Article and a method of making an article

Abstract

An article, at least a surface of the article being made of or containing an organic material, and a thermally sprayed layer of coating material on the surface.

Claims

1. An article, the article including a surface being made of a composite material including a matrix made of plastics material or a surface being made of an organic material, and a thermal sprayed first layer of coating material directly on the surface, and a further layer directly on the first layer, the coating material of the first layer being wholly metal material, the first layer being less than 200 micrometres in thickness and the further layer being of a material with a higher melting point than the coating material of the first layer and comprises at least 50 wt. % zirconia, titania or alumina, wherein the first layer is electrically conductive and may be connected to earth to provide electromagnetic shielding, and wherein the article is provided by a method in which the first layer is bonded to the surface with only micro-scale melting of the surface by thermally spraying at a rate of less than 70 g/min, and in which the further layer is bonded to the first layer with only micro-scale melting of the surface by thermally spraying particles of size 50 to 90 micrometres at a rate of less than 100 g/min.

2. An article according to claim 1, wherein the surface is made of carbon fibre composite material.

3. An article according to claim 1, wherein the first layer is up to 150 micrometres in thickness.

4. An article according to claim 1, wherein the first layer is up to 100 micrometres in thickness.

5. An article according to claim 1, wherein the further layer is a thermally sprayed layer, and has a level of porosity of greater than 15%.

6. An article according to claim 1, wherein the further layer is wholly or principally made of ceramic material.

7. An article according to claim 1, wherein the further layer comprises at least 50% of zirconia.

8. An article, the article including a surface being made of a composite material including a matrix made of plastics material or a surface being made of an organic material, and a thermal sprayed first layer of coating material directly on the surface, and a further layer directly on the first layer, the coating material of the first layer being wholly metal material, the further layer comprising at least 50 wt. % of zirconia, wherein the first layer is electrically conductive and may be connected to earth to provide electromagnetic shielding, and wherein the article is provided by a method in which the first layer is applied to the surface with only micro-scale melting of the surface by thermally spraying at a rate of less than 70 g/min, and in which the further layer is bonded to the first layer with only micro-scale melting of the surface by thermally spraying particles of size 50 to 90 micrometres at a rate of less than 100 g/min.

9. An article according to claim 1, wherein, the further layer comprises wholly or principally zirconia.

10. An article as claimed in claim 1, wherein the further layer is at least as thick as the first layer.

11. An article as claimed in claim 1, wherein the further layer is thicker than the first layer.

12. An article as claimed in claim 1, wherein the further layer is at least 100 micrometres thick.

13. An article as claimed in claim 1, wherein the further layer is at least 150 micrometres thick.

14. An article as claimed in claim 1, wherein the further layer is not greater than 300 micrometres thick.

15. An article as claimed in claim 8, wherein the further layer is not greater than 250 micrometres thick.

16. A method of coating a surface being made of a composite material including a matrix made of plastics material or a surface being made of an organic material, the method comprising thermal spraying a first layer of coating material directly onto the surface and to a thickness of less than 200 micrometres, and thus bonding the first layer of coating material to the surface with only micro-scale melting of the surface by thermally spraying at a rate of less than 70 g/min, and subsequently depositing a further layer directly on the first layer, the further layer being bonded to the first layer with only micro-scale melting of the surface by thermally spraying particles of size 50 to 90 micrometres at a rate of less than 100 g/min, the coating material of the first layer being wholly metal material, the further layer being of a material with a higher melting point than the coating material of the first layer, wherein the first layer is electrically conductive and may be connected to earth to provide electromagnetic shielding.

17. A method according to claim 16, wherein the first layer of coating material is plasma sprayed onto the surface.

18. A method according to claim 16, wherein the first layer up to 150 micrometres in thickness.

19. A method according to claim 16, wherein the first layer is up to 100 micrometres in thickness.

20. A method according to claim 16, wherein the further layer is deposited by plasma spraying.

21. A method according to claim 16, wherein the further layer is wholly or principally made of ceramic or metal or ceramic and metal.

22. A method according to claim 16, wherein the further layer is wholly or principally made of ceramic.

23. A method according to claim 21, wherein the further layer comprises at least 50 wt. % of zirconia.

24. A method as claimed in claim 23, wherein the further layer comprises wholly or principally zirconia.

25. A method according to claim 16, wherein the further layer is deposited to be at least as thick as the first layer.

26. A method according to claim 16, wherein the further layer is deposited to be thicker than the first layer.

27. A method according to claim 16, wherein the further layer is deposited to be at least 100 micrometres thick.

28. A method according to claim 16, wherein the further layer is deposited to be at least 150 micrometres thick.

29. A method according to claim 16, wherein the further layer is deposited to be not greater than 300 micrometres thick.

30. A method according to claim 16, wherein the further layer is deposited to be not greater than 250 micrometres thick.

31. An article according to claim 1, wherein the article is non-cylindrical.

32. An article according to claim 1, wherein the first layer is wider than the further layer.

33. An article according to claim 8, wherein the article is non-cylindrical.

34. An article according to claim 8, wherein the first layer is connected to an earth surface to provide electromagnetic shielding.

35. An article according to claim 8, wherein the first layer is wider than the further layer.

36. A method according to claim 16, wherein the article is non-cylindrical.

37. A method according to claim 16, wherein the surface is mounted on a coupon for spraying, and the coupon is static during spraying of the first layer and further layer.

38. A method according to claim 16, wherein the first layer is wider than the further layer.

39. An article according to claim 1, wherein the article has a complex geometry.

40. An article according to claim 8, wherein the article has a complex geometry.

41. An article according to claim 16, wherein the article has a complex geometry.

42. A method according to claim 16, wherein the surface is mounted on a rotating turntable for spraying.

43. A method according to claim 16, wherein the first layer of coating material is thermal sprayed by hand spraying.

44. A method according to claim 43, wherein the surface is of a complex shape.

45. A method according to claim 16, wherein the further layer is thermal sprayed by hand spraying.

46. A method according to claim 45, wherein the surface is of a complex shape.

47. An article according to claim 8, wherein the further layer is a thermal barrier layer.

48. An article according to claim 1, wherein the further layer is a thermal barrier layer.

49. An automobile part comprising a surface coated according to the method of claim 16.

Description

(1) Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a side elevation in cross section of a coupon in a first embodiment of the invention;

(3) FIG. 2 is a fragmentary detail perspective view partly in cross section of a part in a second embodiment of the invention;

(4) FIG. 3 shows a golf club according to Embodiment 6 of the present invention;

(5) FIG. 4 shows the head of the golf club of FIG. 3, in fragmentary detail;

(6) FIG. 5 shows a bicycle wheel according to Embodiment 7 of the present invention; and

(7) FIG. 6 shows a hip prosthesis according to Embodiment 8 of the present invention.

EMBODIMENT 1

(8) A coupon 10 of carbon fibre reinforced plastics material of dimensions 150 mm×150 mm by 2 mm thick was carefully cleaned, using acetone, then wiped with tissue to remove any liquid. The clean coupon 10 was then grit blasted on one side using a siphon type grit blast system at 40 psi, with grit of between 0.4 and 0.6 mm size. The coupon 10 was blown with dry air to remove any debris and wiped with an acetone damp tissue.

(9) The coupon 10 was then mounted onto a turntable in a plasma spray booth, containing a robot manipulation system. The spray system was set to work in nitrogen and aluminium powder feed set to spray at 30 gm/min. Nitrogen flow was preset to 50 litres/min. and current to 300 Amps. The robot was programmed to operate a ladder type spray pattern, at a stand off distance of 100 mm from the coupon, while the coupon 10 was rotated. In this way, an aluminium bond coat of approximately 25 μm thickness was applied. A second coat was then applied in the same way to provide a layer 12 with a total coating thickness of 50 μm.

(10) Careful choice of the spray parameters ensures that the bond coat 12 “welds” itself to the surface of the coupon 10 with only micro-scale melting of the surface. It is key to control the amount of heat that is transferred via the metal spray to the coupon surface, thus minimising any localised damage to the carbon fibre reinforced plastics material.

(11) Using the same type of spray program at 75 mm spray distance, using standard nitrogen plasma parameters, magnesium zirconate was plasma sprayed onto the aluminium coating on the coupon at 44 gm/min. Five coats gave a layer 14 with a thickness of 200 μm.

(12) Repeating the aluminium spray program, but only applying one coat on top of the magnesium zirconate coating, gave a thin 25 μm metal layer 16. This was rubbed down using fine emery paper to give a smooth, shiny surface 18.

(13) Carbon fibre reinforced plastics material is naturally relatively soft and susceptible to abrasion. The use of an aluminium bond layer 12 in this example allows a layer 14 of ceramic in the form of magnesium zirconate to be applied. This has good resistance to abrasion and other mechanical damage and is very hard. It is also resistant to corrosion or chemical attack and has very good thermal resistance forming a thermal barrier to protect the carbon fibre reinforced plastic material 10. It will be understood that it is the plastics matrix of the composite that is particularly vulnerable. Its protection by the ceramic layer 14 enables the use of carbon fibre composite material in environments which heretofore have been too harsh. The top layer of aluminium 16 gives an attractive finish to the visible surface 18, as well as providing further protection.

(14) The resulting article 20 is very light in relation to its strength, certainly lighter than an equivalent in steel. An article 20 made in this way may be used for example as an automotive heat shield for extreme temperature conditions or as an aircraft tail cone.

(15) If the aluminium layer 12 is connected to earth it provides electromagnetic shielding.

(16) Instead of rubbing down the top layer 16 of aluminium with abrasive paper to achieve a smooth, shiny surface, the surface could be abraded for example by grit blasting or shot peening. Alternatively, the surface could be flamed to virtually melt, which results in a highly reflective surface finish.

EMBODIMENT 2

(17) In this embodiment, a carbon fibre reinforced plastics part 30 is prepared for use as a heat shield. The intended environment requires higher temperature operation than normal for a carbon fibre reinforced plastics part. A carbon fibre reinforced plastics substrate 32 was pre-prepared in the same way as in embodiment 1, except that in this embodiment, the whole area of the surface of the substrate 32 is not being treated, only a selected area. Thus, areas 34 at the sides of the surface which do not require coating were masked with propriety masking tape to leave an unmasked central area.

(18) In a plasma spray booth equipped for hand spraying, a copper bond coat 36 of 50 μm thickness was applied using an oxy-acetylene wire spray system, using the following parameters: oxygen=23 slpm, acetylene=18 slpm, feed rate of 25 g/min and a spray distance of 150 mm.

(19) A further mask was then applied to side areas of the copper bond coat 36. A trained operator, using a hand held plasma torch, and parameters as follows: nitrogen=45 slpm, hydrogen=5 slpm, feed rate of 50 g/min, current=500 Amps, sprayed a layer 38 of magnesium zirconate onto the unmasked area of the bond coat 36, to give a creamy white ceramic layer 38 with a thickness of 300 μm.

(20) The part 30 is intended for use in an engine bay of a vehicle with an internal combustion engine. The part 30 will be situated near a hot rod 40 as shown in FIG. 2. The part is thus arranged so that the ceramic layer 38 is directly below the hot rod 40.

(21) In use, as the rod 40 heats up, the ceramic layer 38 will act as a heat barrier to protect the carbon fibre reinforced plastics substrate 32. The copper layer 36, as well as acting as a bond layer to adhere the ceramic to the carbon fibre reinforced plastics substrate 32, also acts as a heat sink to conduct heat away and to dissipate heat. The uncoated parts 34 of the carbon fibre reinforced plastics substrate 32 are so far away from the rod 40 that the heat from the rod will not degrade them.

(22) The fact that the layers are only applied where they are needed avoids unnecessary weight gain, which is important in a vehicle, as well as in other contexts.

(23) The masking here is in strips and so is straightforward, but more complex masking can be used where required. In another embodiment, the masking may be used to enable a pattern or words to be sprayed onto a ceramic surface in a polishable metal for example to represent and display a trade mark. It is also possible to build up the surface coating by further metal spraying or by deposition in other ways to fabricate three dimensional features on the surface of the substrate. These might provide attachment or load bearing points or other features. In this case, the underlying metallic coat may be used to provide a degree of strengthening and load spreading. The use of an intermediate ceramic layer will protect the carbon composite material from conductive heat transfer via these features.

(24) It is preferred to spray by robot, due to reproducibility, though where a component is of a complex shape, it may be more appropriate to use hand spraying.

EMBODIMENT 3

(25) A carbon fibre reinforced plastics material part to form a car bonnet was carefully cleaned, using acetone, then wiped with tissue to remove any liquid. The clean part was then grit blasted on one side using a siphon type grit blast system at 40 psi, with grit of between 0.4 and 0.6 mm size. The part was blown with dry air to remove any debris.

(26) The part was then mounted in a plasma spray booth, containing a robot manipulation system. The spray system was set to work in nitrogen and aluminium powder feed set to spray at 30 gm/min. Nitrogen flow was preset to 50 litres/min. and current to 300 Amps. The robot was programmed to operate a ladder type spray pattern, at a stand off distance of 100 mm from the part. In this way, an aluminium bond coat of approximately 25 μm thickness was applied. A second coat was then applied in the same way to provide a total coating thickness of 50 μm.

(27) Gold was then deposited onto the part by wire-spray processing onto the aluminium coating on the part. A thickness of 150 μm was achieved. The surface was then chemically etched to achieve the desired finish.

(28) The gold layer will conduct and dissipate heat. A gold foil lining tacked to the inside of an engine bay is known, but the layer of the present invention is firmly adhered to the carbon fibre composite part.

(29) Although surface roughening has been described, some substrates may be sufficiently rough in their basic state not to require further roughening.

(30) The invention provides a coating on a carbon fibre composite material which is very firmly adhered and by appropriate choice of top layers can provide a wide range of physical properties as desired.

EMBODIMENT 4

(31) A carbon fibre reinforced plastic brake shield had a layer of aluminium foil bonded to the surface during the manufacturing process. Using appropriate protective clothing, the surface was treated with 3M NaOH solution and left for fifteen minutes. The surface was then water washed to remove any solution and debris and allowed to dry. The surface was roughened by grit blasting on one side using a siphon type grit blast system at 40 psi, with grit of between 0.4 and 0.6 mm size. The surface was then blown with dry air to remove any debris and wiped with an acetone damp tissue. Magnesium zirconate ceramic was then applied in the same manner as in Embodiment 2.

EMBODIMENT 5

(32) A carbon fibre reinforced plastic heat shield, coated with magnesium zirconate ceramic, was subject to impact damage during routine maintenance.

(33) A 50 μm layer of molybdenum was applied using a Metco™ 9 MB plasma spray gun, mounted on a Staubli™ robot, using the following parameters: Powder feed rate—25 g/min Nitrogen flow—80 scfh Hydrogen flow—10 scfh Current—500 A Spray distance—100 mm Traverse rate—150 mm/s

(34) The surface integrity of the ceramic was enhanced by the addition of this thin molybdenum coating, so that if any damage was done to the ceramic, the metal layer would held it together, preventing spalling.

(35) An alternative application for this invention is applying coatings to polymeric materials and carbon fibre reinforced polymeric materials for medical and/or orthopaedic implants in cases where surface coatings (such as hydroxyapatite coatings) are required to promote bone in-growth and enhance the fixation of implants.

EMBODIMENT 6

(36) A golf club 50, as shown in FIGS. 3 and 4, with a carbon fibre reinforced plastic golf club head 52 was coated with magnesium zirconate ceramic on the striking face 54 of the head 52 and the bottom 56 of the head 52 in the same way as in Embodiment 2. To avoid impact damage, a 50 μm molybdenum layer was applied to the magnesium zirconate layer, in the same manner as described in Embodiment 5. As in Embodiment 5, if damage was done to the ceramic, the metal layer held it together, preventing spalling.

EMBODIMENT 7

(37) A carbon fibre reinforced plastic bicycle wheel 60, as shown in FIG. 5, quickly suffered wear when brakes pads were applied to the rim 62.

(38) A bond coat comprising aluminium was plasma sprayed onto the braking area 64 of the rim 62 of the wheel 60, namely the area of the rim to be contacted by a brake block in use. The bond coat was deposited to a thickness of ˜100 μm. The plasma spray parameters used were nitrogen 50 slpm, hydrogen 5 slpm, current 400 Amps, carrier gas 5 slpm, spray distance 100 mm, powder flow 45 g/min.

(39) A 100 wt. % titanium dioxide ceramic layer was then applied on top of the bond coat by plasma spraying. The ceramic layer was applied to a thickness of ˜200 μm. The plasma spray parameters used were Nitrogen 45 slpm, hydrogen 5 slpm, current 500 Amps, carrier gas 5 slpm, spray distance 75 mm, powder flow 65 g/min, ceramic powder particle size 50 to 90 micrometres.

(40) The wear resistance of the wheel rim 62 was increased by the coatings.

EMBODIMENT 8

(41) A carbon fibre reinforced plastic hip prosthesis 70, comprising a stem 72 and a ball 74, as shown in FIG. 6, was plasma sprayed with a 50 μm silver layer and then a 150 μm titanium layer. A 150 μm hydroxyapatite layer was then plasma sprayed onto the on the surface of the stem 72. The hydroxyapatite coating helped to promote bone ingrowth and enhance the fixation of the implant to the femur.