This invention relates generally to a method of manufacturing a component for use in high temperature environments, e.g. jet engines, using bonding materials. More specifically, although not exclusively, this invention relates to a method of manufacturing a component having an internal structure using bonding materials. One such use for an internal structure might be to provide or facilitate cooling, e.g. to form or facilitate an effusion or transpiration internal cooling system.

Components for use in high temperature environments such as jet engines, e.g. high pressure turbine blades, nozzle guide vanes, and seal segments, often require internal cooling systems to prevent overheating and melting in service. Such components may be manufactured from superalloys; for the highest temperature applications single crystal cast nickel superalloys are required. The design of these internal cooling systems is becoming ever-more complex to realise improved operating efficiencies through increases to the temperature of the hot gas stream in which they operate. These internal cooling systems comprise complex networks of passageways, which allow cooling fluids such as air to flow through the component, past and through defined channels and features, which absorb and expel the heat diffusing inwardly from the external hot gas stream arising from the combustor. The features of the design of these internal cooling systems may be varied to increase complexity and improve the effectiveness and magnitude of heat transfer from the component to the cooling air. For example, the feature dimension, feature spacing, wetted surface area, and flow path length between the inlets to and outlets therefrom may be varied to improve cooling effects. This facilitates operation of components in jet engines at temperatures above the melting points of the alloys from which they are manufactured.

Components having internal cooling systems may be manufactured by investment casting. In this process, a metal is cast around an expendable ceramic pattern, which is then removed either mechanically or chemically subsequent to solidification.

Advancements in jet engine technology have led to higher operating temperatures. In turn, this means that there is an increasing need for components to have internal cooling systems with ever increasing cooling capabilities, and such changes to cooling requirements typically require increasingly complex internal structures. However, it is becoming increasingly difficult to make further advances using investment casting to manufacture these components because there is a limit to the complexity of the passageways in the networks that can be defined using investment casting methods alone.

It is known to manufacture increasingly complex internal cooling designs on single crystal components through the use of two or more separate machined parts which are subsequently joined to one another to form the component.

US2019323359A1 describes the manufacture of a turbine blade. The method comprises the steps of forming a plurality of columns on an outer surface of a first structure, forming a plurality of columns on a surface of each of a plurality of parts of a second structure, and forming a double walled section of an aerofoil by attaching the ends of columns on each part of the second structure to the ends of the columns on the first structure such that the first structure is an inner wall of the section of the aerofoil and the second structure is an outer wall of the section of the aerofoil. The plurality of columns are formed through a plurality of machining operations. The ends of the pedestals are flat and are joined together by diffusion bonding. The resulting internal cooling system design comprises impingement holes and effusion holes, the design of which may be varied to increase cooling capabilities.

As will be appreciated, it is essential to hold the two parts in accurate registry to ensure there is no mis-alignment.

US6638639B1 describes the manufacture of turbine components comprising thin skins bonded to superalloy substrates. The turbine blade airfoil comprises a substrate provided as two or more separate castings, which is bonded along a blade camber-line to form the airfoil. The airfoil also comprises a thin skin, which is bonded to the substrate using a transient liquid phase bonding process. A bonding foil may be applied as a single sheet of foil across the solid surface of the skin to ensure that the bond foil is applied to all of the possible regions that may be subjected to bonding. Or the foil may be formed so that it only contacts the areas which are required to bond.

However, these processes have a number of drawbacks. For example, templating the bonding foil to match the surfaces to be joined is time consuming and presents difficulties in alignment. In addition, it has been found that the use of excess or misaligned bonding foil in the process may lead to the alloy spreading between the intricate contacting features to be bonded. The flow of cooling air through the passageways of the cooling system may then be compromised due to impingement of the excess bonding material. This is deleterious to performance and may result in a high volume of scrap. The problems become more significant with increasing complexity of the passageways and features in internal cooling system designs.

Therefore, there is a need to provide a more efficient method of combining parts to form components for use in high temperature environments.

It is therefore a non-exclusive object of the invention to provide a method of manufacturing a component, e.g. for use in a high temperature environment such as a jet engine, which mitigates or solves one or more of the above-described problems.

Accordingly, a first aspect of the invention provides a method of manufacturing a component for use in a high temperature environment, e.g. from 950 to 2100 °C, the method comprising the sequential steps of: i) providing a first substrate comprising a body having a surface, ii) securing a bonding material to the surface of the first substrate, iii) removing at least some of the substrate and bonding material to provide a formation extending into the body, and iv) securing a second substrate to the first substate using at least some of the bonding material to form a component.

Advantageously, by securing the bonding material to the surface of the first substrate before the formation is formed, the excess bonding material is removed, which avoids or at least limits he possibility of ingress or spreading of excess bonding material into the passageway created by the formation. This reduces the amount of scrap because fewer components are unfit for purpose and/or reduces the risk of undetected occurrence of spreading and failure in service which might compromise performance.

In embodiments, the method may further comprise an initial step of cleaning the surface of the first substrate before the bonding material is located thereon. Cleaning ensures that the surface is free of dust, dirt, grease and other detritus. In embodiments, this may comprise cleaning the surface with a liquid, for example an organic solvent. A suitable liquid is acetone. Additionally or alternatively, the first substrate may be exposed to ultrasonic waves. The method may comprise an initial step of cleaning the surface of the bonding material before it is located on the first substrate. Cleaning ensures that the bonding material is free of dust, dirt, grease and other detritus. In embodiments, this may comprise cleaning the bonding material with a liquid, for example an organic solvent. A suitable liquid is acetone. Additionally or alternatively, the bonding material may be exposed to ultrasonic waves.

In embodiments, the method may further comprise the step of cleaning the surface of the second substrate before it is secured to the first substrate. This may comprise cleaning the surface with a liquid, for example an organic solvent. A suitable liquid is acetone.

In embodiments, the method may further comprise preparing the surface of the first substrate and/or the surface of the second substrate to optimise the surface roughness. In embodiments, this may comprise using an abrasive material. In tests we have found that the use of sandpaper, e.g. 120 grade paper is useful or grinding paper, e.g. 320 grit silicon carbide paper. Additionally or alternatively, the surface may be shot blasted, sand blasted, grit blasted or soda blasted, or linished or laser treated.

In terms of surface finish, it has been found that, at one extreme, a highly polished surface and, at the other extreme, a heavily etched surface (such as is provided by an as-cast part), do not provide optimal results in terms of bond formation between the first substrate and bonding material and the second substrate and the bonding material.

The first substrate and/or the second substrate may be formed from a single crystal. In embodiments, the first substrate and/or the second substrate is formed from a superalloy, for example a cast nickel superalloy, e.g. CMSX-2, CMSX-3, CMSX-4, CMSX-8, CMSX- 10K, CMSX-486, CMSX-681 , and family members, e.g. CMSX-4 Plus (SLS) or CMSX-10K or N (the chemical composition of all of which can be seen in “Improved 3 ^rd Generation Single Crystal Superalloy CMSX-4 Plus (SLS) - a study of evolutionary alloy development’ Wahl and Harris - available from www.cannonmuskegon.com). In embodiments, the first substrate and/or the second substrate may each be formed from a cast nickel superalloy single crystal. The first substrate may have the same or different composition as that of the second substrate In embodiments, step iii) may comprise removing substrate and bonding material to provide plural formations.

In embodiments, step iii) may comprise removing at least some of the substrate and bonding material to provide a series, pattern or array of formations extending into the body. Advantageously, the series pattern or array of formations may be extremely complex.

Once the second substrate is secured to the first substrate, the one or more formations formed in the first substrate may provide one or more channels in the joined part. The channel or channels may provide one or more conduits for fluid flow, for example to provide one or more cooling channels.

In embodiments, the formation or series of formations may define one or more walls, pillars, pedestals, spars, ribs, fins, baffles and/or castellations. The formations may be provided to afford the component cooling passages and/or to provide appropriate sites on the first substrate to facilitate bonding to the second substrate.

In embodiments, step iii) may be performed using a machining technique appropriate for the material, e.g. low stress mechanical machining, electrical discharge machining (EDM), die sinking EDM, cavity EDM, volume EDM, laser ablation and so on.

In embodiments, the first substrate and/or the second substrate may comprise one or more apertures extending through the body. The one or more apertures may, in use, provide effusion holes for the egress or ingress of fluids, for example cooling fluids. The one or more apertures may be fluidly connected to the one or more formations. In embodiments, the aperture or apertures, e.g. effusion hole or holes, may be formed using a machining technique, e.g. electrical discharge machining (EDM) or formed in-site within the substrate during casting.

As will be appreciated, by securing the bonding material to the first substrate before the one or more formations are created the bonding material does not need to be accurately aligned on the first substrate. Further, there is no need to template the bonding material when providing one or more formations, and especially when a complex series of formations is required. Because excess material is removed there is much less of a risk of excess bonding material ingressing into the series of formations when the first substrate is secured to the second substrate. Also, because there is no need to accurately register the bonding material to the first substrate there is less of a risk of waste of expensive substrate material caused by mis-alignment.

The bonding material is preferably a nickel-based alloy. In embodiments, the bonding material is a nickel-based alloy comprising one or more of boron or silicon. In embodiments, the nickel-based alloy is or comprises one or more of a Ni-Si-B and/or Ni-Cr-B based alloy. It has been surprisingly found that Ni-Cr-B based alloy has better wetting characteristics. In embodiments, the bonding material has the following composition: Ni (bal.), 15% Cr, 3.5% B (all wt.%). Other suitable bonding foils which may be used are disclosed in Table 1 of US6638639.

The bonding material preferably has a melting temperature lower than that of the material of the first substrate and/or the melting point of the material of the second substrate.

In embodiments, the bonding material is or comprises a bonding foil. In embodiments, the bonding material is or comprises a paste or may be deposited by, for example, electrophoretic deposition.

In embodiments, the bonding material is applied to a thickness of from 20 to 50 microns (10 ^-6 m). Preferably, the bonding material is a foil having a thickness of between 20 to 50 microns, e.g. 25 to 45 microns, or 30 to 40 microns, e.g. 38 microns.

In embodiments, the bonding material is a melt spun bonding foil. Manufacture using melt spinning causes a thin layer of molten alloy to rapidly solidify to produce an amorphous metallic sheet.

The use of foils is advantageous because they can be produced to tight tolerances. In particular, the use of melt spun bonding foils provides foils with exacting thickness tolerances. Further, the process of application to the first substrate is simple and relatively quick to perform.

In embodiments, step ii) may comprise a first step iia) of securing the bonding material in place on the surface of the first substrate. If the bonding material is a foil the first step iia) may be performed using spot welding. Additionally or alternatively, at least a part of the periphery (or other portion) of the bonding material may be retained in place or held within slots, apertures or formations in the first substrate. It is also possible to hold the foil in place, for example mechanically hold the foil in place, for example using clamps, bolts etc.

In embodiments, step ii) may comprise securing the bonding material to the surface of the first substrate using heat. For example, the first substrate and bonding material may be subjected to a high temperature environment. The high temperature environment is preferably a non-oxidising high temperature environment and is most preferably a nonoxidising high temperature environment which is nitrogen free. One such high temperature environment is a vacuum high temperature environment. Alternative, the high temperature environment may comprise an atmosphere of an inert gas (argon, neon, helium etc).

The use of heat in step ii) may comprise a second step iib) which occurs after the first step iia).

The bonding material may be secured to the surface of the first substrate using the initial period of a transient liquid phase diffusion bonding process.

For the avoidance of doubt, transient liquid phase diffusion bonding is a joining process that produces high quality joints in superalloys. In this case, the bonding material is located on the surface of the first substrate. The resulting article is heated to a temperature above the melting point of the bonding material, but below the bulk melting point of the first substrate. The bonding material preferably has a similar composition to that of the first substrate, but also includes a melting point depressing component that also exhibits rapid solid state diffusion in the substrate alloy. In embodiments in which the bonding material is a nickel based alloy, melting point depressants may be included in the bonding material. Many elements are envisaged as melting point depressants, such as boron and/or silicon and/or beryllium. As the bonding material melts, it wets the first substrate, and causes some dissolution of the material from which the first substrate is manufactured. This provides a wider liquid zone, which causes boron to be depleted from the liquid state bonding material. Solid state diffusion of boron also causes the melting point depressant (e.g. boron) to be removed from the bonding material, whilst diffusion of alloying elements contained within the substrate diffuse in to the joint layer. The concurrent and progressive diffusion of the melting point depressant (e.g. boron) and homogenisation of the composition toward that of the substrate thereby increases the melting point of the layer, causing it to solidify isothermally. These three processes lead to isothermal resolidification of the bonding material at the interface between the first substrate and the bonding material, securing them together.

In embodiments, in step ii) the bonding material may be secured to the surface of the first substrate by heating to a temperature above the melting point of the bonding material, which we call the first securement temperature. In embodiments, the first securement temperature may be from each of 1 , 2, 3, 4 or 5 to each of 50, 40 or 30 °C, e.g. from 10 to 25 °C, above the melting temperature of the bonding material. In embodiments, step ii) comprises heating at or above the first securement temperature for a period of time less than 20 minutes, e.g. less than 19, 18, 17, 16, 15, 14, 13, 12, 11 , 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 minute. In embodiments the temperature period may be from 1 to 20 minutes, say from 5 to 20 minutes.

The first securement temperature for a nickel based bonding material (e.g. Ni-15Cr-3B) may be from 1000 to 1200°C, for example from 1050 to 1100°C.

In embodiments, step ii) may be performed within a desired temperature range and may be conducted isothermally.

In performing step ii) the substrate and the bonding material may be subjected to an environment in which the temperature increases from ambient to the first securement temperature using a defined temperature ramp rate. Once the substrate and bonding material have been subjected to a temperature at or above the first temperature securement temperature for a required time period the temperature may be reduced at a defined ramp rate (cooling rate) until it reaches ambient.

The ramp rate to raise the temperature may be between 1 and 50°C per minute, for example 10°C per minute. The ramp rate to raise the temperature may be constant.

The ramp rate to decrease the temperature may be between 1 and 400°C per minute. The material may be cooled by exposing it to a quenching gas, for example argon.

In an embodiment the ramp rate to decrease the temperature may be between 1 and 20°C per minute until the temperature reaches, say, 950°C. The cooling ramp rate may then be increased. In one embodiment the cooling rate may be increased by quenching the part with argon.

In embodiments, in step iv) the second substrate may be secured to the first substrate using heat. For example, the second substrate and first substrate (with bonding material attached thereto) may be subjected to a high temperature environment. The high temperature environment is preferably a non-oxidising high temperature environment and is most preferably a non-oxidising high temperature environment which is nitrogen free. One such high temperature environment is a vacuum furnace high temperature environment. Alternative, the high temperature environment may comprise an atmosphere of an inert gas (argon, neon, helium etc).

In step iv) the second substrate may be secured to the first substrate using a transient liquid phase diffusion bonding process.

The second substrate may have a surface and a body, the surface is to be attached to the first substrate using the bonding material. The surface may be featureless or formations may be provided in the body, for example extending into the body from the surface.

It should be noted that the boron concentration of the bonding material is highest before it is secured to the surface of the first substrate, it is depleted upon securing to the surface of the first substrate, and is further depleted upon securing the first substrate to the second substrate. Consequently, the melting point of the bonding material increases as melting point depressant (e.g. boron) is depleted and the substrate material dissolved in to it.

In step iv) the second substrate may be secured to the first substrate using at least some of the bonding material by heating to a temperature above the melting point of the bonding material, which we call the second securement temperature. In embodiments, the second securement temperature may be from 5 to 150 °C, e.g. from 10 to 100 °C, above the melting temperature of the bonding material. In embodiments, step iv) comprises heating at or above the second securement temperature for a period of time of up to 12 hours, say from 1 to 12 hours. It will be appreciated that the bonding temperature and times will be selected depending upon the nature and composition of the first substrate and/or the substrate, as well as the nature and composition of the bonding material.

In embodiments, step iv) may be performed isothermally or programmatically over a range of temperatures.

In embodiments, step iv) of securing a second substrate to the first substate using at least some of the bonding material may be performed under vacuum or in an inert gas, e.g. argon, atmosphere.

In step iv) the first and second substrates are held in registry, typically using a jig or clamping mechanism. It will be appreciated that the registration of the first and second substrate is necessary to ensure correct alignment of the formations within the component.

In embodiments, the method may further comprise cooling the bonded first and second substrate under vacuum.

In embodiments, the method may comprise performing a further heat treatment process on the component.

A further aspect of the invention provides a first substrate of a high temperature component for securement to a second substrate of said high temperature component, the first substrate comprising a body and a surface, the surface having a bonding material melt bonded thereto, the bonding material being for securement of the first substrate to the second substrate.

In embodiments, the first substrate of a high temperature component for securement to a second substrate of said high temperature component may have been manufactured in accordance with step ii) of the method outlined above. During this step, the first substrate preferably undergoes heating to secure the bonding material to the surface. Consequently, the bonding material melts upon and dissolves the near surface layer of the first material to provide an intimate and continuous interface. This contrasts to simply locating or fastening the bonding material to the surface, e.g. using spot welding. A yet further aspect of the invention provides a first substrate of a high temperature component for securement to a second substrate of said high temperature component, the first substrate comprising a body and a surface, and having at least one formation extending into the body from the surface, the surface having a bonding material melt bonded thereto, the bonding material being for securement of the first substrate to the second substrate.

In embodiments, a first substrate of a high temperature component for securement to a second substrate of said high temperature component may have been manufactured in accordance with step ii) and/or iii) of the method outlined above.

A further aspect of the invention comprises a component formed in accordance with the method and/or a component comprising a first substrate and second substrate joined together, wherein the first substrate comprises a body and a surface, the surface having a bonding material melt bonded thereto

Advantageously, the resulting bond between the first substrate and the second substrate is a homogenised joint possessing mechanical properties equivalent to or acceptably close to those of the individual bonded substrates such that they are fit for function.

Any of the previous statements relating to the method regarding the first substrate, the second substrate, and the bonding material may relate to any of the other aspects of invention. For example, the first substrate and/or the second substrate may be formed from a superalloy, for example a cast nickel superalloy, e.g. CMSX-4 or any of those disclosed above. For example, the bonding material may be a nickel-based alloy typically comprising one or more melting point depressants, for example one or more of boron, silicon or beryllium.

In embodiments, the component is for use in a jet engine. In embodiments, the component is, or is part of, a turbine blade, e.g. a high pressure turbine blade. In embodiments, the component is, or is part of, a nozzle guide vane. In embodiments, the component is, or is part of, a seal segment.

Although the above description and below examples exemplify the invention in relation to nickel superalloys, it will be appreciated that the invention is applicable to other alloy systems which are being, or are proposed to be, used in high temperature environments such as silicides, other ordered alloys, high entropy alloys which are all candidate materials for future generations of turbine components, for example.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. For the avoidance of doubt, the terms “may”, “and/or”, “e.g.”, “for example” and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1a is an unassembled component according to step i. of the method of the invention; and

Figure 1b is an intermediate product produced during the method of the invention;

Figure 1c is an intermediate product produced after step ii. of the method of the invention;

Figure 1d is an intermediate product produced after step iii. of the method of the invention;

Figure 1e is a component produced after step iv. of the method of the invention;

Figure 2a is photograph of a first substrate comprising a bonding material secured thereto according to the invention;

Figure 2b is a photograph of a machined first substrate comprising a series of formations having a bonding material secured thereto according to the invention;

Figure 2c is a GOM(RTM) photogrammetry image of the series of formations on machined substrate of Figure 2b; Figure 3 is a graph showing the heating process for securing the bonding material to the surface of the first substrate;

Figure 4a is a photograph of a component produced in the method of the invention;

Figure 4b is a photograph of a component of the prior art;

Figure 5 is a graph showing the heating process for securing the first substrate to the second substrate;

Figure 6a is a photograph of a bond formed between a first substrate and a second substrate in a component of the invention;

Figure 6b is a photograph of a bond formed between a first substrate and a second substrate in a component of the invention;

Figure 6c is a photograph of a bond formed between a first substrate and a second substrate in a component of the invention;

Figure 6d is a photograph of a bond formed between a first substrate and a second substrate in a component of the invention;

Figure 7a shows effusion holes in the first substrate;

Figure 7b shows effusion holes within an array of formations in the first substrate;

Figure 8a is a photograph of a first substrate comprising a bonding foil located thereon;

Figure 8b is a photograph of the first substrate of Figure 9a comprising the bonding foil secured thereto; and

Figure 8c is a diagram showing some of the angles in which testing was carried out to determine whether the orientation of the surface affected the bonding material thickness.

Referring now to Figure 1a to 1e there is shown a sequential illustrations demonstrating the steps used in the method.

Referring first to Figure 1a, there is shown a unassembled component 1 . The unassembled component 1 comprises a first substrate 10, a second substrate 11 , and a bonding material 12. The first substrate 10 comprises a body 10a having a surface 10b. The second substrate 11 comprises a body 11a and a surface 11b.

The first substrate 10 and the second substrate 11 have been machined or otherwise formed to create continuous matching surfaces. Clearly, in use, the first and second substrate will have shapes appropriate to the component to be formed (e.g. part shapes of a turbine blade or so on). This may be performed by locating the first and second substrate via datums. In this embodiment, the first substrate 10 and the second substrate 11 are each superalloy single crystal workpieces.

The surface 10b of the first substrate 10 and the surface 11b of the second substrate 11 have been prepared to optimise the surface roughness and cleaned to be free of dust, dirt, and grease.

The bonding material 12 is cleaned and is sized to fit the surface 10b of the first substrate 10.

Referring now to Figure 1b, there is shown an intermediate product 2. The intermediate product 2 comprises the bonding material 12 fastened to the surface 10b of the first substrate 10. In this embodiment, the bonding material 12 is spot welded in place on the surface 10b of the first substrate 10.

Referring now to Figure 1c, there is shown an intermediate product 3 according to an embodiment of the invention. The intermediate product 3 comprises the secured bonding material 13 bonded to the surface 10b of the first substrate 10. The secured bonding material 13 is melted-bonded to the surface 10b of the first substrate 10 in a vacuum heat treatment furnace using a thermal cycle just above, e.g. preferably 5 to 30 °C, or most preferably 10 to 25 °C above, the melting point of the bonding material 12 for a period of time that ensures the bonding material 12 melts but does not solidify isothermally.

It has been surprisingly found that securing bonding material 13 to the first substrate 10 using this process enables the layer to be molten for a limited period of time, such that the formed layer of bonding material 13 comprises sufficient elemental content for the bonding material 13 to subsequently bond the first substrate 10 to the second substrate 11. It has been found that restriction of the temperature in the vacuum heat treatment furnace to a temperature of 5 to 30 °C above the melting point of the bonding material 12, for a period of time of less than 10 minutes, secures the bonding material 13 to the first substrate 11 whilst retaining much of the boron within the bonding material 13, which depresses the melting point. This provides sufficient unreacted bonding material 13 for the total reaction to proceed when typical treatment temperatures and times are used to create the final union of the first substrate 11 to the second substrate 12. Advantageously, the bonding material thickness is not affected by the orientation of the surface 10b to be coated relative to the action of gravity. Therefore, a layer of secured bonding material 13 of sufficient uniformity can be realised upon even complex matching surfaces.

Referring now to Figure 1 d, there is shown a further intermediate product 4 according to an embodiment of the invention. The intermediate product 4 comprises the secured bonding material 13 bonded to the surface 10b of the first substrate 10. The first substrate 10b has been machined to remove at least some of the first substrate 10 and bonding material 13 to provide a series of formations 14a, 14b, 14c.... 14z extending into the body 10a of the first substrate 10.

The series of formations 14a, 14b, 14c.... 14z provide rebates to form an internal cooling system. As shown, the formations 14a... 14z define a plurality of pillars 15a... 15z, each of which is topped with a portion of bonding material 13’. It will be appreciated that the bonding material 13 is present only on the surface 10b of the first substrate 10 to be bonded to the surface 11 b of the second substrate 11.

Referring now to Figure 1e, there is shown a component 5 produced from the method of the invention. The component 5 comprises the first substrate 10 secured to the second substrate 11 using the bonding material 13, and specifically the intervening bonding material 13’ located atop each pillar 15a... 15z.

The first substrate 10 is secured to the second substrate 11 using a heat treatment furnace. The aligned first substrate 10 and second substrate 11 are loaded into the heat treatment furnace (not shown) for heat treatment under vacuum. The thermal profile is designed to ensure formation of a liquid layer of bonding material 13 therebetween that subsequently solidifies isothermally to bond the first substrate 10 to the second substrate 11 to form the component 5. The component 5 may also be cooled under vacuum.

Advantageously, any excess bonding material 12 is removed from the surface 10b of the first substrate 10 when the series of formations 14a, 14b, 14c, ...14z is created during the machining step, for example using EDM. This means that problems resulting from excess bonding material flowing into channels created by the formations is negated. In addition, the bonding material 12 is located in the correct position for securing the first substrate 10 to the second substrate 11 . There is no need to align the bonding material 12 to the surface 10a of the first substrate 10a, and the bonding material 12 is present in the correct places in the correct alignment.

The invention will now be exemplified as follows.

Referring now to Figure 2a, there is shown a photograph of the first substrate 10’ comprising a bonding material 13’ secured to its surface. The spot weld pools, e.g. 20, are shown. The first substrate 10’ was manufactured from CMSX-4 nickel based superalloy melting stock ingot. The bonding material was an amorphous foil having a nominal composition of Ni, 15% Cr, 3.5% B. The foil had a thickness of 38 microns. The conditions used to secure the bonding material 13’ to the surface of the first substrate 10’ were 1080 °C for 5 minutes. This is 25 °C above the melting point of the bonding material.

Referring also to Figure 2b, there is shown a photograph of the first substrate 10’ of Figure 2a having undergone machining using EDM to provide a series of formations, e.g. 14’.

Referring also to Figure 2c, there is shown a GOM(RTM) photogrammetry image of the series of formations on machined substrate 10’ of Figure 2b. The bonding material 13’ is clearly shown to be secured to the tops of the formations 14’ only.

Referring now to Figure 3, there is shown a graph showing the heating process for securing the bonding material to the first substrate according to the method of the invention. The heating process was used to secure the bonding material 12’ to the first substrate 10’ to form bonding material 13’ shown in Figure 2a. The heating process comprises the following steps:

• Heating at 10 °C per minute minimum until a temperature of 950 °C is reached;

• Isotherm at 950 °C for 15 minutes;

• Heating at 10 °C per minute minimum until a temperature of 1080 °C is reached;

• Isotherm at 1080 °C for 5 minutes;

• Cooling at 10 °C per minute minimum to 950 °C;

• Argon quench to cool to room temperature. Referring now to Figure 4a, there is shown a component 5’ comprising an internal cooling system according to the invention. The component 5’ comprises the first substrate 10’ having a series of formations 14’ and the second substrate 1 T. The component 5’ is shown wherein the first substrate 10’ has been secured to the second substrate 1 T in a bonding process using the bonding material (not shown). The conditions used were 1130 °C for 20 minutes followed by 1080 °C for 8 hours.

It is shown that there is no excess bonding material around the series of formations 14’ or within the passageways of the internal cooling system.

Referring also to Figure 4b, there is shown a component 50’ comprising an internal cooling system according to the prior art. The component 50’ comprises the first substrate 100’ having a series of formations 140’ and the second substrate 110’. The component 50’ is shown wherein the first substrate 100’ has been secured to the second substrate 110’ in a bonding process using the bonding material (not shown). It is shown that there is excess bonding material around the series of formations 140’ and within the passageways of the internal cooling system. This leads to inefficiency of the internal cooling system of the component because the passageway is partially blocked to cooling air.

Referring now to Figure 5, there is shown a graph showing the heating process for securing the first substrate to the second substrate according to the method of the invention. The heating process was used to secure the first substrate 10’; 100, to the second substrate 1 T, 110 for Figures 4a. The heating process comprises the following steps:

• Heating at 10 °C per minute minimum until a temperature of 950 °C is reached;

• Isotherm at 950 °C for 15 minutes;

• Heating at 10 °C per minute minimum until a temperature of 1130 °C is reached;

• Isotherm at 1130 °C for 20 minutes;

• Cooling at 10 °C per minute minimum to 1080 °C;

• Isotherm at 1080 °C for 8 hours;

• Cooling at 10 °C per minute minimum to 950 °C;

• Argon quench to cool to room temperature.

Referring now to Figures 6a to 6d, there is shown a series of photographs of bonds between a first substrate 10’ formed in accordance with the protocol; explained in Figure 2a or 2c, and a second substrate using the bonding material. Figure 6a shows the bond between the first substrate 10’ and the second substrate 1 T using the bonding material in a transient liquid phase bonding process under conditions of 1130 °C for 20 minutes.

Figure 6b shows the bond between the first substrate 10’ and the second substrate 1 T using the bonding material in a transient liquid phase bonding process under conditions of 1130 °C for 20 minutes followed by 1080 °C for 3 hours.

Figure 6c shows the bond between the first substrate 10’ and the second substrate 1 T using the bonding material in a transient liquid phase bonding process under conditions of 1130 °C for 20 minutes.

Figure 6d shows the bond between the first substrate 10’ and the second substrate 1 T using the bonding material in a transient liquid phase bonding process under conditions of 1130 °C for 20 minutes followed by 1080 °C for 8 hours.

The difference in the bonds formed during heat treatment of different durations is illustrated between Figures 6a and 6b, and between Figures 6c and 6d. It is shown that the bond between the first substrate 10’ and the second substrate 1 T is much wider, and the bonding material has dissolved the substrate material to a greater extent, in Figure 6d in comparison to Figure 6b.

Referring now to Figure 7a, there is shown a machined first substrate 10” having effusion holes, e.g. 51 , located through the body. Referring also to Figure 7b, there is shown the first substrate 10” wherein the impingement holes, e.g. 61 , are located throughout an array of formations, e.g. 14”. The effusion holes form part of the internal cooling system of the component, in use.

A series of experiments were set up to determine whether the angle at which the bonding material was applied and subsequently secured to the surface of the first substrate (via a transient liquid phase bonding process) affected the thickness of the secured bonding material Referring now to Figure 8a, there is shown a photograph of a model first substrate 1000 comprising a bonding material 1200 located thereon. The bonding material 1200 in this example is a foil having a thickness of 38 microns.

Referring also to Figure 8b, there is shown a photograph of the model first substrate 1000 comprising a bonding material 1300 which is secured to the surface of the first substrate 1000.

Referring also to Figure 8c, there is shown a diagram showing some of the different angles upon which the surface of the first substrate 1000 had the bonding foil 1200 secured thereto.

The table below shows the different angles at which the bonding material 1200 was applied to the surface of the model first substrate 1000, and the average thickness of the subsequently secured bonding material after a transient liquid phase bonding process. The data below is an average of a minimum of twelve measurement.

It is shown that the bonding material thickness is not affected by the orientation of the surface to be coated relative to the action of gravity. Therefore, a layer of secured bonding material of sufficient uniformity can be realised upon even complex matching surfaces.

It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention. For example,

It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.