172 that is stored a computer readable storage medium 174. The operating instructions for the diffusion bonding apparatus may be stored on or transmitted over, as one or more instructions or code, a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media, which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

[0139] By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transient media, but are instead directed to non-transient, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0140] Instructions may be executed by one or more processors, such as one or more DSPs, general purpose microprocessors, ASICs, FPGAs, or other equivalent integrated or discrete logic circuitry. Accordingly, the term processor, as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0141] The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a processor, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

[0142] Various examples have been described. These and other examples are within the scope of the following claims.

[0143] Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

[0144] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Moreover, in determining extent of protection, due account shall be taken of any element which is equivalent to an element specified in the claims. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.