GB2618130A

GB2618130A - Multi-material joint

Info

Publication number: GB2618130A
Application number: GB2206231.9A
Authority: GB
Inventors: Xu Xiangfang
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2022-04-28
Filing date: 2022-04-28
Publication date: 2023-11-01
Also published as: GB202206231D0; WO2023208730A1

Abstract

A multimaterial component (figure 3) (e.g. an aircraft pylon) may have a nickel-based superalloy member at one end; a titanium alloy member at the other end; and a transition member 50 therebetween, to aid joining of the Ti & Ni members. The transition member 50 may comprise a layer 52 of aged Inconel (RTM) 718 or nickel; and a layer 54 containing titanium. The transition layers 52, 54 may be joined together via explosion welding, linear friction welding, or rotary friction welding. A tantalum or BAu4 (Goldbraze 8218) thin film diffusion barrier 56 may help prevent or reduce diffusion of material between the layers 52, 54. A transition member may comprise VC nanoparticles; a V/Cu bilayer; tantalum; or Goldbraze 8218. A member may comprise a lattice, or channels with a fluid coolant, to cool and reduce thermal transfer (figure 4). Lateral motion constraints (brackets) may reduce shear stress (figure 5).

Description

Intellectual Property Office Application No GI3220623 1 9 RTM Date:27 October 2022 The following terms are registered trade marks and should be read as such wherever they occur in this document: Inconel Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo

MULTI-MATERIAL JOINT

TECHNICAL FIELD

[0001] The present invention relates to multi-material components formed of two different materials; and ways of constructing multi-material components. Such components are particularly suitable for use in aircraft.

BACKGROUND

[0002] When designing components for use in hot areas, materials must be selected with a view to maintaining appropriate strength even after long exposure to high temperatures. An example or such an application is illustrated in Figure 1. An aircraft 1 has engines 2 which generate significant amounts of heat. These engines 2 are connected to the aircraft (typically the wings 3) by means of a pylon 4, which becomes hot in use due to the heat generated by the engines (2).

[0003] Materials used in aircraft construction are normally chosen to minimise their weight, thereby improving the fuel economy of the aircraft. However such materials are not always suitable for use at high temperatures. Areas of the aircraft subject to such temperatures lead to the use of thermally stable materials such as Inconel, which maintains high strength at high temperatures. Although very suitable for use at high temperatures, such materials tend to be significantly denser and more expensive than materials used throughout the rest of the aircraft. As such, considerable time and effort is placed into the design of structures and systems made from multiple materials, in order to provide for a high performance, low weight, thermally sale structure/system.

[0004] With reference to Figure 2 an example multi-material structure 10 is shown. It comprises a first member 12 formed of Inconel, for coupling to the engine, and a second member 14 formed of Titanium for coupling to the wing 3 of the aircraft. The first and second members 12, 14 are coupled together by means of brackets 16 secured to the first and second member 12, 14 by bolts 18. Unfortunately whilst the structurel0 is lighter and cheaper than a monolithic structure made from a material suitable for the thermal load, it has both a high part count and significant assembly costs.

[COOS] One potential solution to die high part count and high assembly costs is to create monolithic components comprising multiple materials. However such multi-material components face two significant challenges. Firstly, dissimilar materials may have differing coefficients of thermal expansion. In the context of significant thermal loads, this presents a serious challenge to overcome. Secondly, dissimilar materials may not bond well to each other, for example forming brittle intermetallic compounds that reduce the strength of the eventual component.

[0006] Accordingly it is desirable to provide a multi-material component that avoids the need for bolting but mitigates the challenges of thermal expansion and/or impaired bonding.

SUMMARY

[0007] According to a first aspect of the present disclosure, there is provided a method of creating a multi-material component, the method comprising: a step of making a transition member comprising a first transition layer and a second transition layer, the making being carried out by: providing a first transition blank formed of a material selected from the group consisting of aged Inconel 718 and pure Nickel; providing a second transition blank formed of Titanium; and welding the first transition blank and the second transition blank together via a method selected from the group consisting of explosion welding, linear friction welding and rotary friction welding, the first transition blank and second transition blanks respectively forming the first transition layer and the second transition layer; a step of making a first member of a Nickel based superalloy; a step of making a second member of Titanium; and a step of joining the transition member between the first member and second member, the first transition layer being joined to the first member and the second transition layer being joined to the second member, such that the transition member securely joins together the first member and the second member.

[0008] Such a method provides a way to join the first. and second member together with a strong connection that is resilient to heat despite the dissimilar materials and avoids the need for any fasteners.

[0009] Optionally, the method further comprises a step of shaping the transition member before the step of joining the transition member between the first member and the second member. This may allow the transition member to be shaped such that any stress Is encountered in directions in which the transition member is strongest.

[0010] Preferably, the method further comprises a step of providing a diffusion barrier blank and wherein the step of welding the first transition blank and second transition blank together comprises welding the diffusion barrier blank in between the first. transition blank and second transition blank. This provides a diffusion bather between the first transition layer and second transition layer which may improve the longevity of the strength of the transition member.

[0011] Preferably, the diffusion barrier blank is provided on the surface of one of the first transition blank and second transition blank. This simplifies the welding process.

[0012] Advantageously, the diffusion barrier blank comprises Tantalum. Tantalum has a high melting point and acts as an excellent diffusion bather.

[0013] Preferably, the step of joining the transition member between the first member and second member comprises making by additive manufacturing at least one of the first. member and second member on the transition member. This provides a good connection between the transition member and at least one of the first member and second member whilst avoiding excessive heat or waste.

[0014] Optionally, the step of making the first member of a Nickel based superalloy comprises a step of making a lattice in the first member, the lattice having a lower thermal conductivity than the rest. of the first member for reducing the rate of thermal transfer through the first member to the second member. This may increase the permissible operating temperature of the first member.

[0015] Optionally, the method further comprising a step of making channels through the first member for receiving cooling fluid to cool the first member. This may also increase the permissible operating temperature of the first member.

[0016] Preferably, the steps of making the first and second member and the step of joining is carried out via a process of additive manufacture upon the transition member. This minimizes the disturbance to the transition member caused by the joining.

[0017] Optionally, the method may comprise a further step of machining the multi-material component to obtain a desired shape.

[0018] Advantageously, the method Further comprises a step of providing lateral motion constraints around the transition member for mitigating shear stress in the multi-material component. This may improve the longevity of the multi-material component.

[0019] According to a second aspect of the present disclosure, there is provided a multi-material component comprising: a first member formed of a first material; a second member formed of a second material, and a transition member; situated and joined between the first. member and the second member; wherein the first material is a Nickel based superalloy; the second material is Titanium; and the transition member comprises a first. transition layer joined to the first member and a second transition layer joined to the second member; the first transition layer comprising a material selected from the group comprising aged Inconel 718 and pure Nickel, the second transition layer comprising Titanium.

[00201 Such a component is a monolithic replacement for previous bolted components.

[0021] Preferably, the transition member further comprises a diffusion barrier between the first transition layer and the second transition layer. This may extend the life of the component by inhibiting diffusion between the first and second transition layers.

[0022] Advantageously, the diffusion banier comprises a layer of Tantalum. This high melting point material may provide a good barrier. Alternatively, B Au-4 may also be suitable.

[0023] Optionally, the second transition layer comprises a material selected from the group consisting of Titanium 64 and pure Titanium.

[00241 Preferably, the multi-material component further comprises a lattice in the first member for reducing the rate of thermal transfer through the first member to the second member. This may increase the maximum permissible operating temperature of the first member.

[00251 Advantageously, the multi-material component may further comprise channels through the lirst member For receiving cooling fluid to cool the first member. This again may increase the temperature at which the first member may be used.

[0026] Advantageously, an aircraft may comprise the multi-material component. The component is particularly suitable for use near heat. sources like the engines of the aircraft.

[0027] Advantageously, the aircraft may also comprise lateral motion constraints around the transition member for mitigating shear stress in the multi-material component. This may increase the longevity of the multi-material component.

[0028] According to a third aspect or the present disclosure, there Is provided a transition member for joining to a first member formed of Inconel and a second member formed of Titanium, the transition member having been obtained by a process of welding and being comprising a first transition layer for joining to the first member comprising a material selected from the group comprising aged Inconel 718 and pure Nickel and a second transition layer for joining to the second member comprising a material selected form the group comprising Tiumium 64 and pure Titanium.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Embodiments of thc invention will now bc described, by way of example only, with reference to the accompanying drawings, in which: [0030] Figure 1 is an aircraft; [0031] Figure 2 is a schematic cross section view of a bolted multi-material structure; [0032] Figure 3 is a schematic cross section view of a multi-material component

according to an embodiment of the disclosure;

[0033] Figure 4 is a schematic cross section view of a multi-material component according to a further embodiment of the disclosure; [0034] Figure 5 is a schematic cross section view of a multi-material component with lateral motion constraints in use; [0035] Figure 6 is a schematic cross section view of a multi-material component with a bilayer transition member, and [0036] Figure 7 is a schematic cross section view of a transition member according to

an embodiment of the disclosure.

DETAILED DESCRIPTION

[0037] As previously described, pylons for use on aircraft. 1 to support an engine 2 (or other heat source) on part of the aircraft structure must be robust to the heat generated by the engine and to the loads exerted on them. Although a monolithic component formed of a high-performance material such as Inconel may be suitable, the density and cost of such materials is typically much higher than other aircraft materials such as Aluminium or Titanium and therefore it is desirable to minimise the use of materials like Inconel where possible. Such materials may be joined together with less dense or expensive materials by use of fasteners or similar, but this results in a component that comprises several parts increasing the bill of materials and introduces features that may need ongoing inspection such as drilled holes.

[0038] Accordingly, it is desirable to provide a multi-material monolithic component, which minimises the use of denser or more expensive materials without. requiring the added complexity of fasteners or similar. Such a multi-material component is particularly suitable for use in a pylon 4 for connecting an aircraft engine 2 to an aircraft wing 3.

[0039] With reference to Figure 3, a multi-material component 20 is shown according to an embodiment of this disclosure. The multi-material component 20 comprises a first member 22 formed of a first material and a second member 24 formed of a second material. The first material is preferably demonstrates better mechanical performance when hot than the second material. In particular, the first material may be a Nickel based superalloy such as Inconel, for example Inconel 718, Inconel 625, Alloy X-750 or any other similar material. The second material may be a typical aircraft material such as Titanium, for example Titanium 64, Titanium 6242, Titanium 6246, Titanium 1100, Titanium 17 or any other suitable Titanium alloy.

[0040] Nickel based superalloy describes a metallic alloy which is suitable for use at high temperatures, e.g maintains good mechanical properties at temperatures in and/or over temperatures of half the melting point, of the alloy, that contain a majority of Nickel with additions such as Aluminium or Titanium. Inconel is the main example of such a Nickel based superalloy but other alloys of Nickel also exhibit good mechanical properties at high temperatures.

[0041] The first and second member 22, 24 are joined together by a transition member 26. The joining may be achieved by way of additive manufacturing, such that the first, second and transition members 22, 24, 26 form a contiguous monolithic piece 20 without the need for fasteners. The transition member 26 comprises one or more materials arranged to form a secure bond with both the first member 22 and second member 24 as will be described later.

[0042] Since the multi-material component 20 is intended for use in coupling to or use near a heat source such as an aircraft engine, the multi-material component 20 may also feature means for reducing the heat conducted through the multi-material component 20, especially to reduce the heat encountered by the second member 24. With reference now to Figure 4 such heat mitigation means are described.

[0043] The multi-material component 30 comprises a first member 32, second member 34 and transition member 36 as before. The multi-material component 30 also comprises heat mitigation means for reducing the heat conducted through it from the first member 32 to the second member 34. In particular, there is provided a lattice 38 in the first member 32. The lattice 38 may be formed of the same first material as the first member, but comprises gaps or voids that. reduce its thermal conductivity when compared with the bulk first material. Alternatively the lattice may comprise a material compatible with the first material. Advantageously the material of which the lattice 38 is formed may have a lower thermal conductivity than the first material.

[00441 A second heat mitigation means of the multi-material component 30 is one or more channels 39 through the first member for receiving a cooling fluid. In use, a fluid such as air, water or any other appropriate coolant may be passed through the channels 39 in order to cool the first member 32 and reduce the amount of heat conducted through the first member 32 to the second member 34.

[0045] A multi-material component 30 according to this disclosure may comprise neither, one or both of the heat mitigation means being the lattice 38 and the one or more channels 39. Alternatively, the lattice 38 may provide channels 39 if the gaps or voids in the lattice 38 are contiguous, allowing them to act as a channel to receive a cooling fluid. This may be instead of or in addition to discrete channels 39 elsewhere in the first member 32.

[00461 When used in an aircraft 1, for example in a pylon 4, the first member 32 may be coupled to the engine 2 while the second member 34 may be coupled to the aircraft wing 3. Alternatively, the multi-material component 32 may be elsewhere in the pylon 4 away from the engine 2 but still exposed to the heat from the engine, in which case with the first member 32 being closer to the heat source than the second member 34. The multi-material component 30 thereby is available as a unitary body or monolithic component, simplifying assembly of the pylon 4. When compared lo multi-part structure 10, the parts count. and assembly requirements are reduced.

[00471 The first member 32 is formed of a material suitable for handling the high temperatures of the engine, while the thermal mitigation means (if present) help ensure that the second member 34 and the transition member 36 remain at a suitable temperature. It is at.

and immediately around the transition member 36 where there may be interfaces between the first and second material that could lead to the formation of brittle intermetallics. By shielding the transition member 36 from high temperatures the formation or propagation of such brittle intermetallics is reduced.

[0048] In particular, the lattice 38 serves to reduce the thermal conductivity of the first.

member 32. Accordingly the lattice 38 may serve to prevent any transient thermal loads significantly affecting the temperature of the second member 34 and transition member 36. Furthermore by reducing the rate of conduction to the second member 34 and transition member 36 any temperature change may be further mitigated by thermal transfer with the surrounding environment.

[0049] Furthermore, the cooling channels 39 may serve to reduce the amount of heat that may reach the second member 34 and transition member 36. In use on an aircraft 1, the air which the aircraft 1 is passing through may be an appropriate and readily available cooling fluid. Air can be drawn from outside the aircraft 1 and directed through the cooling channels 39 by ducts, fans or similar. Alternatively another coolant may be passed through the channels 39 which itself is cooled by means of a heat exchanger e.g. with outside air.

[0050] Since the first and second material arc different, they may have different coefficients of thermal expansion. Any stress induced in the multi-material component 30 is likely to be experienced most significantly along the join between dissimilar materials. In other words this strain is substantially parallel to the join between the first member 32 and transition member 36 or the second member 34 and the transition member 36.

[0051] With reference to Figure 5, an embodiment of multi-material component 40 is shown with employed with additional features to mitigate the impact of the mismatch in coefficients of thermal expansion. The multi-material component 40 comprises first member 42, second member 44 and transition member 46 as before (heat mitigation measures may or may not be present). Tt is further surrounded by lateral motion constraints 47. The constraints 47 reduce movement substantially parallel to the joints between the members 42, 44, 46 of the multi-material component. 40 Accordingly shear stress around the junctions between the transition member 46 and the first and second members 42, 44 is inhibited. This may improve the resilience of the multi-material component 40.

[0052] As shown here the lateral motion constraints 47 are single members either side of transition member 46 but. in other embodiments lateral motion constraints could consist of any number of members either side of multi-material component 40 and/or around the transition member 46.

[0053] The lateral motion constraints 47 may be provided by structural members of the aircraft 1, for example parts of the pylon 3. If the lateral motion constraints 47 are so provided then there is no need for additional parts, ensuring the parts count of the assembly remains low.

[0054] In a first embodiment, the transition member 26 may be created by depositing one or more layers of material via a process of additive manufacturing. Additive manufacturing may be any process by which material is gradually added to form a desired shape, and takes various forms suitable for use with various different material types, such as laser sintering of a powder or directed energy deposition of a metal bead.

[0055] A number of materials and additive manufacturing techniques have been identi fled that might be appropriate to form a transition member 26 capable of forming a strong connection to both the first material making the first member 22 and the second material making the second member 24. In particular, a pure or mostly pure layer of one of Tantalum or BAu-4 (Goldbraze 8218) have all been identified as candidate materials for such bonding. Furthermore, a double layer of Vanadium (for bonding to Titanium) and Copper (for bonding to Nickel-based superalloys like Inconel) has also been identified as a candidate.

[0056] Particularly suitable additive manufacturing techniques for depositing these materials are blown powder directed energy deposition (DED), laser metal deposition (LMD), extreme high speed laser application (LEILA), cold spray additive manufacturing (CSAM) and wire arc additive manufacturing (WAAM). However other additive manufacturing techniques may also be useable.

[0057] Tantalum is particularly suitable for forming the transition member 26. It has a high melting point, and experimental results suggest even a thin layer of around 1-3mm effectively inhibits diffusion between a Titanium and Inconel sample, avoiding or reducing the formation of brittle intermetallics. The phase diagrams of Tantalum with Titanium and Nickel show good compatibility with both materials, supporting results showing good bonding.

[0058] A further advantage of Tantalum for forming the transition member 26 is its relatively high ductility, which allows a transition member 26 formed of Tantalum to deform somewhat., improving the resilience of the eventual multi-material component. 20. This is particularly helpful since the differing coefficients of thermal expansion of the first material and the second material may lead to deformation around the transition member 26.

[0059] A transition member 26 of Tantalum might be made using any additive manufacturing technique since it is simply a layer of a single material. The high melting point of Tantalum may necessitate higher delivered energy but WAAM with a wire having a diameter of roughly lmm, for example in the region of 0.8-1.6mm. or more generally in the region of 0.5-2mm might be quite achievable. Since a thickness for such a transition member may be as low as about lmm this would provide an acceptable solution. For LMD and EHLA a Tantalum powder with a size on the order of tens to hundreds of microns might be most appropriate, for example less than 50 microns, less than 100 microns, or even less than 300 microns.

[0060] Instead of Tantalum, BAu-4 has similarly been identified as a material for forming the transition member 26 that is predicted to bond well to both Nickel and Inconel. Similar deposition techniques as used with Tantalum are likely to be successful [0061] Vanadium/Copper have also been identified as a promising combination of materials for forming a bilayer transition member. With reference now to Figure 6, a multi-material component 60 having such a bilayer transition member 66 is shown. It has a first member 62 and second member 64 as with other embodiments. The transition member 66 compfises a first transition layer 67 and a second Mmsition layer 68. The first transition layer 67 comprises Copper and is situated between the first. member 62 and the second transition layer 68. The second transition layer 68 comprises Vanadium and is situated between the sccond member 64 and the first transition layer 67.

[0062] Inspection of Vanadium/Titanium phase diagrams reveals that Vanadium forms good bonds with Titanium, without the formation of brittle interinetallics. The same can be said for Copper and Nickel. Vanadium and Copper are also compatible materials, that have unlimited mutual solubility and do not form brittle intermetallics. Accordingly, by arranging the first transition layer 67 and second transition layer 68 in this way, the only combinations of materials in contact. with each other are those which bond well together via metallic bonding.

[0063] Any of the additive manufacturing techniques identified for use with Tantalum and BAu4 are likely to be suitable for use with Vanadium/Copper. It is particularly advantageous to use a process that involves a relatively low heat input., to keep the dilution zone small such that there is no deep mixing of the materials. This is particularly important if the transition member 66 is being made in situ on the first member 62 or second member 64 since it helps to prevent the non-adjacent layers from mixing with each other, e.g. the Nickel based superalloy of the first member 62 with the Copper of the second transition layer 68. Such deep mixing would result in the meeting of incompatible materials and may lead to weaker bonding and the formation of brittle intermetallics. Ideally there should be no overlap between the dilution zones, which can be achieved by keeping energy levels low and/or travel speeds of a deposition head (where used) high.

[0064] One way to minimise the size of the dilution zone is to use CSAM as the additive manufacturing technique to create the bilayer transition member 66. Suitable powder sizes could be in the region of 40 to 120 microns or more generally 20 to 240 microns.

[0065] The first transition layer 67 and second transition layer 68 are preferably relatively thin. In the case of WAAM they may be made using only a single layer or material. An appropriate thickness might be in the region of lmm to 5mm, or more preferably around 1mm to 2mm.

The transition member 66 could be made as part of the multi-material component 60 in a multi-material additive manufacture process, starting with the first member 62, then the first transition layer 67, then the second transition layer 68, then the second member 64. Alternatively the order of operations could be reversed, starting with the second member 64, then second transition layer 68, then first transition layer 67, then first member 62. Further alternatively one or both of the first member 62 and second member 64 could be joined to the transition member 66 in a different way.

[0066] Although each of the materials above has been associated with at least one additive manufacturing techniques, it is reasonable to suspect that they might be usable with other additive manufacturing techniques, in particular from those identified above but also any other suitable additive manufacturing technology.

[0067] A transition member 26 so made according to the first embodiment may then go on to be used in the manufacture of the multi-material component 20. This may be via ongoing additive manufacture on opposite sides of the transition member 26 (or the transition member 26 may have been made upon one of the first or second member 22, 24). A similar additive manufacturing technology to that used to make the transition member 26 may be used to make the rest of the multi-material component 20. Alternatively a dissimilar method may be used that might provide more rapid manufacture. Further alternatively non-additive manufacturing techniques could be used, e.g. welding.

[0068] In a second embodiment, the transition member 26 comprises a stabilised mixture of the first material and second material. In particular, nanoparticles of Vanadium Carbide have been identified as a potential way to stabilise a mixture of the first material and the second material.

[0069] Vanadium Carbide is a ceramic which has the potential to bond well to Titanium and Inconel. It is identified here as a candidate for stabilising a mixture of Titanium and Nickel based superalloy, particularly Inconel, in nanoparticle form. It is predicted that nanoparticics of Vanadium Carbide in a Titanium/Inconel matrix will improve the tensile strength of the resulting structure. The Vanadium Carbide particles prevent or inhibit the formation of large regions of brittle intermetallics. Furthermore they prevent or inhibit the movement of dislocations within the Titanium/Inconel matrix, keeping the bond strong. Any nanoparticle of between I and 500nm may demonstrate improvements but in particular a range of between 20 and 200nm has been identified as a candidate.

[0070] Vanadium Carbide nanoparticles could be introduced into a mixture of Titanium and Inconel via a variety of additive manufacturing technologies. Any technique which melts or partially melts (softens) the upper layer of the substrate before the application of more material would be particularly suitable for incorporating Vanadium Carbide nanoparticles into the substrate before the different matrix material is then added on top. For example, LMD and DED would be a suitable additive manufacturing technique for doing so.

[0071] Once the Vanadium Carbide nanoparticles have been added to a substrate material, the addition of the next material above, with the inherent at least partial melting of the substrate layer, would lead to the two materials mixing to form a transition layer which makes up the transition member 26. Vanadium Carbide nanoparticles would be distributed uniformly across the interface between the two materials, stabilising it as previously described.

[0072] Such a method could be carried out with either the first material or the second material as a substrate, since in either case the result is a transition layer between the two materials with nanoparticles mixed throughout. Since Titanium and Inconel or other Nickel based superalloys have different melting points the amount of energy needed may vary depending on which material is acting a substrate. Advantageously, the energy delivered is sufficient to melt the top part of the substrate to allow for good incorporation of the nanoparticles.

100731 Such a transition member 26 could be deposited in situ upon either the first member 22 or second member 24, or alternatively be deposited as a separate component to be attached to the first member 22 and/or second member 24 by other conventional means.

100741 An alternative additive manufacturing technique for introducing the nanoparticles of Vanadium Carbide is the use of cored wire in WAAM or similar methods. A cored wire is a hollow wire made of a material, into which a powder can be added containing any number of materials. This is commonly used to experiment with different alloying mixtures in small batches. A cored wire of Titanium or a Nickel based superalloy could be filled with Vanadium Carbide nanoparticles (with or without other materials e.g. Titanium or Nickel) in order to introduce the nanoparticles into the material. This is particularly suitable since the cored wire technique helps overcome the surface tension of the melting pool to help the Vanadium Carbide nanoparticles to be dispersed within it.

100751 Ideally, the wire could include both Titanium and Nickel based superalloy (either as the wire or in the core) as well as Vanadium Carbide nanoparticles, which would permit the transition member 26 to be deposited in a single pass. Of course, instead of a cored wire a wire containing a mixture of Titanium and/or Nickel based superalloy with nanoparticles of Vanadium Carbide could be used.

[0076] A further alternative manufacturing technique suitable for making this kind of transition member 26 is powder metallurgy. By mixing together powders of Titanium, Nickel based superalloy, and Vanadium Carbide nanoparticles, the proportions of each in the transition member 26 can be controlled very precisely. Once appropriately mixed, the mixture can then be heated (possibly under pressure) in an oven, or via other heating techniques e.g. resistive or inductive heating. This fuses the powders together to create a transition member 26 that can then be built upon in the same way as others described herein.

[0077] In a third embodiment, the transition member 26 may be created by a process of welding together two dissimilar materials. With reference to Figure 7, such a transition member 50 is shown in more detail. The transition member 50 compiises a first transition layer 52 for joining to the first member and a second transition layer 54 for joining to the second member. The transition member 50 may further comprise a diffusion barrier 56 for preventing or reducing any d' f fusion o I material between the first and second transition layers 52, 54.

[0078] It has been found that suitable materials for the first transition layer include aged Inconel, for example aged Inconel 718. -Aged" denotes material that has been pre-aged via heat treatment. A typical heat treatment regime might be solutionizing between 950-990 degrees Celsius followed by a two stage aging of eight hours at 720 degrees Celsius then eight hours at 620 degrees Celsius. The skilled person will appreciate that many other aging regimes may be appropriate.

[0079] An alternative material for the first transition layer is pure Nickel. This may be Nickel of a commercially available purity, for example more than 99% pure, or more preferably more than 99.5% pure. 99.6% pure Nickel was found to provide acceptable performance.

[0080] It has been found that Titanium is a suitable material for the second transition layer. In particular, Titanium 64 has been found to provide appropriate performance. Alternatively pure Titanium may be used. This may be Titanium of a commercially available purity, for example more than 99% pure, or more preferably more than 99.5% pure. Advantageously purities of 99.6% or more may be used. Further alternatively other Titanium alloys may be suitable.

[0081] Preferably, the diffusion barrier 56 is included and comprises a thin film of material with a high melting point. Tantalum was found to be particularly effective, which has a melting point in the region of three thousand degrees Celsius. A layer of lmm was found to be sufficient, or alternatively a layer between 0.5 and 1 5mm or more generally a layer of between 0.2 and 5mm may be desirable. As an alternative to Tantalum. BAu4 may also be suitable for use as diffusion barrier 56.

[0082] Since the first transition layer 52 and second transition layer 54 are made of two usually incompatible materials, an unconventional welding approach is taken to reduce the intermixing of the two materials and to keep the join between the two strong. Particularly suitable welding technologies are explosion welding, linear friction welding and friction stir welding. Of these explosion welding has been found to produce a particularly strong join.

[0083] These welding techniques can result in a good bond between the welded members that involves minimal mixing between the two members, especially in the case of explosion welding, which is desirable to avoid the formation of brittle intermetallics. The diffusion barrier 56 helps to keep the materials of the first transition layer 52 and second transition layer 54 separate, during both the welding process and the long term use of the multi-material component 20, which is particularly important when the transition member 50 may be exposed to prolonged periods of relatively high temperature exposure.

[00841 A first transition blank and second transition blank are welded together to form the first transition layer 52 and second transition layer 54 respectively. The resulting transition member 50 may be subject to further machining, before being joined to the first member 22 (not shown) and second member 24 (not shown) in any appropriate way. The first. transition layer 52 is joined to the first member 22, and the second transition layer 54 is joined to the second member 24, since they respectively have compatible materials. This may be done via a further step of welding, or more preferably by building the first and second members 22, 24 upon the transition member 50 via additive manufacturing of any appropriate type.

[0085]The diffusion barrier 56 may be included as a diffusion barrier blank which is welded between the first transition blank and second transition blank. This could be as a separate component of the welding process, or more preferably included as a layer on one or both of the first transition blank and second transition blank prior to welding.

[0086] The transition member 50 formed via such approaches produces a join that compares well with the prior art bolting approach. A sample obtained via explosion welding was tested and the tensile strength of the join (across the join) was found to be in the region of 600 MPa. The shear strength (along the join) was found to be in the region of 400 MPa. Furthermore, the performance of the join was not significantly degraded after prolonged heat treatment (1000 hours at 400 degrees Celsius), indicating that in use the join will remain robust throughout a long lifetime, for example the lifecycle of an aircraft.

[0087] The multi-material component 20 may be created by joining the transition member 26 between the first member 22 and the second member 24. Since the transition member 26 of both the first, second and third embodiments is compatible with the material of the first member 22 and the second member 24 (when correctly aligned if necessary) this may be via a number of conventional methods since there is a reduced requirement to avoid diffusion between the first and second member 22, 24 on the one hand and the transition member 26 on the other hand.

[0088] One preferred option for both providing and joining one or more of the first member 22 and the second member 24 to the transition member is additive manufacturing, which permit the growth of the first member 22 and/or second member 24 upon the transition member 26. In the case of the first embodiment where the transition member 26 is obtained via additive manufacturing, the multi-material component 20 may be made via multi-material additive manufacturing without intermediate processing steps. The first. member 22 can be grown from the first material, then the transition member 26 grown upon the first member 22, then the second member 24 can be grown from the second material upon the transition member 26. Alternatively the order of operations may be reversed, with the second member 26 being grown first.

[0089] In the case of either thc first, second or third embodiment, the first member 22 and second member 24 could instead be grown sequentially upon the transition member 26 via single-material additive manufacturing, by depositing one of them first before re-orienting the growing multi-material component 20 to receive the second of them.

[0090] Before the joining of the first member 22 and/or second member 24 to the transition member 26, the transition member may be subject to additional processing. For example, it may be desirable to shape the transition member 26 to better conform to the planned use or to increase the strength of the transition member 26 in particular directions. Since in embodiments the transition member 26 is generally stronger in tensile strength than shear strength orienting it to increase the proportion of strain in use encountered as tension may be particularly desirable. Shaping the transition member 26 may take the form of bending it and/or machining it.

[0091] As the first member 22 is made from the first material, it may be desirable to incorporate one or both of the lattice 38 and channels 39 depicted in Figure 4. The lattice 38 may most simply be provided by a process of additive manufacturing, which makes forming the voids in the lattice straightforward. Alternatively the lattice could he constructed as a separate component and joined to the first member 22 or have the first member 22 grown around it. via additive manufacture. The channels 39 may be provided simply by drilling, or by leaving contiguous voids during the additive manufacture of the first member 22, which may form part of the lattice 38.

[0092] Once the multi-material component 20 has been created, it may be subject to further processing and machining to achieve the desired shape. For example, it may be machined in order to fit closely with the lateral motion constraints 47 shown in Figure 5 or otherwise to connect to other parts of the aircraft 1.

[0093] Although the terms "first member" 22 and "second member" 24 have been used to refer to two parts of the multi-material component 20 the skilled person will realise that these are labels, rather than directions indicating the order in which they should be made or assembled. The multi-material component 20 may be made using either of the second member 24 or the first member 22 being the first elements made.

[0094] Although the invention has been described above with reference to one or more preferred examples or embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims. Those features present in one embodiment may be suitable for use combined with other embodiments.

[0095] Although the invention has been described above mainly in the context of a metallic multi-material component for use in an engine pylon in a fixed-wing aircraft application, it may also be advantageously applied to various other applications. The multi-material component of this disclosure could be used in any part of an aircraft where a significant thermal load is encountered. For example the embodiments of this disclosure could be used elsewhere in the aircraft near to the engine without being directly connected to it, for example elsewhere in the engine pylon, the engine nacelle, or adjacent to the engine. Other heat sources might include the auxiliary power unit of an aircraft, fuel cells or similar. Furthermore the invention could be used in other settings, including but not limited to applications on vehicles such as helicopters, drones trains, automobiles and spacecraft.

[0096] Where the term -or" has been used in the preceding description, this term should be understood to mean "and/or", except where explicitly stated otherwise.

Claims

CLAIMS: 1. A method of creating a multi-material component, the method comprising: a step of making a transition member comprising a first transition layer and a second transition layer, the making being carried out by: providing a first transition blank formed of a material selected from the group consisting of aged Inconel 718 and pure Nickel; providing a second transition blank formed of Titanium; and welding the first transition blank and the second transition blank together via a method selected from the group consisting of explosion welding, linear friction welding and rotary friction welding, the first. transition blank and second transition blanks respectively forming the first transition layer and the second transition layer; a step of making a first member of a Nickel based superalloy; a step of making a second member of Titanium; and a step of joining the transition member between the first member and second member, the first transition layer being joined to the first. member and the second transition layer being joined to the second member, such that the transition member securely joins together the first member and the second member.
2. A method according to claim 1, further comprising a step of shaping the transition member before the step of joining the transition member between the first member and the second member.
3. A method according to any preceding claim, further comprising a step of providing a diffusion barrier blank and wherein the step of welding the first transition blank and second transition blank together comprises welding the diffusion barrier blank in between the first transition blank and second transition blank.
4. A method according to claim 3, wherein the diffusion barrier blank is provided on the surface of one of the first transition blank and second transition blank.
5. A method according to claim 3 or 4, wherein the diffusion barrier blank comprises Tantalum.
6. A method according to any preceding claim, wherein the step of joining the transition member between the first member and second member comprises making by additive manufacturing at least. one of the first. member and second member on the transition member.
7. A method according to any preceding claim, wherein the step of making the first member of a Nickel based superalloy comprises a step of making a lattice in the first member, the lattice having a lower thermal conductivity than the rest of the first member for reducing the rate of thermal transfcr through the first member to the sccond member.
8. A method according to any preceding claim, further comprising a step of making channels through the first member for receiving cooling fluid to cool the first member.
9. A method according to any preceding claim, wherein the steps of making the first and second member and the step of joining is carried out via a process of additive manufacture upon the transition member.
10. A method according to any preceding claim, comprising a further step of machining the multi-material component to obtain a desired shape.
11. A method according to any preceding claim, further comprising a step olproviding lateral motion constraints around the transition member for mitigating shear stress in the multi-material component.
12. A multi-material component comprising: a first member formed of a first material; a second member formed of a second material, and a transition member; situated and joined between the first member and the second member; wherein the first material is a Nickel based superalloy; die second material is Titanium; and the transition member comprises a first transition layer joined to the first member and a second transition layer joined to the second member; the first transition layer comprising a material selected from the group comprising aged Inconel 718 and pure Nickel, the second transition layer comprising Titanium.
13. A multi-material component according to claim 12, wherein the transition member further comprises a diffusion barrier between the first transition layer and the second transition layer.
14. A multi-material component according to claim 13 wherein the diffusion barrier comprises a layer of Tantalum.
15. A multi-material component according to claim 12, 13 or 14 wherein the second transition layer comprises a material selected from the group consisting of Titanium 64 and pure Titanium.
16. A multi-material component according to any one of claims 12 to 15, further comprising a lattice in the first member for reducing the rate of thermal transfer through the first member to the second member.
17. A multi-material component according to any one of claims 12 to 16, further comprising channels through the first member for receiving cooling fluid to cool the first member.
18. An aircraft comprising the multi-material component of any one of claims 12 to 17.
19. An aircraft according to claim 18, where in the aircraft comprises lateral motion constraints around the transition member for mitigating shear stress in the multi-material component.
20. A transition member for joining to a first member formed of Nickel based superalloy and a second member formed of Titanium, the transition member having been obtained by a process of welding and being comprising a first transition layer for joining to the first. member comprising a material selected from the group comprising aged Inconel 718 and pure Nickel and a second transition layer for joining to the second member comprising a material selected form the group comprising Titanium 64 and pure Titanium