Method of joining ceramic components

Abstract

There is provided a method of joining ceramic components comprising providing an interlayer between a first ceramic component and a second ceramic component, and heating the interlayer by passing an electric current through the interlayer to melt the interlayer and induce liquid phase diffusion bonding between the first ceramic component and the second ceramic component. Also provided is an article comprising joined ceramic components and an apparatus for joining ceramic components.

Description

Method of joining ceramic componentsField of the Invention

[0001] The present invention relates to a method of joining ceramic components, an article comprising joined ceramic components and an apparatus for joining ceramic components. Background

[0002] Ceramic articles, such as silicon carbide (SiC) or silicon carbide fibre composites (SiC / SiC) can be used as a structural material in fusion reactors, due to their desirable properties of high thermal, mechanical and chemical stability, whilst also providing high strength-to-weight ratio.

[0003] To be used as a structural material in a fusion reactor, large scale ceramic articles will be required, in the metre-scale. This means that ceramic components will need to be fabricated off-site, transported to their final location, and joined to form the ceramic article as a single unit.

[0004] It is therefore desirable to provide a method of joining ceramic components in which a hermetic joint between the components is as strong, thermally stable and irradiation-resistant as the surrounding components.

[0005] Existing methods of joining SiC to SiC typically use an intermediary as a bonding agent, namely brazing alloys, glassy-ceramics, and transient eutectic phases. However, the joints formed by these methods may not provide adequate performance at the temperatures and irradiation doses present in a fusion reactor. Another existing method of joining SiC to SiC is diffusion bonding, which requires very high pressures and temperatures and highly-polished surfaces, which are not suitable for the scale of joining required for articles for a fusion reactor. Furthermore, the sluggish heating rates involved in conventional diffusion bonding has the potential to damage the SiC fibres that make up SiC / SiC by exposing them to high temperatures (>1600°C) for long periods of time. It is therefore desirable to provide a method of joining SiC or SiC / SiC components that will form articles suitable for use in nuclear environments.Summary

[0006] According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

[0007] According to an aspect, there is provided a method of joining ceramic components comprising: providing an interlayer between a first ceramic component and a second ceramic component, and heating the interlayer by passing an electric current through the interlayer to melt the interlayer and induce liquid-phase diffusion bonding between the first ceramic component and the second ceramic component.

[0008] The method provides a process for joining ceramic components that does not require the high temperatures and pressures of existing diffusion bonding processes (typically temperatures of 1500°C-2000°C and pressures of up to 60 MPa). Instead, passing an electric current through the interlayer induces Joule (resistive) heating to high temperatures, which causes the interlayer to melt very quickly. The step of melting the interlayer may be achieved by passing a steady-state current through the material to be bonded or interlayer itself at increasing temperatures until the electrical resistivity of the material drops, causing rapid heating (thermal runaway) and what is known as a “flash”.

[0009] The molten interlayer provides a liquid phase for diffusion of portions of the ceramic component adjacent the interlayer to occur, causing atoms of the ceramic components to rearrange and bond with each other, providing a pure, near-seamless joint. The Joule heating provides local heating to high temperatures, which allows the joint to form through liquid-phase diffusion bonding whilst preventing regions of the ceramic components away from the interlayer to be heated to high temperatures. The joint can be formed in seconds or minutes, whereas typically diffusion bonding processes take tens of hours, which exposes the ceramic components to high temperatures for long periods of time. On melting the interlayer, the material of the interlayer may dissipate through the surrounding ceramic components, thereby leaving a joint that is nearly pure ceramic. Furthermore, the use of an interlayer may allow the joint to be formed on lower quality surfaces thereby providing a lower cost process, compared to existing diffusion bonding methods that require highly polished surfaces, for example 1 micron polished finish.

[0010] In examples, the first and second ceramic components may comprise a ceramic matrix composite (CMC). In examples, the first and second ceramic components may comprise silicon carbide or carbon fibre-reinforced silicon carbide composites. In examples, the ceramic components may comprise ultra-high temperature ceramic matrix composites, for example ZrB2, ZrC, HfC, HfB2.

[0011] The first and second ceramic components may comprise silicon carbide. The first and second ceramic components may comprise a silicon carbide fibre composite.

[0012] In examples, the first and second ceramic components may be liquid phase sintered ceramics. For example, the first and second ceramic components may comprise zirconium carbide and / or zirconium diboride.

[0013] The interlayer may be a foil. Providing the interlayer may comprise providing a foil between the first ceramic component and the second ceramic component. Use of a foil interlayer provides benefits in its simplicity as it may be added directly between the first ceramic component and the second ceramic component, as opposed to having to coat at least one side of one component in a separate process. Malleable foils may offer additional benefits, particularly on rough surfaces where they can deform to improve contact between surfaces, thus increasing bonding strength between the first ceramic component and the second ceramic component. By providing the interlayer as a foil, the interlayer may be applied readily and simply in the bonding method.

[0014] In examples, the interlayer may be a coating. Providing the interlayer may comprise applying the coating to at least one of the first ceramic component and the second ceramic component. The coating may be applied by plasma vapour deposition, preferably sputter coating.

[0015] The interlayer may have a thickness of less than or equal to 25 microns. The interlayer may have a thickness greater than or equal to 100 nanometres. In examples where the interlayer is a foil, the interlayer may have a thickness of several microns. In examples where the interlayer is a coating, the interlayer may be thinner than examples where the interlayer is a foil. Providing an interlayer less than 25 microns in thickness may allow sufficient dispersion of the material of the interlayer through the ceramic components to provide a near-seamless, pure joint. In examples, the interlayer may have a thickness of less than 20 microns, less than 15 microns, less than 10 microns or less than 5 microns. In examples, the interlayer may have a thickness of less or equal to 1 micron, but greater than 100 nanometres. In examples, the interlayer may have a thickness of greater than 300nm, or greater than 500 nanometres. In examples, the interlayer may have a thickness of greater than or equal to 1 micron, but less than or equal to 25 microns.

[0016] The interlayer may be a metal or metal oxide. The interlayer may be a rare earth metal or rare earth metal oxide.

[0017] The interlayer may comprise at least one of yttrium, yttrium oxide, aluminium, aluminium oxide, chromium and chromium oxide.

[0018] The method may comprise applying pressure to the components while heating the interlayer. The applied pressure may be less than or equal to 10 MPa. This applied pressure may be less than the pressure typically applied in existing diffusion bonding processes of up to 60 MPa.

[0019] The method may further comprise heating the ceramic components whilst the interlayer is heated by passing through the electric current. For example, the ceramic components withthe interlayer provided therebetween may be heated in a heating chamber or furnace. Other options for heating the sample include laser heating, induction coil heating, infrared (IR) heating, microwave heating, radiofrequency (RF) heating, plasma heating, electron beam (e-beam) heating, and selective area heating techniques. The ceramic components may be heated to a temperature of less than 1600°C, preferably approximately 1000°C. This temperature may be less than the temperatures typically used in existing diffusion bonding processes of 1500°C to 2000°C, which can damage the SiC fibres in SiC / SiC composites that typically cannot withstand temperatures of greater than 1600°C for significant periods of time. In examples, the ceramic components may be heated to a temperature of between 800°C and 1600°C.

[0020] Advantageously, the method may be carried out in an extremely fast timescale, for example seconds-to-minutes and achieve near-seamless joints between the ceramic components. This means that the method has improved efficiency and saleability.

[0021] Advantageously, the comparably lower pressure required to provide for near-seamless joints between ceramic components using this method means that it is suitable for use on a large range of geometries, including, but not limited to, tubes, plates, panels, corners, complex shapes.

[0022] According to another aspect, there is provided an apparatus for joining ceramic components comprising a heating chamber / furnace arranged to receive a first ceramic component and a second ceramic components; and opposing electrodes arranged to resistively heat an interlayer provided between the first ceramic component and the second ceramic component to induce liquid-phase bonding, e.g. liquid phase diffusion bonding, between the first ceramic component and the second ceramic component. That is, the interlayer diffuses away.

[0023] The heating of the interlayer may be performed whilst the ceramic components and interlayer provided therebetween are heated in a heating chamber, or furnace. Pressure may be applied to the sample during heating. In such examples, the heating chamber or furnace may be provided as part of the apparatus. In examples, the heating chamber or furnace may be provided separately the apparatus. In examples, the pressure applied may be less than or equal to 10 MPa. In examples, the pressure applied may be less than 60MPa.

[0024] According to another aspect, there is provided an article formed according to the method of the above-described aspect.

[0025] According to another aspect, there is provided an article comprising a first ceramic component and a second ceramic component and a joint connecting the first ceramic component and second ceramic component, wherein the joint comprises the same material as the first and second ceramic components. In examples, there may be no interlayer left within the articlebetween the ceramic components. That is, in examples where the first and second ceramic components may be SiC, the joints may be SiC. That is, the joint may be purely SiC.

[0026] The article may be tubular in shape, as may be appropriate for e.g., containers, cooling tubes, projectile shells, and the like.

[0027] In examples, there is provided a nuclear fusion reactor comprising article formed according to the aforementioned method of joining ceramic components. In particular, the fusion reactor may comprise a vacuum vessel and a breeder blanket for the vacuum vessel, with the breeder blanket comprising joined ceramic components (for example SiC / SiC or another nonoxide ceramic matrix composite components). For example, the breeder blanket may comprise a flow channel comprising, or otherwise formed entirely from, ceramic components at least partially joined according to the above method.

[0028] In another aspect of the invention, there may be provided a fission reactor comprising components formed from ceramic components joined according to the aforementioned method. For example, fuel rods of the fission reactor may be clad with ceramic components at least partially joined according to the aforementioned method.

[0029] In another aspect of the invention, there may be provided an aerial vehicle comprising ceramic components joined according to the above method. For example, at least one of an airframe, nose-cone, and wings, may comprise, or be entirely formed from, ceramic components at least partially joined according to the above method. Moreover, internal components of the aerial vehicle may be formed wholly or partly ceramic components at least partially joined according to the above method, such as engine components.

[0030] Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.Brief Description of the Drawings

[0031] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which:

[0032] Figure 1 shows an example method of joining ceramic components;

[0033] Figure 2 is a diagram showing the method of figure 1 ;,

[0034] Figures 3a to 3c show scanning electron microscopy images of a part of an article formed according to the method of figure 1 , and / or using the apparatus of figure 2 - Fig. 3a shows a zoomed out view of an article, Fig. 3b shows a zoomed in view of the box 330 in Fig.3a, and Fig. 3c shows a zoomed in view of the box 340 in Fig. 3aDetailed Description

[0035] As shown in figure 1 , an example method 100 of joining ceramic components comprises, at step 102, providing an interlayer between a first ceramic component and a second ceramic component. The first and second ceramic components may be silicon carbide or silicon carbide fibre composites. The interlayer is electrically conductive, or can become conductive at increasing temperature, and may be a metal or metal oxide, such as yttrium, yttrium oxide, aluminium, aluminium oxide, chromium or chromium oxide. The interlayer may be a foil that is sandwiched between the first ceramic component and the second ceramic component. The interlayer may be a coating provided on at least one of the first ceramic component and the second ceramic component, for example by plasma vapour deposition. The interlayer may have a thickness of less than or equal to 25 microns. The interlayer may have a thickness greater than or equal to 100 nanometres.

[0036] The method comprises, at step 104, heating the interlayer by passing an electric current through the interlayer to melt the interlayer and induce liquid-phase diffusion bonding between the first ceramic component and the second ceramic component. Melting the interlayer may cause the interlayer material to dissipate through the first ceramic component and the second ceramic component.

[0037] The heating of the interlayer may be performed whilst the ceramic components and interlayer provided therebetween are heated in a heating chamber, or furnace, under pressure. The ceramic components may be heated to a temperature of greater than 800°C and less than 1600°C, preferably approximately 1000°C and the pressure applied may be less than or equal to 10 MPa.

[0038] The method uses the interlayer between the ceramic components (such as SiC or SiC / SiC) are directly-heated via resistive heating, i.e. via a current being passed through the material. The interlayer may be a coating or a foil. The interlayer may comprise a metallic material. For example, the interlayer may comprise a metallic coating or metallic foil. The interlayer may comprise rare-earth metals. The resistive heating local heating of the interlayer to high temperatures, causing the interlayer to melt. The resistive heating may be highly controllable via electrodes such thar the current passing though the interlayer is highly controllable.

[0039] In examples, the interlayer may comprise rare-earth metals, and these rare-earth metals melt. The molten interlayer (in examples, the molten rare-earth metals) provides a liquid phase for diffusion of SiC to occur, causing SiC atoms to re-arrange and bond with each other. The resultant joints are made of pure SiC. Advantageously the pure SiC joints provide the required high-temperature, creep and irradiation-resistance needed for fusion applications.

[0040] Figure 2 shows a diagram of an example apparatus 200 for carrying out the method of claim 1. As shown in Figure 2, the apparatus 100 comprises a heating chamber 220. The heating chamber 220 is arranged to receive a first ceramic component 204 and a second ceramic component 206. Opposing electrodes 208, 210 are arranged to pass a current through an interlayer 202 provided between the first ceramic component 204 and second ceramic component 206. This provides for resistive heating. This induces liquid-phase bonding between the first ceramic component 204 and second ceramic component 206. The electrodes 208, 210 may be arranged to pass current through the interlayer 202 in a highly controllable manner. The current passing through the electrode may be controlled based on the resistance in the interlayer 202.

[0041] As shown in figure 2, in use, an interlayer 202 is provided between two ceramic components 204, 206. In examples, the ceramic components are SiC / SiC fibre composite components 204, 206. The interlayer 202 may comprise a coating or a foil. The coating or foil may comprise a metallic material. The components 204, 206 with the interlayer 202 provided therebetween are heated in the heating chamber 220. In examples, the components 204, 206 are heated in the heating chamber 220 at approximately 1000°C. The electrodes 208, 210 are connected to the composite components 204, 206, and a current is passed through the composite components 204, 206. This melts the interlayer 202 and causes the diffusion of SiC between the two composite components 204, 206, thereby forming a near-seamless joint. In this way, the electrodes are connected to the composite components such that the current passing therethrough may be controlled. This means that current is not passed directly from the electrodes to the interlayer for better control of heating. The current may be highly controllable, to rapidly increase or decrease based on resistance.

[0042] Referring to figures 3a, 3b and 3c, a part of an article 300 formed according to the method of figure 1 , and / or using the apparatus of figure 2 is shown. These figures show a scanning electron microscopy images of a part of an article 300.

[0043] In examples, the article 300 may comprise a first ceramic component 302 and a second ceramic component 304. An interlayer 305 may be provided therebetween. This is shown in figure 3b.

[0044] Through the method of figure 1 and / or using the apparatus of figure 2, a joint 306 may be provided connecting the first ceramic component 302 and the second ceramic component 304.

[0045] The joint 306 may comprise the same material as the first 302 and second ceramic components 304. For example, each of the first ceramic component 302, the second ceramic component 304 and the join may comprise silicon carbide. As such, the joint 306 may be a nearseamless joint. This is shown in figure 3c.

[0046] In the specific example shown in figures 3a, an interlayer 305 consisting of 300nm yttrium may be deposited on one side of a SiC / SiC composite, also referred to as a first ceramic component 302. A second piece of a SiC / SiC composite, also referred to as a second ceramic component 304 may be placed on the opposing side of the interlayer 305. This means that the interlayer 305 may be provided between the first ceramic component 302 and the second ceramic component 304. The ceramic components 302, 304 and the interlayer 305 provided therebetween may be heated, as described in the method with reference to figure 1 . Specifically, in examples, the components 302, 304 and interlayer 305 may be heated in a furnace at between 800 and 1600°C.

[0047] Electrodes may be connected to the composite components 302, 304. A current may be passed through the composite components 302, 304 with a controlled amplitude for a controlled time. For example, a current of 10-A may be passed through the composite components 302, 304 for up to 120 seconds. In examples, a current greater than 10A may be used. In examples, a current of less than 10A may be used. In examples, the current may be passed through the composite components 302, 304 for a time less than or greater than 120s.

[0048] As shown in the scanning electron microscopy image in Fig. 3b, this may melt the interlayer 305, causing the interlayer 305 to diffuse away and into the composite components 302, 304, In examples this may cause the SiC grains to grow, or in other words diffuse, into the interlayer 304. This may also be referred to as liquid-phase diffusion.

[0049] As such, the interlayer 305 may form the joint 306. As shown in figure 3c, this may result in a near-seamless joint. As shown in 3c, the ceramic components 302, 304 to form a bonded component having the near seamless joint.

[0050] In examples, the heating chamber is also arranged to apply pressure during heating. In examples, the pressure applied may be less than or equal to 10 MPa.

[0051] Advantageously, the method described herein does not require substantial pressure changes. That is, the apparatus is not required to provide an environment with high pressure requirements. Typically, the pressure in the heating chamber may be less than or equal to 10MPa. This means that the apparatus is simplified, lower-cost and scalable for large industrial applications. Further, fewer environmental requirements are required to house the apparatus such that joined ceramic components may be locally produced on site.

[0052] Advantageously, the method described herein may be carried out at a significantly lower temperature as compared to existing methods for joining ceramic components. That is, the heating chamber of the apparatus is required to be heated to a much lower temperature than in existing arrangements. Inclusion of the electrodes for resistive heating of an interlayer, in order to induce liquid-phase bonding between ceramic components means that the heating chamber does not have to be heated to exceedingly high temperatures. This is particularly advantageous to minimise damage of SiC fibres that make-up SiC / SiC which must not be exposed to temperatures greater than 1600°C.

[0053] Further, using the method and apparatus described herein removes the requirement for highly-polished bonding surfaces. This means that effective bonding may be provided on lower quality surfaces, and preparatory steps may be removed. Advantageously, this means that the method and apparatus are suitable for the large scale of joining required for articles for a fusion reactor. For example, alternative methods may require compression of substrates or ceramic components as a preparatory step for bonding to occur. Advantageously, this is not required in the present invention, thereby improving efficiency of the method.

[0054] The apparatus and method are highly scalable for the requirements of joining for applications in a fusion reactor due to the simplified requirements of the apparatus.

[0055] Although the example embodiments have been described with reference to the components, modules and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of others.

[0056] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0057] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may becombined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0058] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0059] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS1. A method of joining ceramic components comprising:providing an interlayer between a first ceramic component and a second ceramic component, andheating the interlayer by passing an electric current through the interlayer to melt the interlayer and induce liquid-phase diffusion bonding between the first ceramic component and the second ceramic component.

2. The method of claim 1 , wherein the interlayer is a foil.

3. The method of claim 1, wherein the interlayer is a coating, and wherein providing the interlayer comprises applying a coating to at least one of the first ceramic component and the second ceramic component.

4. The method of claim 3, wherein applying the coating comprises applying the coating by plasma vapour deposition.

5. The method of any preceding claim, wherein the thickness of the interlayer is less than or equal to 25 microns.

6. The method of any preceding claim, wherein the thickness of the interlayer is greater than or equal to 100 nanometres.

7. The method of any preceding claim, wherein the interlayer is a metal or metal oxide.

8. The method of claim 7, wherein the interlayer is a rare earth metal or rare earth metal oxide.

9. The method of claim 7, wherein the interlayer comprises at least one of yttrium, yttrium oxide, aluminium, aluminium oxide, chromium and chromium oxide.

10. The method of any preceding claim, wherein the first and second ceramic components comprise silicon carbide.

11. The method of claim 10, wherein the first and second ceramic components comprise a silicon carbide fibre composite.

12. The method of any preceding claim, comprising applying pressure to the components while heating the interlayer.

13. The method, wherein applying pressure comprises applying pressure less than or equal to 10 MPa.

14. An article formed according to any the method of any preceding claim.

15. An article comprising a first ceramic component and a second ceramic component and a joint connecting the first ceramic component and second ceramic component, wherein the joint comprises the same material as the first and second ceramic components.

16. The article of claim 15, wherein the first and second ceramic components comprise silicon carbide or a silicon carbide fibre composite and wherein the joint is formed of silicon carbide.

17. A nuclear fusion reactor comprising the article of any of claims 14 to 16.

18. An apparatus for joining ceramic components comprising:a heating chamber arranged to receive and heat a first ceramic component and a second ceramic component; andopposing electrodes arranged to resistively heat an interlayer provided between the first ceramic component and the second ceramic component to induce liquid-phase bonding between the first ceramic component and the second ceramic component.

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