FIELD OF THE INVENTION

[0001] The invention relates to a composite structure. In particular, the invention relates, but is not limited, to a metallised or plasticised composite structure. The invention also relates to a method for producing a composite structure.

BACKGROUND TO THE INVENTION

[0002] Reference to background art herein is not to be construed as an admission that such art constitutes common general knowledge in Australia or elsewhere.

[0003] There is an ever-growing pursuit to develop new materials to meet consumer demands. One area of rapid development includes advanced composite materials. By way of example, a fibre-reinforced polymer (FRP), including a carbon fibre reinforced polymer (CFRP) (also known as carbon fibre reinforced plastics), are composite materials made up of a polymer matrix and reinforcing fibres. FRPs are commonly used in the aerospace, automotive, wind mills for renewable energy, marine and construction industries. FRPs can be designed and produced to have excellent mechanical and physical properties, such as high tensile strength, high torsional strength and low density.

[0004] Composite materials derived from epoxy resin and carbon fibres (such as CFRPs) are being extensively employed in aircraft industries because of their strength, high modulus and light weight. CFRPs offer their greatest advantage over isotropic materials when their fibre axes are aligned in the direction of principal stress. CFRPs and hybrid composites out perform their aluminium counterparts in terms of low weight for a required stiffness or strength (bearing in mind that the weight reduction with hybrid composites is not as great as for CFRP composites). Accordingly, engineers in many fields have turned to CFRPs to design stiff light weight structures.

[0005] More broadly, some FRPs feature a multitude of materials, whereby the different materials remain physically and chemically separate and distinct within the finished structure giving the finished structure its strength and rigidity. However, as the composite structure is a matrix of separate materials, it causes the potential for stress fatigue cracking and catastrophic structural failure. The aerospace industry has developed methods for the inspection and repair of carbon fibre composite structures for hairline cracks around fastener holes and cracks in high stress areas. These are of great concern as they are fatigue driven and, if not detected and corrected, could potentially affect the structural integrity of the aircraft.

[0006] Another potential downside of FRPs is that the external surfaces thereof tend to have low wear resistance. As a result, for certain applications, some form of surface modification is required. This may involve providing a wear-resistant layer on surfaces of the FRP. For instance, FRP aircraft wings and tail components are manufactured with a metallic layer on the surface (for example in the region of the leading edges) to prevent erosion. This metallic surface layer is commonly fabricated from metal sheet and/or billet and rivetted or glued to the FRP (or the underlying metal structure). By way of example, the joining of aluminium alloys and CFRP composites in aerospace structures is currently done by mechanical fasteners. Where high unaccounted loads are applied to the fasteners during assembly, they will combine with the stresses arising from the interference fit, potentially leading to cracking. The particular type of aluminium alloy used will also affect this joint behaviour where a balance has to be achieved between stiffness, strength and fracture toughness.

[0007] Another problem associated with FRP composite structures is the problem of surface finish quality of the moulded structure, as the physically and chemically separate materials create a bleed through effect of the fibre pattern through the cured polymer resin. To correct surface imperfections from the moulding process requires extensive manual finishing by grinding, sanding, filling and painting of the FRP composite structures.

[0008] With the above in mind, the efficient design of structures requires a detailed understanding of the fracture behaviour of the material and the modes of failure of the component, knowledge which is also necessary for the airworthiness flight clearance and the post-mortem examination of failed components. The fractography of different CFRP unidirectional (UD) or multidirectional (MD) composite materials has been the subject of studies by many investigators over the last four decades and some specific fractographic characteristics have been identified. Flowever, the results from composite fractography is not as mature as the fractographic analysis of surface morphology of metal components, but there is tremendous scope to bring composites fractography to the level of maturity akin to that of isotropic materials.

[0009] In order to assist with addressing some of the above problems, various approaches are used to provide a metallic layer on the surface of (amongst other things) an FRP structure. Some of these involve thermal spray deposition processes in which a metal in the form of powder, wire or rod is heated to near or slightly above its melting point and droplets of the metal are accelerated in a gas stream. The droplets are directed against a surface to be coated. A wide variety of metallic coatings can be produced using thermal spray deposition. However, being a high-temperature process, damage to the FRP surface being sprayed can occur. Furthermore, de lamination of the metal coating can arise due to poor adhesion of the metallic coating to the FRP composite structures. It may be possible to improve adhesion by roughening the surface of the FRP composite structures prior to thermal spraying (e.g., by grit blasting etc.). This itself can be undesirable though, because it can cause erosion of the polymer matrix and/or fraying of the fibres.

[0010] Several other techniques for preparing the surface of a FRP structure for thermal spraying have been tried, but these have not addressed the adhesion problem satisfactorily and/or are not viable to employ on a commercial scale. For example, one approach involves laminating a three-dimensional wire mat into the FRP structure followed by grit blasting to expose the wire and then thermal spraying. This approach is likely to be impractical to employ on a commercial scale.

[0011] Other efforts have focused on the use of cold-gas dynamic spraying (also known simply as 'cold spray') to provide a metal coating directly onto the surface of a FRP structure. Cold spray (or supersonic particle deposition) involves accelerating metal particles to a very high velocity, in a supersonic gas jet, which are then directed onto a substrate. On impact with the substrate, the particles undergo plastic deformation and adhere to the substrate surface. Unlike thermal spraying techniques, supersonic particle deposition does not involve melting material during the spraying process. This is beneficial when coating a thermally sensitive substrate such as a FRP. Flowever, depending upon the relative hardness of the material being sprayed, and the polymer matrix and fibres, erosion of the matrix and/or fraying of the fibres can still occur. Furthermore, delamination of the metal coating can arise due to poor adhesion of the coating to the composite structure. Efforts to address this issue have involved application of various primer coatings to the surface of the FRP structure before spraying. Flowever, this can bring with it compatibility and adhesion problems primarily from residual stresses, and add to the overall complexity of manufacture. Furthermore, consideration of using plastics with an FRP structure have been given limited attention, potentially due to compatibility and structural issues.

[0012] The present inventors have developed an improved composite structure and process for the production thereof.

SUMMARY OF INVENTION

[0013] In one form, although not necessarily the only or broadest form, the invention resides in a process for producing a composite structure, the process including: providing one or more fibres to a mould surface such that the one or more fibres are positioned to interact with a binder composition coated on at least part of the mould surface, the binder composition comprising a coupling agent and binder particles; and curing a polymer applied to the one or more fibres, wherein the coupling agent binds the polymer and the binder particles to form a bonding surface region as part of the composite structure.

[0014] In an embodiment, the binder particles are in a solid state.

[0015] In an embodiment, the binder particles are metallic, plastic or a mixture of both.

[0016] In an embodiment, the binder particles are visible to a human eye.

[0017] In an embodiment, the binder particles are specks. [0018] In an embodiment, the bonding surface region is a metallised surface region, plasticised surface region or a mixture of both.

[0019] In an embodiment, the binder may be sprayed or brushed onto the mould surface, or the mould surface may be coated with the binder composition, e.g., by dipping it into or otherwise contacting the mould surface with the binder composition.

[0020] In an embodiment, the process further comprises removing the composite structure from the mould.

[0021] In an embodiment, to facilitate removal of the composite structure from the mould, a mould release agent or a non-stick coating may be applied to the mould surface prior to applying the binder composition.

[0022] In an embodiment, the process further comprises applying one or more metallic coating(s) to the bonding surface region to form a coated composite structure.

[0023] In an embodiment, the step of applying the one or more metallic coating(s) to the bonding surface region includes applying the metallic coating(s) by supersonic particle deposition.

[0024] In an embodiment, the supersonic particle deposition comprises cold-gas dynamic spraying (also referred to herein as 'cold spraying' or 'cold spray').

[0025] In an embodiment, prior to the step of applying the metallic coating to the bonding surface region by supersonic particle deposition, the metallic particles in the metallised surface region are treated to reduce metal oxides to improve adhesion of the metal coat.

[0026] In an embodiment, the process further comprises applying one or more plastic coating(s) to the bonding surface region to form a coated composite structure.

[0027] In an embodiment, the step of applying the one or more plastic coating(s) to the bonding surface region includes applying the plastic coating(s) by supersonic particle deposition.

[0028] In an embodiment, prior to the step of applying the plastic coating to the bonding surface region by supersonic particle deposition, the plastic particles are treated to increase surface adhesion of the plastic coat.

[0029] In an embodiment, the process includes contacting the one or more fibres with the polymer before the polymer is cured. In a further embodiment, the one or more fibres are pre-impregnated with the polymer.

[0030] In an embodiment, the step of allowing the polymer to cure comprises the use of heat, pressure, UV, or a combination of any two or more thereof.

[0031 ] In an embodiment, the step of curing the polymer includes allowing the polymer to set in order to substantially lock the one or more fibres in place. [0032] In an embodiment, the process further comprises curing the binder composition. In an embodiment, the binder composition is cured prior to the addition of the one or more fibres.

[0033] In an embodiment, the coupling agent is capable of bonding organic materials, inorganic materials, or both organic or inorganic materials. In a preferred embodiment, the coupling agent is capable of binding both organic and inorganic materials. In an embodiment, in the step of providing the one or more fibres to the mould surface, the coupling agent comprises one or more functional groups capable of forming bonds with the polymer, the one or more fibres, or the metallic particles, or any combination of two or more thereof.

[0034] In an embodiment, the step of applying the one or more metallic coating(s) to the bonding surface region includes the coupling agent promoting adhesion of the metallic particles in the metallised surface region to the metallic coating, for example, by mitigating interference from metal surface oxides.

[0035] In an embodiment, in the step of providing the one or more fibres to a mould surface such that the one or more fibres are positioned to interact with a binder composition, the coupling agent comprises one or more functional group(s) selected from hydroxyl, amino, thiol, phosphate, epoxide, methacrylate, glycidyl, glycidyl methacrylate, an acrylic group, alkyl halide, isocyanate, hydrazide, semicarbazide, azide, an ester, a carboxylic acid, an aldehyde, a ketone, a vinyl group, and disulfide.

[0036] In an embodiment, in the step of providing the one or more fibres to a mould surface such that the one or more fibres are positioned to interact with a binder composition, the coupling agent comprises a silane coupling agent. In an embodiment, the silane coupling agent is an alkoxysilane. Silane coupling agents are well known in the art and are described, for example, by Peter G. Pape, in Applied Plastics Engineering Handbook (Second Edition), 2017 and Silane Coupling Agents. Plueddemann, Edwin P. (1982). Springer Science+Business Media LLC. Commercially available silane coupling reagents are available, for example, from Dow Corning or Gelest, Inc (see, for instance, https://www.gelest.com/wp- content/uploads/Silane_Coupling_Agents.pdf). Exemplary coupling silane coupling agents (such as 3-glycidoxypropyltrialkoxysilane, e.g., 3-glycidoxypropyltrimethoxysilane, N-(3-triethoxysilylpropyl)- 4,5-dihydroimidazole 3-(2-imidazolin-1-yl) propyltriethoxysilane, Bis(3- trimethoxysilylpropyl)fumarate, trimethoxysilylpropyl modified polyethyleneinimine, among others).

[0037] The selection of an appropriate coupling agent for a particular metal or plastic is within the ordinary skill of those skilled in the field. For example, titanium may be suited to silane coupling agents with epoxy or hydride functionality; copper and zinc may be suited to functionalised polyamine silanes, such polyethyleneimine silanes; iron may be suited to amine and sulfur functionalised silanes.

[0038] In an embodiment, the step of applying the one or more metallic coating(s) to the bonding surface region includes providing metallic particles of a single metallic species or a mixture of metallic species.

[0039] In an embodiment, in the step of applying the one or more metallic coating(s) to the metallised surface region the metallic particles comprise titanium, titanium alloys, aluminium, aluminium alloys, stainless steel, copper, copper alloys, zinc, tin, nickel, nickel alloys, niobium, niobium alloys, tantalum, tantalum alloys, metal matrix composite (MMC), and/or heterogeneous materials, or a combination of any two or more thereof.

[0040] In an embodiment, the step of applying the one or more plastic coating(s) to the bonding surface region includes providing plastic particles of a single plastic species or a mixture of plastic species.

[0041] In an embodiment, the plastic particles includes thermoplastic polymer. In an embodiment, the plastic particles include a polyether. In an embodiment, the plastic particles include a polyether ether ketone.

[0042] In an embodiment, the step of applying the one or more metallic coating(s) to the metallised surface region includes providing metallic particles in a size range of superfine 1 -500 microns in irregular or spherical morphology or a combination of both.

[0043] In an embodiment, the step of applying the one or more plastic coating(s) to the plasticised surface region includes providing plastic particles in a size range of superfine 1 -500 microns in irregular or spherical morphology or a combination of both.

[0044] In an embodiment, the process includes modifying the viscosity of the binder composition based on the amount or proportion of binder particles and/or the coupling agent.

[0045] In an embodiment, the step of curing the polymer that is applied to the one or more fibres includes curing a thermosetting or thermoplastic polymer.

[0046] In an embodiment, the step of curing the polymer that is applied to the one or more fibres includes the use of heat, pressure, ultraviolet (UV) light, or a combination of any two or more thereof. In a preferred embodiment, the curing step includes the use of UV light.

[0047] In an embodiment, the process further includes applying one or more finishing treatments to the one or more metallic or plastic coating(s).

[0048] In an embodiment, the invention resides in a composite structure prepared according to the processes described herein.

[0049] In another form, the invention resides in a process for producing a coated composite structure having a metallised surface region, the process comprising: providing one or more fibres to a mould surface such that the one or more fibres are positioned to interact with a binder composition comprising binder particles; curing a polymer applied to the one or more fibres, wherein the binder composition binds with the polymer to form a bonding surface region of a composite structure; and applying one or more coating(s) to the bonding surface region, wherein the one or more coating(s) is applied onto metallised surface region by supersonic particle deposition.

[0050] In accordance with the present invention, the expression 'bonding surface region' refers to the parts or areas (regions or loci) of the composite structure where the binder particles are located or positioned. The bonding surface region may comprise the whole or one or more parts or areas (regions or loci) of the composite structure.

[0051] In an embodiment, the binder particles are in a solid state.

[0052] In an embodiment, the binder particles are metallic, plastic or a mixture of both.

[0053] In an embodiment, the bonding surface region is a metallised surface region, plasticised surface region or a mixture of both.

[0054] In an embodiment, the one or more coating(s) is a metallic coating.

[0055] In an embodiment, the one or more coating(s) is a plastic coating

[0056] In an embodiment, the one or more metallic or plastic coating(s) includes an enhancing additive which may improve or enhance one or more properties of the composite structure, including for example, mechanical properties such as ductility, tensile strength.

[0057] In an embodiment, the enhancing additive includes a tannin compound, a lignin compound or a combination of any two or more thereof.

[0058] In an embodiment the enhancing additive, such as tannin or lignin, facilitates the supersonic particle deposition.

[0059] In an embodiment, the supersonic particle deposition comprises cold-gas dynamic spraying.

[0060] In an embodiment, the invention resides in a coated composite structure prepared according to the processes described herein.

[0061] In a further form, the invention resides in a method for repairing or reconditioning a coated composite structure, wherein the coated composite structure comprises a polymer reinforced with one or more fibres to form a surface, a bonding surface region and a coating on the bonding surface region, the method including: applying a further coating on: the bonding surface region; and the coating that is, at least in part, damaged or worn, to repair the composite structure, wherein the further coating is applied by supersonic particle deposition.

[0062] In an embodiment the method further includes retrieving the composite structure from an in use location prior to application of the further coating.

[0063] In another form, the invention resides in a composite structure having a bonding surface region formed during a moulding process, wherein the bonding surface region includes binder particles and a coupling agent that are coated on at least part of a mould surface that assists in forming a cured shape of the composite structure.

[0064] In an embodiment, the binder particles are in a solid state.

[0065] In an embodiment, the binder particles are metallic, plastic or a mixture of both.

[0066] In an embodiment, the bonding surface region is a metallised surface region, plasticised surface region or a mixture of both.

[0067] In an embodiment, the composite structure includes a polymer reinforced with one or more fibres.

[0068] In an embodiment, in response to the polymer being applied to the one or more fibres and cured, the coupling agent bonds the binder particles to the polymer to form the bonding surface region.

[0069] In an embodiment, the binder particles are bonded to the polymer at least in part by being mechanically or physically restrained in a matrix of the polymer.

[0070] In an embodiment, the binder particles are chemically bonded to the polymer.

[0071] In an embodiment, the bonding surface region assists in protecting the polymer reinforced with one or more fibres.

[0072] In an embodiment, the binder particles are harder than the polymer and/or coupling agent.

[0073] In an embodiment, the binder particles assist in protecting the polymer reinforced with one or more fibres.

[0074] In an embodiment, the bonding surface region directly engages to the polymer reinforced with the one or more fibres.

[0075] In an embodiment, the coupling agent comprises one or more functional groups capable of forming bonds with one or more of the polymer, the fibres, and the metallic particles.

[0076] In an embodiment, the coupling agent promotes adhesion of the binder particles in the bonding surface region to the coating by mitigating interference from (metal) surface oxides.

[0077] In an embodiment the coupling agent may be selected according to the nature of the binder particles.

[0078] In an embodiment, the coupling agent comprises one or more functional group(s) (G) selected from hydroxyl, amino (e.g., NH2, NHCi-6-alkyl, N(Ci-6-alkyl)2, thiol, phosphate, epoxide, methacrylate, glycidyl, glycidyl methacrylate, an acrylic group, C1-12 alkyl halide where the halide may be fluoro, chloro, bromo or iodo), isocyanate, hydrazide, semicarbazide, azide, an ester (e.g., Ci- ₆ alkylC(0)0Ci- ₆ alkyl), a carboxylic acid (e.g., Ci-i ₂ alkylC(0)0H), an aldehyde (e.g., Ci-i2alkylCH(0)), a ketone (e.g., Ci-6alkylC(0)Ci-6alkyl), a vinyl group, and disulfide.

[0079] In an embodiment, the coupling agent is a silane coupling agent. In an embodiment, the silane coupling agent is an alkoxysilane.

[0080] In an embodiment, the silane is an alkoxysilane selected from trialkoxysilane, a dialkoxysilane, a monoalkoxysilane, and a combination thereof, respectively represented by the following formulae (1 )-(18):

(R ¹ 0) ₃ Si(R ² -G) (1 ),

(R ¹ 0) ₂ Si(R ² )(R ³ G’) (2),

(R ¹ 0) ₂ Si(R ² G)(R ³ G’) (3),

(R ¹ 0)Si(R ² )(R ³ )(R ⁴ G) (4),

(R ¹ 0)Si(R ² )(R ³ G)(R ⁴ G’) (5),

(R ¹ 0)Si(R ² G)(R ³ G’)(R ⁴ G”) (6)

(R ¹ 0) ₃ Si-G (7),

(R ¹ 0) ₂ Si(R ² )(G) (8),

(R ¹ 0) ₂ Si(G)(G’) (9),

(R ¹ 0)Si(R ² )(R ³ )(G) (10),

(R ¹ 0)Si(R ² )(G)(G’) (11 ),

(R ¹ 0)Si(G)(G’)(G”) (12),

(R ¹ 0)sSi-(OG) (13),

(R ¹ 0) ₂ Si(R ² )(0G) (14),

(R ¹ 0) ₂ Si(OG)(OG') (15),

(R ¹ 0)Si(R ² )(R ³ )(0G) (16),

(R ¹ 0)Si(R ² )(OG)(OG') (17),

(R ¹ 0)Si(OG)(OG')(OG") (18), wherein each of R ¹ , R ² , R ³ and R ⁴ independently represents an organic group selected from C1-12 alkyl, C2-12 alkenyl, C5-10 aryl, and C ₃ -io carbocyclyl, each of G, G’, and G” is independently selected from a chemically feasible group appropriate to each instance selected from hydroxyl, amino (e.g., NH2, NHCi-6-alkyl, N(Ci-6-alkyl)2, thiol, phosphate, epoxide, a methacrylate group, a glycidyl group, a glycidyl methacrylate group, an acrylic group, C1-12 alkyl halide (where the halide may be fluoro, chloro, bromo or iodo), isocyanate, hydrazide, a semicarbazide, azide, an ester (e.g., Ci-6alkylC(0)0Ci-6alkyl), a carboxylic acid (e.g., Ci-i2alkylC(0)0H), an aldehyde (e.g., Ci-i2alkylCH(0)), a ketone (e.g., Ci-6alkylC(0)Ci-6alkyl), vinyl, and a disulfide.

[0081] In an embodiment, the coupling agent is in the form of a liquid, a solid (e.g., a powder), a gel, or an emulsion. In a preferred embodiment, the coupling agent is a liquid.

[0082] In an embodiment, the coupling agent is capable of solidifying upon drying.

[0083] In an embodiment, the binder particles may be a single species or a mixture of species.

[0084] In an embodiment, the metallic particles comprise titanium, titanium alloys, aluminium, aluminium alloys, stainless steel, copper, copper alloys, zinc, tin, nickel, nickel alloys, niobium, niobium alloys, tantalum, tantalum alloys, metal matrix composite (MMC), and/or heterogeneous materials or a combination of any two or more thereof.

[0085] In an embodiment, the plastic particles includes thermoplastic polymer. In an embodiment, the plastic particles include a polyether. In an embodiment, the plastic particles include a polyether ether ketone.

[0086] In an embodiment, the coupling agent in the binder composition ranges between approximately 5%wt binder particles to 95%wt coupling agent.

[0087] In an embodiment, the metallic particles in the binder composition ranges between approximately 5%wt binder particles to 95%wt coupling agent.

[0088] In an embodiment, the ratio of binder particles to coupling agent in the binder composition ranges between approximately 5%wt binder particles to 95%wt coupling agent to 95%wt binder particles to 5%wt coupling agent.

[0089] In an embodiment, the binder particles with the coupling agent includes the binder particles being diffused within the coupling agent.

[0090] In an embodiment, the binder particles and the coupling agent form at least part of a binder composition.

[0091] In an embodiment, the binder composition comprises a range of 60-80%wt binder particles to 20-40%wt coupling agent.

[0092] In an embodiment, the binder composition comprises at least 50%wt binder particles.

[0093] In an embodiment, the binder composition comprises at least 85%wt binder particles.

[0094] In an embodiment, the average particle size of the binder particles may be from 5-150 microns, for example from 15-45 microns. The particles may be spherical and/or non-spherical (e.g., in flake form).

[0095] In an embodiment, the metallic particles are processed in order to reduce oxidation.

[0096] In an embodiment, the binder particles are corona treated.

[0097] In an embodiment, the viscosity of the binder composition may be modified based on the amount or proportion of binder particles and/or the coupling agent. In another embodiment, the viscosity of the composition may be modified by the use of a rheology modifying additive.

[0098] In an embodiment, the binder composition may further comprise one or more additives capable of modifying one or more properties of the composite structure, such as surface hardness, electrical conductivity, thermal conductivity, mechanical strength, chemical resistance, aberration resistance and/or EMI shielding.

[0099] In an embodiment, the binder composition further comprises one or more additive(s) selected from graphene, carbon nanoparticles, e.g., nanographene, ceramics, silica, or a combination of any two or more thereof. In an embodiment, the additive is graphene. In an embodiment, the additive is carbon nanoparticles.

[00100] In an embodiment, the one or more fibres may be organic or inorganic. In an embodiment, the one or more fibres are carbon fibres, glass fibres, or a combination thereof. In an embodiment, the one or more fibres are carbon fibres.

[00101 ] In an embodiment, the one or more fibres are in mat form or preformed to a predetermined shape. In an embodiment, the predetermined shape substantially conforms to a mould surface.

[00102] In an embodiment, the polymer is a thermosetting polymer.

[00103] In an embodiment, the thermosetting polymer is selected from an epoxy resin, melamine formaldehyde, a polyester resin, urea formaldehyde, a vinyl ester, a phenolic resin, a polyurethane, a cyanate ester, a polyimide resin, a maleimide resin and a combination of any two or more thereof.

[00104] In an embodiment, forming the composite structure includes curing the polymer component. In an embodiment, the polymer includes a curing agent.

[00105] In an embodiment, curing facilitates binding of the polymer to the coupling agent.

[00106] In an embodiment, curing the polymer causes the one or more fibres to bond (e.g., by cross-linking) to at least part of the binder composition.

[00107] In an embodiment, the composite structure further comprises one or more coatings (which may also be referred to herein as metallic layers) on the bonding surface region.

[00108] In an embodiment, the or each coating is applied to the metallised surface region by supersonic particle deposition. In an embodiment, the metal coating composition includes an additive such as tannin or lignin which facilitates the supersonic particle deposition.

[00109] In an embodiment, the binder particles in the bonding surface region are treated to improve adhesion to the metallic coating(s).

[00110] In an embodiment, the coating is formed from two or more coats or layers. In an embodiment, the metallic or plastic coating is formed from two or more coats, wherein each coat may comprise the same or different metal or plastic, and each coat may be the same or different thickness.

[00111] In an embodiment, when multiple coatings are applied to the bonding surface region of the composite structure, the metal or the plastic used in each coating is the same. In an alternative embodiment, different metals or plastics may be used for each coating. In other embodiments, some coatings may comprise the same metal and/or plastic and other coatings may comprise a different metal and/or plastic.

[00112] In an embodiment, the material in the or each coating is the same as the binder particles. In an alternative embodiment, the material in the or each coating is different to the binder particles.

[00113] In an embodiment, the species used in at least one of the coating(s) is the same as the binder particles in the bonding surface region. In an alternative embodiment, the species used in at least one of the coating(s) is different to the binder particles in the bonding surface region.

[00114] In an embodiment, the metallic coating may comprise a single metallic species, or a mixture of metallic species, or a mixture of metallic and non-metallic species. In an embodiment, the metallic coating comprises one or more metals or metal alloys. For example, the metallic coating may comprise titanium, titanium alloys, aluminium, aluminium alloys, stainless steel, copper, copper alloys, zinc, tin, nickel, nickel alloys, niobium, niobium alloys, tantalum, tantalum alloys, metal matrix composite (MMC), and/or heterogeneous materials or a combination of any two or more thereof.

[00115] In an embodiment, the metallic or plastic particles in the bonding surface region strengthen and protect the surface of the composite structure. In an embodiment, the metallic or plastic particles assist in protecting the surface of the composite structure during the application of the coating via cold spray.

[00116] In an embodiment, the coating bonds with the coupling agent.

[00117] In an embodiment, the particles to be applied by supersonic particle deposition are in the form of a powder.

[00118] In an embodiment, the coating is formed from sprayed particles having a particle size from 0.5 to 500 microns. [00119] In an embodiment, the thickness of the coating is 5 miti to 100,000 miti or 0.005 mm to 100 mm.

[00120] In an embodiment, the coating comprises particles that are relatively hard compared to the binder particles in the binder composition to assist with bond strength therebetween.

[00121] In an embodiment, the metallic coating or the plastic coating is subjected to one or more finishing treatments.

[00122] In an embodiment, the invention resides in a coated composite structure as described herein.

[00123] In embodiments of the invention, the moulding process is the process for producing a composite structure having a metallised or plasticised surface region as disclosed herein, including all embodiments thereof.

[00124] In other embodiments of the invention, the moulding process is the process for producing a coated composite structure having a metallised or plasticised surface region as disclosed herein, including all embodiments thereof.

[00125] In a further form, the invention resides in a moulded composite structure having a bonding surface region formed by applying a binder composition to at least part of a mould surface for curing during the moulding process, the binder composition comprising a coupling agent and binder particles. In an embodiment, the moulded composite structure has a bonding surface region on both sides of the structure. In alternative embodiments, the moulded composite structure has a bonding surface region on one side of the structure.

[00126] In another form, the invention resides in a coated composite structure including: a polymer reinforced with one or more fibres to form a surface; one or more binder particles interacting with the surface on a mould to form a bonding surface region; and a coating on the bonding surface region, wherein the metallic coating is applied by supersonic particle deposition.

[00127] In an embodiment, the one or more binder particles form part of a binder composition.

[00128] In an embodiment, the binder composition further comprises a coupling agent. The coupling agent may bond to the binder particles, the polymer, or both.

[00129] In an embodiment, the polymer is cured with the binder particles to form the bonding surface region.

[00130] In an embodiment, the coated composite structure is as herein described.

[00131] Further features and advantages of the present invention will become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[00132] By way of example only, preferred embodiments of the invention will be described more fully with reference to the accompanying figures, wherein:

Figure 1 illustrates a composite structure, according to an embodiment of the invention;

Figure 2 illustrates a coated composite structure including the composite structure shown in Figure 1 including a metallic layer;

Figure 3 illustrates the coated composite structure shown in Figure 2 with a further metallic layer;

Figure 4 illustrates the composite structure shown in Figure 1 , in a layup tool having a mould surface, according to an embodiment of the invention;

Figure 5 illustrates a method of forming the coated composite structure shown in Figure 2, according to an embodiment of the invention;

Figure 6 illustrates a further method of forming a coated composite structure according to an embodiment of the invention;

Figure 7 illustrates a method of removing surface oxides from metal powders prior to mixing with a coupling agent prior to hermetically sealing for storage; and

Figure 8 illustrates a method of removing surface oxides from metal powders prior to mixing with graphene non particles and hermetically sealing for storage.

DETAILED DESCRIPTION OF THE DRAWINGS

[00133] Figure 1 illustrates a composite structure 10 in accordance with an embodiment of the invention. The composite structure 10 includes a polymer reinforced with one or more fibres, referred to herein as fibre-reinforced polymer (FRP) 20. The fibre-reinforced polymer 20 bonds to a binder composition. The binder composition assists in forming a bonding surface region in the form of metallised surface region 30 in this embodiment. Furthermore, as shown in Figure 2, the composite structure 10 may further include a metallic coating 40 to form a coated composite structure 10'. In further embodiments, a person skilled in the art would appreciate, based on the present disclosure, that the bonding surface region may be a plasticised surface region when plastic particles are used. However, the present description is directed towards a metallised surface region 30 and metallic coating 40.

[00134] The fibre-reinforced polymer 20 in the embodiment shown in Figures 1 and 2 includes fibres in the form of carbon fibre. The carbon fibre may take the form of a carbon fibre mat. In further embodiments, it will be appreciated that, for example, alternative fibres such as fibre glass and/or other like materials may be used. In this regard, the fibres may be organic or inorganic. The fibres may be in the form of 'dry' fibres to which a polymer is added, or prepreg having polymer resin already loaded among the fibres. As outlined in further detail below, in response to polymer being applied to the fibres, a coupling agent in the binder composition is configured to bond thereto to form the composite structure 10. That is, during curing of the polymer, the fibres / polymer matrix bond to or form cross links to the binder composition, e.g., the coupling agent in the binder composition, to form a very strong permanent (e.g., covalent) bond. The polymer in this embodiment is in the form of a thermosetting polymer known as an epoxy resin. However, other polymers may be used and in further embodiments, the polymer may be a melamine formaldehyde polymer, a polyester resin, urea formaldehyde polymer, a vinyl ester polymer, a phenolic resin, a polyurethane polymer, a cyanate ester polymer, a polyimide resin, a maleimide resin and/or a combination of any two or more thereof. The fibre-reinforced polymer 20 includes a surface 22 that is configured to interact and attach to the metallised surface region 30.

[00135] The metallised surface region 30 (comprising at least the binder composition) is configured to assist in protecting at least a portion of, substantially all of, or the entire surface 22 of the fibre-reinforced polymer 20 when the metallic coating 40 is applied. However, the metallised surface region 30 may have other functionality in its own right. As will be appreciated by a person skilled in the art, the binder composition will interact with and may penetrate the surface 22. Accordingly, the metallised surface region 30 will typically not be a separate sheet from the fibre- reinforced polymer 20 (in comparison to that shown in Figures 1 and 2). On this basis, the term surface includes, for example, a generally defined area where a part or component is located and it may be uneven, not continuous etc. A person skilled in the art would also appreciate that similar principles will apply in the bonding surface region is primarily a plasticised surface region using plastic binder particles.

[00136] The binder composition includes binder particles, in the form of metallic particles, distributed in a coupling agent. In further embodiments, the binder composition may include plastic particles instead of, or in addition to, the metallic particles.

[00137] The coupling agent comprises at least one functional group that is capable of forming one or more bonds with the polymer and/or the fibres of the fibre-reinforced polymer 20. Furthermore, the coupling agent comprises at least one functional group that is configured to form one or more bonds to the metallic particles within the binder composition. Based on the specific chemical nature of the fibre-reinforced polymer 20 and the metallic / plastic particles, a person skilled in the art would know and be able to select appropriate coupling agents for use in combination with the specific fibre-reinforced polymers and metallic / plastic particles to ensure the coupling agent can react with the polymer component of the fibre-reinforced polymer 20, the fibres of the fibre-reinforced polymer 20, the metallic / plastic particles within the binder composition, or any combination of two or more thereof. [00138] With the above in mind, depending on at least the nature of the fibre-reinforced polymer 20 and the metallic particles, the coupling agent may comprise one or more one functional group(s) selected from hydroxyl, amino, thiol, phosphate, epoxide, methacrylate, glycidyl, glycidyl, methacrylate, an acrylic group, alkyl halide, isocyanate, hydrazide, semicarbazide, azide, an ester, a carboxylic acid, an aldehyde, a ketone, vinyl, a disulphide, or any other suitable functional group.

[00139] In a preferred embodiment, the coupling agent is a silane coupling agent, such as an alkoxysilane. The alkoxysilane may be a compound that contains one to three organic groups covalently bonded to a silicon atom through an oxygen atom, and at least one to three groups of formula -R-G, G, or -O-G covalently bonded directly to the silicon atom, as appropriate such that the silicon atom is tetra-coordinated. In some embodiments, the alkoxysilane is selected from trialkoxysilanes, dialkoxysilanes, monoalkoxysilanes, and a combination thereof, respectively represented by the following formulae (1 )-(18):

(R ¹ 0) ₃ Si(R ² -G) (1 ),

(R ¹ 0)2Si(R ² )(R ³ G’) (2),

(R ¹ 0) ₂ Si(R ² G)(R ³ G’) (3),

(R ¹ 0)Si(R ² )(R ³ )(R ⁴ G) (4),

(R ¹ 0)Si(R ² )(R ³ G)(R ⁴ G’) (5),

(R ¹ 0)Si(R ² G)(R ³ G’)(R ⁴ G”) (6)

(R ¹ 0) ₃ Si-G (7),

(R ¹ 0) ₂ Si(R ² )(G’) (8),

(R ¹ 0) ₂ Si(G)(G’) (9),

(R ¹ 0)Si(R ² )(R ³ )(G) (10),

(R ¹ 0)Si(R ² )(G)(G’) (11 ),

(R ¹ 0)Si(G)(G’)(G”) (12),

(R ¹ 0) ₃ Si-(OG) (13),

(R ¹ 0) ₂ Si(R ² )(0G’) (14),

(R ¹ 0) ₂ Si(OG)(OG’) (15),

(R ¹ 0)Si(R ² )(R ³ )(0G) (16),

(R ¹ 0)Si(R ² )(OG)(OG’) (17),

(R ¹ 0)Si(OG)(OG’)(OG”) (18), wherein: each of R ¹ , R ² , R ³ and R ⁴ independently represents an organic group selected from Ci-i ₂ alkyl, C2-12 alkenyl, C5-10 aryl, and C3-10 carbocyclyl, each of G, G’, and G” is independently selected from a chemically feasible group appropriate to each instance selected from hydroxyl, amino (e.g., NH2, NHCi e-alkyl, N(Ci-6-alkyl)2, thiol, phosphate, epoxide, a methacrylate group, a glycidyl group, a glycidyl methacrylate group, an acrylic group, C1-12 alkyl halide (where the halide may be fluoro, chloro, bromo or iodo), isocyanate, hydrazide, a semicarbazide, azide, an ester (e.g., Ci-6alkylC(0)0Ci-6alkyl), a carboxylic acid (e.g., Ci-i ₂ alkylC(0)0H), an aldehyde (e.g., Ci-i ₂ alkylCH(0), a ketone (e.g., Ci- ₆ alkylC(0)Ci- ₆ alkyl, vinyl, and a disulphide.

[00140] In some embodiments, R ¹ , R ² , R ³ and R ⁴ are the same organic group. In some embodiments, G, G’, and G” are the same functional moiety. In any case, the silane coupling agent in this embodiment is capable of coupling to the fibre-reinforced polymer 20 in the form of carbon fibre and titanium metallic particles. As outlined further below, the coupling agent in this embodiment is a liquid but, in further embodiments, the coupling agent may be a solid, e.g., a powder, granules or other suitable form such as a gel or emulsion. There is therefore no particular limitation on the coupling agent used, provided that it is capable of coupling to the metallic particles, fibre, polymer or any combination thereof.

[00141] In the embodiment shown in Figure 1 , the coupling agent used is a silane coupling agent, specifically 3-glycidoxypropyltrimethoxysilane (purchased from BF Speciality Chemicals). In further embodiments, the type of material (amongst other things) will guide what coupling agent is appropriate. Numerous coupling agents, including silane coupling agents, are commercially available, and include for example those listed at: https://www.gelest.com/wp- content/uploads/Silane_Coupling_Agents.pdf, the entire contents of which are hereby incorporated by cross reference.

[00142] Coupling agents are also described in B. Arkles et al. J Adhesion Science Technol. 2012, 26, 41 , P. Pape et al. in Silanes and Other Coupling Agents, ed. K Mittal, 1992 VSP, incorporated herein by cross reference.

[00143] The mechanism by which the binder metallic particles (or binder plastic particles) are bonded to the fibre-reinforced polymer 20 will depend on (amongst other things) the bonds capable of being formed by the coupling agent. In an embodiment in which the coupling agent bonds to the fibre reinforced polymer 20 but not the metallic particles, the metallic particles may be immobilised by being surrounded and trapped within a matrix of the coupling agent. In an embodiment in which the coupling agent bonds to the fibre-reinforced polymer 20 and the metallic particles, the bonding interactions involving the coupling agent may also contribute to the metallic particles being immobilised on the surface 22 of the fibre-reinforced polymer 20. To this end, the bonds of the metallic particles to the fibre-reinforced polymer 20 / coupling agent may be chemical in nature (ie, covalent bond, ionic bonds etc.) and/or mechanical in nature. [00144] The metallic particles used in the binder composition are selected based on the intended functionality of the metallised surface region in the composite structure 10. As noted above, the metallised surface region 30 may have functionality in its own right, without the addition of the metallic coating 40. The functionality of the metallised surface region 30 may include, for instance, the ability to engineer performance properties of dissimilar metals on non-metallic materials in specific zones or entire surfaces, to form electrically conductive EMF barrier sections, lightning strike plates, or to form smart sensory data collection material. The metallic particles in the metallised surface region 30 may be of a single metallic species or a mixture of metallic species, heterogeneous and/or homogeneous. Metals and metal alloys may be used including titanium, titanium alloys, aluminium, aluminium alloys, stainless steel, copper, copper alloys, zinc, tin, nickel, nickel alloys, niobium, niobium alloys, tantalum, tantalum alloys, metal matrix composite (MMC), and/or heterogeneous materials or a combination of any two or more thereof. The average particle size of the metallic particles may be from 5-150 microns, or more specifically from 15-45 microns. The particles may be spherical and/or non-spherical (e.g. in flake form). The metallic particles (or binder particles) have a higher relative hardness compared to the polymer or coupling agent. The binder particles may be a speck in the form of a powder, pellet or the alike.

[00145] The amount or proportion of metallic particles present in the binder composition is based on allowing, for example, sufficient anchoring points to obtain successful adhesion with the fibre-reinforced polymer 20 and/or the metallic layer 40. In some embodiments, the weight ratio of metallic particles to coupling agent ranges between 1% metallic particles to 99% coupling agent or 99% metallic particles to 1% coupling agent. The preferred range of metallic particles is 60%-85% to 20%-45% coupling agent. It will be appreciated that the content of metallic particles in the metallised surface region 30 may be lower than that in the coupling agent itself, for example when formation of the binder layer involves evaporation of one or more volatiles from the coupling agent used.

[00146] As will be outlined in further detail below, the metallic particles in the metallised surface region 30 are intended to allow the metallic coating 40 to be applied thereon, through supersonic particle deposition (eg, cold spray deposition), to create a strong bond therebetween whilst assisting in protecting the underlying fibre-reinforced polymer 20. The distribution and loading density of metallic particles in the metallised surface region 30 will influence its effectiveness in this regard. For example, if the loading density of the metallic particles is too low, metallised surface region 30 may not be suitable when supersonic particle deposition takes place with the result that damage occurs to the underlying fibre-reinforced polymer 20. A similar problem may occur if the distribution of metallic particles is wholly uneven and there are regions in the binder layer that are deficient or devoid of metallic particles.

[00147] The size distribution of metallic particles used for the metallised surface region 30 may also be significant on their effectiveness. In practice, the metallic particles used may comprise a range of particles sizes and this could be beneficial since close packing of particles (smaller particles in interstitial spaces between larger particles) is then possible. This will minimise the dimension of particle free regions in the metallised surface region 30. The morphology of the metallic particles may also be influential. The particles may have the same overall morphology, or a blend of morphologies may be used, for example a blend of spherical and flake particles.

[00148] The thickness and viscosity of the binder composition forming the metallised surface region 30 will also influence its efficacy. In principle, shielding of the fibre-reinforced polymer 20 by the metallised surface region 30 may be achieved using a layer thickness having a monolayer of metallic particles. In practice however, the metallised surface region 30 is likely to have a greater thickness with metallic particles distributed through its thickness/depth. This is likely to be beneficial since it will minimise or prevent the possibility of supersonic particles travelling through the metallised surface region 30 without contacting metallic particles in the binder composition. The thickness of the metallised surface region 30 used will also depend upon various other factors, including the rheology of the binder composition / coupling agent used, adhesion promoter, the loading density of metallic and non-particles particles and the methodology by which the metallised surface region 30 is formed on a surface of the mould / layup tool. Typically, the metallised surface region 30 thickness will be from 0.01 mm. to 10 mm, for example, from 0.05 mm. to 2 mm.

[00149] The metallised surface region 30 may also include additives to provide enhanced properties. For example, further enhanced surface hardness may be achieved by providing particles such as silica, ceramics, and/or carbon nanotubes and graphene in the binder layer to enhance electrical, or thermal conductivity, mechanical strength, chemical resistance, aberration resistance or EMI shielding. In this embodiment however, the metallised surface region 30 is intended to facilitate deposition of a metallic coating 40 thereover by supersonic particle deposition (ie, cold spray), and it is the cold sprayed metallic coating that assists in providing a specific functionality to the coated composite structure 10'.

[00150] As noted above, the metallic coating 40 in this embodiment is in the form of titanium that is deposited via supersonic particle deposition. As shown in Figure 3, it may also be advantageous to add further metallic layer(s) 50 to achieve other specific properties (eg, thermal conductivity, hardness etc.). During supersonic particle deposition, particles are accelerated in a supersonic gas jet to a high velocity (typically 500 to 1000 m/s). In response to the particles impacting a substrate, they undergo plastic deformation and adhere to the substrate. It is known that various factors influence the adhesive strength of cold spray coatings including the relative hardness of the particles and substrate used, the deposition velocity and the gas used.

[00151] In this embodiment, the metallic particles present in the metallised surface region 30 are the same type as the metallic particles being deposited by supersonic particle deposition for the metallic coating 40. That is, both are titanium. In further embodiments, the metallic particles present in the metallised surface region 30 may be different from the metallic particles being deposited by supersonic particle deposition. In these further embodiments, the relative hardness of the metallic particles used is likely to influence the adhesive strength of the deposited coating to the metallised surface region 30. In particular, a higher adhesive bond strength may be obtained by supersonic particle deposition of relatively hard particles onto a metallised surface region 30 that comprises relatively soft metallic particles.

[00152] The metallic particles of the metallic coating 40 may be of a single metallic species or a mixture of metallic and non-metallic species. For example, in addition to titanium, other metals/metal alloys that may be used include titanium, titanium alloys, aluminium, aluminium alloys, stainless steel, copper, copper alloys, zinc, tin, nickel, nickel alloys, niobium, niobium alloys, tantalum, tantalum alloys, metal matrix composite (MMC), and/or heterogeneous materials or a combination of any two or more thereof. The average particle size of the sprayed metallic particles may be from 5 to 500 microns, for example, from 15 to 45 microns. The particles may be spherical and/or non-spherical (e.g. in flake form). The thickness of the metallic coating 40 is typically 10 pm to 100,000 pm or 0.01 mm - 100 mm. With titanium used in the present embodiment, it is intended to provide wear resistance to the fibre-reinforced polymer 20. The metallic coating deposited by supersonic particle deposition may be subjected to one or more finishing treatments, such as shot peening, polishing and painting. The metallic coating may also be subjected to tempering, residual stress / heat treatment or hot isostatic pressing treatment. In addition, the metallic coating 40 may also include an enhancing additive. For example, the metallic coating 40 may include enhancing additives such as a tannin or lignin. More specifically, a tannin compound, mixed with a metallic species, may result in a metallic coating 40 that is more elastic or has improved ductility compared to applying a metallic species alone.

[00153] Figure 4 illustrates the composite structure 10, shown in Figure 1 , in a layup tool 100 having a mould surface 110. It will be appreciated that the tool 100 may be a female mould, a male mould or a mould that comprises top and bottom (or left and right) parts. The tool 100 will be formed of usual materials such as stainless steel or Fe-Ni alloy (eg, Invar, Nickel, Nickel Alloys, tooling steel) or from plastics, FRP, wood or composite wood materials such as MDF.

[00154] Figure 5 illustrates a method 1000 of forming the coated composite structure 10', shown in Figure 2, which will be further discussed below.

[00155] At the outset, the tool 100 is coated with a release agent at step 1100. This release agent allows the metallised composite 10, shown in Figure 1 , to be released after it is cured. At step 1200, which may be carried out before, after or concurrently with step 1100, the coupling agent (ie, alkoxysilane) is mixed with the metallic particles (ie, titanium powder) to form a binder composition. In further embodiments, it will be appreciated that plastic particles (eg, PEEK) can be mixed with the coupling agent. When the coupling agent is a liquid, the binder will take the form of a slurry/suspension of metallic particles distributed in the coupling agent. In further embodiments, TiCP particles of size range 5 to 45 micron may be combined with the silane coupling agent using an augur mixer and the mixture is treated in a vacuum chamber removing all trapped air bubbles.

[00156] At step 1300, the mould surface 110 of the tool 100 is coated with the binder composition to assist in forming the metallised surface region 30. As the binder composition is cured at step 1400, the metallised surface region 30 is substantially formed and somewhat takes the shape of a layer. Curing takes place by evaporating one or more volatile compounds from the coupling agent. It is possible that the coupling agent may bond to the material from which the tool 100 is formed. This may be tolerated provided it does not cause any issues when it is desired to remove the metallised compositelO, shown in Figure 1 , from the tool 100 or problems with the integrity of the metallised surface region 30.

[00157] The metallised surface region 30 (or plasticised surface regions in other embodiments) may be provided on the mould surface 110 by a variety of techniques depending upon the physical state of the coupling agent used. When the coupling agent is a liquid, the binder composition may be sprayed or brushed onto the mould surface 110 or the mould surface 110 may be coated by dipping it into the binder composition.

[00158] After application to the mould surface 110, it is important that the binder composition remains in place prior to drying / curing. This can be difficult depending upon the profile of the mould surface 110. It may be desirable to use a highly viscous (non-flowable) binder composition. This may be achieved by adjusting the density of metallic particles in the coupling agent or by use of a rheology modifying additive to influence the viscosity of the binder layer formulation. In another embodiment, it may be possible to minimise flow by rapid drying or curing of the coupling agent after application of the binder composition to the mould surface 110. Application of the binder composition to a heated mould surface may also facilitate this.

[00159] In an alternative approach, a liquid coupling agent may be applied to the mould surface 110 and then metallic particles delivered into/onto the coupling agent to form the binder composition in situ, followed by drying or curing of the coupling agent. Similar considerations will apply with respect to the rheology characteristics of the coupling agent so that it is retained at desired locations of the mould surface 110 prior to being fixed by drying/curing. In this alternative approach, partial drying/curing of the liquid coupling agent may take place before delivery of metallic particles into/onto the coupling agent. To this end, it may be desirable to repeat at least application of the coupling agent to produce a binder layer with metallic particles completely embedded in it.

[00160] In another embodiment, the coupling agent may be in the form of a gel and the methodology for application to a mould surface will be chosen accordingly. Furthermore, for other embodiments, the coupling agent may be a solid. In this case, the coupling agent in powder/particulate form may be blended with metallic particles and the blend formulation applied to the mould surface 110. The coupling agent may then be cured or activated to fix it and thus the metallic particles on the mould surface 110. This is a powder coat type methodology.

[00161 ] Of the various approaches for forming the binder composition described, application to a mould surface of a slurry/suspension of metallic particles in a liquid coupling agent may be preferable because this will result in intimate mixing of the metallic particles and the coupling agent and therefore enhanced bonding/retention of metallic particles in the coupling agent. Furthermore, as the metallised surface region 30 may only be required in certain locations of the mould surface 110, for a desired functionality, this may also affect the approach taken in forming the metallised surface region 30. For example, the metallised surface region 30 may only be required on a leading edge of a tail piece where erosion resistance is required.

[00162] At step 1500, the one or more (carbon) fibres are laid over the metallised surface region 30. In this embodiment, the one or more (carbon) fibres include the polymer therein and, as such, a 'prepreg' lay up is carried out. Accordingly, at step 1600, the tool 100 etc. is bagged and pressure / heat is applied to cure the fibre-reinforced polymer 20 at step 1700. During curing, cross links form between the fibre-reinforced polymer 20 to the underlying coupling agent making a very strong permanent bond, e.g., a covalent bond. This in turn couples permanently to the metallic particles contained therein. Thereafter, the composite structure 10, shown in Figure 1 , is released from the moulding surface 110 at step 1800. It may be possible to separate the composite structure 10 from the mould by application of a mechanical force, by injecting fluid (eg, air) between the mould surface 110 / metallised surface region 30 or by relying on differences in coefficient of thermal expansion as between the mould material, metallised surface region 30 and fibre-reinforce polymer 20. It may also be desirable to use a mould release agent on the mould prior to application of the binder composition.

[00163] At step 1900, supersonic particle deposition is used to apply the metallic coating 40 onto the metallised surface region 30. As indicated above, metallic powder in the form of titanium is accelerated in a supersonic gas jet to high velocity (typically 500 to 1000 m/s) and impacts the metallised surface region 30. The process gas pressure may be between 3 to 12 MPA and temperature can be varied in range of 500 to 1300°C. In further embodiments, the sprayed coating may vary in compositional mix of more than one type of particles such that the composition of mix of particles is continuously varied from start of spray till end of spray. The coating may also be formed of plastic powder. . Once the supersonic spraying is complete, some post processing procedures may be undertaken before the coated composite 10' is put into use.

[00164] To this end, whilst the composite structure 10' is in use, it may require repair due to (amongst other things) corrosion and erosion, crack surface irregularities, wear and so forth. On this basis, the coated composite 10' has the advantage that it can be recoated with a further metallic coating to repair the coated composite 10'. That is, further metallic powder may be sprayed onto the metallised surface region 30 in response to degradation of the metallic coating 40. This extends the service life of the coated composite 10' and reduces ongoing costs.

[00165] Figure 6 illustrates a further method 1000' of producing a metallised composite. As will be appreciated from Figure 6, the method 1000 is substantially the same as method 1000, but dry fibres are used at step 1500' instead of 'prepreg'. On this basis, method 1000' requires the polymer (ie, resin) to be infused into the fibres / metallised surface region 30 at step 1650'. Accordingly, it will be appreciated that a number of moulding process could be used in the present invention including bladder moulding, autoclave, compression moulding, vacuum infusion moulding, vacuum bagging, wet lay-up and resin transfer moulding. These processes may be manual or semi or fully automated.

[00166] With the above in mind, one challenge with using titanium and other reactive and refractory metals in the binder composition is that it tends to oxidise readily. High levels of oxides can interfere with (amongst other things) metallic bond formation. Figure 7 shows a method where metal powder is first reduced (ie, oxygen is removed). In other words, this is the opposite of oxidation. To further elaborate, after a predetermined time and temperature in a predetermined atmosphere, and predetermined mechanical, abrasive or kinetic working or electrical discharge (i.e corona) on the powders, the oxide layer is either reduced in thickness and/or the oxide layer is disrupted. If left untreated, the reduced metal powder can oxidise again readily and, to that end, the reduced metal powders are treated with the coupling agent. The coupling agent prevents further oxidation and, as noted above, promotes bonds with the polymer in manufacture of the composite structure 10. Furthermore, for storing for future use, the coupling agent and reduced metal powder may be hermetically sealed.

[00167] In a similar manner to Figure 7, Figure 8 shows a method where metal powder is reduced, and then mixed with graphene nanoparticles to assist in preventing further oxidation as well as promoting bonds with the polymer during manufacturing of the composite structure 10. In some embodiments, this may reduce the need for the coupling agent as the metallic particles can suitably bond with the polymer. In addition, after coating the metallic particles with graphene, they can be hermetically sealed for future use.

[00168] Supersonic spraying of metallic particles directly onto the surface of the fibre- reinforced polymer 20 is likely to cause damage to the polymer matrix and/or fibres making up the fibre-reinforced polymer 20. This is due to the fibre-reinforced polymer 20 not having sufficient wear/erosion resistance to withstand supersonic spray deposition of metallic particles. Further, metallic particles applied directly to the surface of the fibre-reinforced polymer 20 by supersonic particle deposition will likely not adhere strongly to it. The use of the metallised surface region 30 (or plasticised surface region in other embodiments) with fibre-reinforced polymer 20 assists in addressing these issues. In particular, the binder particles in the metallised (bonding) surface region 30 shield the fibre-reinforced polymer 20 and provide wear/erosion resistance. The metallic particles also provide substrate binding sites upon which the supersonic sprayed metallic particles can deform and adhere. This also improves the fracture mechanics of the composite structure 10, 10' along with avoiding issues of, for example, delamination.

[00169] It may be desirable to provide the metallised surface region 30 over the entire surface of the mould surface 110 and thus over the entire surface of the moulded fibre-reinforced polymer 20. However, as noted above, the metallised surface region 30 may be provided on one or more selected regions of the mould surface 110 in order to produce a structure in which the metallised surface region 30 is provided on corresponding region(s) of the fibre-reinforced polymer 20. The nature of the present invention (ie, using a mould to form the region 30) allows selected regions to be targeted which provides a number of non-obvious advantages. For example, material waste may avoided by selecting certain areas that require coatings while less critical areas are circumvented. This is advantageous compared to other techniques that may include metallic (or plastic) particles throughout the fibre-reinforced polymer 20 whilst not being necessary. In further embodiments, the metallised surface 30 region may be included on opposite sides of the fibre- reinforced polymer 20 depending on the application.

[00170] The composite structure 10, 10' may be useful in aerospace, defence, automotive, marine, windmills and construction applications. For example, in aerospace applications the process invention may be applied to produce aircraft components such as wing and tail sections, nose cones for missiles etc. In this regard, the process may be implemented for the production of large components along with smaller components. The process may also be useful for producing consumer products such as luggage. By way of example, the process may be applied to produce lightweight luggage having a coating of titanium on exterior surfaces. The titanium coating is wear/scratch-resistant as well as providing aesthetic appearance and structural improvements for products such as bicycles, surfboards, tennis rackets, hockey sticks, snow skies etc. The present invention can also be carried out on a commercial scale.

[00171] The use of supersonic particle deposition also provides flexibility in achieving certain properties. For example, copper normally has a much lower critical velocity impact in supersonic particle deposition compared to that of titanium. In further embodiments, copper may be sprayed as the first layer on to the binder layer 30 which enables forming sound well adhered coatings on the binder layer 30 followed by spraying titanium which can be sprayed at higher velocity without risk of damaging the fibre-reinforced polymer 20. The copper layer provides a suitable source for heat transfer whilst titanium provides a harder wearing layer. As noted above, the metal particles in the metallised surface region 30 also protect the fibre-reinforced polymer 20, as supersonic metal particles are deposited. This avoids (for example) a polymer or resin having to withstand these supersonic particles alone which can lead to a number of non-obvious structural issues.

[00172] In this specification, adjectives such as first and second, left and right, top and bottom, and the like may be used solely to distinguish one element or action from another element or action without necessarily requiring or implying any actual such relationship or order. Where the context permits, reference to an integer or a component or step (or the like) is not to be interpreted as being limited to only one of that integer, component, or step, but rather could be one or more of that integer, component, or step etc.

[00173] The above description of various embodiments of the present invention is provided for purposes of description to one of ordinary skill in the related art. It is not intended to be exhaustive or to limit the invention to a single disclosed embodiment. As mentioned above, numerous alternatives and variations to the present invention will be apparent to those skilled in the art of the above teaching. Accordingly, while some alternative embodiments have been discussed specifically, other embodiments will be apparent or relatively easily developed by those of ordinary skill in the art. The invention is intended to embrace all alternatives, modifications, and variations of the present invention that have been discussed herein, and other embodiments that fall within the spirit and scope of the above described invention.

[00174] In this specification, the terms ‘comprises’, ‘comprising’, ‘includes’, ‘including’, or similar terms are intended to mean a non-exclusive inclusion, such that a method, system or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed.