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Title:
MULTILAYER COATING
Document Type and Number:
WIPO Patent Application WO/2010/086598
Kind Code:
A1
Abstract:
A coating and a method of forming the same on a substrate is provided. The coating is provided with at least one ceramic material layer and at least one metal material layer. At least one of the materials used is a shape memory alloy so as to provide elasticity in the coating so as to allow any deformation of the same to be substantially recovered.

Inventors:
NICHOLLS JOHN RAYMENT (GB)
LAWSON KEN JOHN (GB)
RAO JEFF (GB)
GORRUPA ALEX (GB)
Application Number:
PCT/GB2010/000128
Publication Date:
August 05, 2010
Filing Date:
January 28, 2010
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
TEER COATINGS LTD (GB)
UNIV CRANFIELD (GB)
NICHOLLS JOHN RAYMENT (GB)
LAWSON KEN JOHN (GB)
RAO JEFF (GB)
GORRUPA ALEX (GB)
International Classes:
C23C28/00; C23C14/35
Domestic Patent References:
WO2005121038A22005-12-22
WO2007136777A22007-11-29
Foreign References:
US20040202888A12004-10-14
US20060147728A12006-07-06
EP0366289A11990-05-02
US5656364A1997-08-12
US6399219B12002-06-04
US20070158200A12007-07-12
Other References:
None
Attorney, Agent or Firm:
BAILEY WALSH & CO LLP (Leeds LS1 2SD, GB)
Download PDF:
Claims:
Claims

1. A wear resistant coating for a surface of a substrate, said coating having at least one metallic layer and at least one ceramic material layer and having sufficient elasticity to provide protection against impact, erosion and/or cyclically loaded wear processes.

2. A coating according to claim 1 wherein the said coating consists of at least four layers.

3. A coating according to claim 1 or 2 wherein the coating consists o f a plurality of metallic material and ceramic material layers .

4. A coating according to claim 3 wherein layers of ceramic alternate with layers of metallic material.

5. A coating according to claim 3 wherein at least one o f the metallic layers is formed from a 'shape memory alloy'.

6. A coating according to claim 3 wherein the ceramic layer is any, or any combination, of a boride, carbide, nitride or oxide of metals from group s 4, 5 or 6, and/or aluminium and/or silicon.

7. A coating according to claim 3 wherein there is provided a coating with an alloy layer and at least one ceramic layer formed from boride, carbide, nitride or oxide.

8. A coating according to claim 3 wherein the metallic material layer comprises an NiTi alloy and/or elements selected from nickel, titanium, chromium, aluminium, platinum, hafnium, zirconium, cobalt, copper, and/or yttrium.

9. A coating according to claim 8 wherein at least the metallic material layer provides shape memory alloy properties.

10. A coating according to claim 8 wherein at least the metallic layer exhibits super-elastic behaviour.

11. A coating according to claim 1 wherein the multi-layered coating is deposited at a temperature to aid the recrystallisation of the 'shape memory alloy' layer.

12. A coating according to claim 3 wherein the ceramic used is a boride, carbide, nitride or oxide of one of the alloying elements included in the metallic layer material.

13. A coating according to claim 12 wherein an interfacial ceramic layer is deposited that is a boride, carbide, nitride or oxide of one of the alloying elements included in the metallic layer material.

14. A coating according to any preceding claim wherein the thickness of the ceramic layer(s) lies in the range 0.1 to 5.0u_m, preferably 0.3 to 3.0 u_m.

15. A coating according to any preceding claim wherein the ceramic layer thickness is below the critical thickness of ceramic brittle fracture, defined as:

= EY,

2f.σ2

where E is the ceramic elastic modulus, Ys is the fracture surface energy for the ceramic, σ is the maximum tensile stress generated in the ceramic layers as a result of impact loading, and f is a geometric factor related to the contact geometry.

16. A coating according to claim 15 wherein the geometric factor, f, is 16 for a lqm thick ceramic layer with a modulus of 300GPa.

17. A coating according to any of the preceding claims wherein the ceramic layer is itself a multiplicity of sub-layers.

18. A coating according to claim 17 wherein said sub-layers are of different ceramic composition and the ceramic layer exhibits a super-lattice structure, which improves both its hardness and fracture resistance.

19. A coating according to any of the preceding claims wherein the first ceramic layer is bonded to the substrate material by an adhesion layer.

20. A coating according to claim 19 wherein the adhesion layer is formed of a metal or an alloy specifically chosen to aid bonding between the ceramic layer and the substrate.

21. A coating according to claim 20 wherein the adhesion layer is titanium and/or chromium or an alloy based on titanium or chromium.

22. A coating according to claim 19 wherein the adhesion layer enhances the bonding of the first ceramic layer and provides a diffusion barrier function.

23. A coating according to claim 3 wherein the shape memory alloy layer thickness is between 0.5x and 2.0x the ceramic layer thickness.

24. A coating according to claim 3 wherein the plurality of layers extends to 25 repeat metal plus ceramic bi-layers, one of which is the metallic adhesion layer.

25. A wear resistant coating of a plurality of alternating layers of metallic and ceramic materials, the metallic layers having high ductility and super-elastic properties.

26. A coating according to claim 25 wherein the metallic layer has a thickness between 0.3 and 3.0 μm.

27. A coating according to claim 25 wherein the thickness of any ceramic layer in the plurality of alternating layers never exceeding the critical defect size for ceramic brittle fracture.

28. A method of forming an elastic coating on a substrate said method including the steps of applying a plurality of layers of ceramic material and a plurality of layers of metallic material and wherein said layers of ceramic material alternate with the layers of metallic material as the coating is formed.

29. A method of forming a coating according to claim 28 wherein a sputtering process is used to form at least the ceramic layer or layers.

30. A method according to claim 29 wherein a closed field, unbalanced magnetron sputter ion plating (CFUBMSIP) method is used.

31. A method of forming a coating according to claim 28 wherein a sputtering process is used to apply at least the metallic layer.

32. A method according to claim 31 wherein a closed field unbalanced magnetron sputter ion plating (CFUBMSIP) is used.

Description:
Multilayer Coating

The present invention relates to a method o f forming a coating, and the coating itself. A problem with existing coatings is that while they can be formed to have specific properties this may be to the detriment of other characteristics of the coating and this therefore restricts the usefulness of the coating to specific purposes .

It is known from US patent numbers 4554201 , 4895770, 4904542 and 5656364 to produce multiple layered wear resistant coatings onto a substrate, where the layered systems are resistant to wear associated with metal cutting (US 4554201 and US 4895770) , sliding wear or erosion (US 4904542, US 5656364) .

It is know from both US (US 5656364) and European patents (EP0366289A, EP0289173A) to produce multiple layer wear resistant coatings on the surface o f a substrate using alternating layers of metallic material and the nitride, carbide or oxide of the metallic material. Specifically in patent EP02089173A the multiple layers consist of titanium and titanium nitride. In patent US 4904542 the multiple layers consist of either titanium, zirconium, hafnium or tantalum plus nitrides of the chosen material. In patent US 5656364 the multiple layers consist of titanium diboride and a metallic material with high elastic modulus, e.g. an alloy based on tungsten. Patent US 5656364 precludes the use of low elastic modulus materials, citing aluminium and titanium, for use in the erosion resistant multilayer coating system disclosed therein.

The aim of the present invention is to provide a coating which is elastic in characteristic in that deformation of the same is substantially recovered, whilst achieving a relatively hard wearing characteristic.

In a first aspect of the invention there is provided a wear resistant coating for a surface of a substrate, said coating having at least one metallic material layer and at least one ceramic material layer and having sufficient elasticity to provide protection against impact, erosion and/or cyclically loaded wear processes .

In one embodiment the coating consists o f a plurality of metallic material and ceramic material layers . In one embodiment the said coating consists of at least four layers . Typically the layers of ceramic alternate with the layers of metallic material.

In one embodiment at least one of the metallic layers is formed from a 'shape memory alloy' which, typically, provides the required elastic properties.

In one embodiment the ceramic layer is any, or any combination, of a boride, carbide, nitride or oxide o f metals from groups 4, 5 or 6, and/or aluminium or silicon. In accordance with one form of the invention there is provided a coating with an alloy layer and at least one ceramic layer formed from boride, carbide, nitride or oxide.

Typically, the metallic layer comprises an NiTi alloy and/or elements selected from nickel, titanium, chromium, aluminium, platinum, hafnium, zirconium, cobalt, copper, and/or yttrium to provide shape memory alloy properties, and preferably super- elastic behaviour. In one embodiment the multi-layered coating is deposited at a temperature to aid the recrystallisation of the 'shape memory alloy' layer.

Typically the ceramic used is a boride, carbide, nitride or oxide of one of the alloying elements included in the 'shape memory alloy' material to ensure good chemical bonding between the respective layers.

In one embodiment an interfacial ceramic layer is deposited. In one embodiment the said interfacial layer is a boride, carbide, nitride or oxide of one of the alloying elements included in the 'shape memory alloy' material.

Typically the thickness of the ceramic layer(s) lies in the range 0.1 to 5.0um, preferably 0.3 to 3.0 u_m.

In one embodiment the ceramic layer thickness is below the critical thickness of ceramic brittle fracture, defined as:

h, = EY.

2Lo 2

where E is the ceramic elastic modulus, Ys is the fracture surface energy for the ceramic, σ is the maximum tensile stress generated in the ceramic layers as a result of impact loading, and f is a geometric factor related to the contact geometry, typically 16 for a l u_m thick ceramic layer with a modulus of 300GPa.

In one embodiment the ceramic layer is itself a multiplicity of layers and each layer may be of different ceramic composition whereby the ceramic layer exhibits a super-lattice structure, which improves both its hardness and fracture resistance. In a further aspect of the invention there is provided a method of forming an elastic coating on a substrate, said method including the steps of applying a plurality of layers of ceramic material and a plurality of layers of metallic material and wherein said layers of ceramic material alternate with the layers of metal material as the coating is formed.

In one embodiment at least one of the metal layers is formed from a shape memory alloy.

In one embodiment a sputtering process is used to supply the ceramic layer and preferably a closed field, unbalanced magnetron sputter ion plating (CFUBMSIP) is used, to improve the adhesion and structure/habit of the ceramic layer.

In one embodiment a sputter process is used to apply the metallic layer and preferably a closed field unbalanced magnetron sputter ion plating (CFUBMSIP) is used to improve the structure/habit of the metal layer.

In one embodiment the first ceramic layer is bonded to the substrate material by an adhesion layer that is not a 'shape memory alloy' but a metal or an alloy specifically chosen to aid bonding between the ceramic layer and the substrate. In one embodiment the adhesion layer is titanium and/or chromium or an alloy based on titanium or chromium.

Typically, the first metallic layer is designed to be an adhesion layer to enhance the bonding of the first ceramic layer, which, in turn, provides a diffusion barrier function.

Typically the shape memory alloy layer thickness is between 0.5x and 2.Ox the ceramic layer thickness. In one embodiment the plurality of layers extends to 25 repeat metal plus ceramic bi-layers, one of which is the metallic adhesion layer.

In accordance with one embodiment o f the invention a wear resistant coating is formed of a plurality of alternating layers of metallic and ceramic materials. The two materials are typically selected to provide complimentary properties to the wear resistant coatings; one being hard but relatively brittle and the second having high ductility, plus super-elastic properties . The ductile super-elastic alloy is of the class of materials known as a 'Shape memory alloy'. The preferred layer thickness should lie between 0.3 and 3.0 μm, with the ceramic thickness o f any layer in the plurality of alternating layers never exceeding the critical defect size for ceramic brittle fracture.

A specific embodiment of the invention is now described with reference to the accompanying drawings; wherein

Figure 1 illustrates a plan schematic view of apparatus which can be used; and

Figure 2 illustrates one set of test results o f a coating formed in accordance with the invention.

There is provided a wear resistant coating system for a substrate in accordance with the invention which is particularly useful where the coating is subject to dynamic, reciprocating, loading and/or rolling cycles. The elasticity o f the coating means that any impact on the coating such as by an object propelled onto the coating or passing along the same and which causes deformation o f the same can be absorbed, as the elasticity of the coating ensures that once the impacting article has been removed, at least some, and preferably all, of the deformation which has been caused, is recovered.

In one embodiment the impact loading cycles may result from multiple ballistic impact which, in conventional surfaces or coatings, cause an erosion effect introduced by particles impacting the coating substrate system. However in the coating created in the current invention, there is provided a multilayer erosion resistant coating system. In one embodiment the coatings can be used for gas turbine engine and/or steam turbine components, e.g compressor blades within gas turbines and turbine blades in steam turbines where the adverse affects of impact loads are typically experienced. A second field with similar cyclic loads is a the rolling contact fatigue experienced in all bearing systems for highly loaded mechanical machines including automotive, aerospace, wind turbines and manufacturing applications.

A second field with similar loading cycles is the rolling contact fatigue experienced in all bearing systems, for highly loaded mechanical machines including automotive, aerospace, various manufacturing applications, power generation, precision machining and industrial manufacturing processes . Figure 2 illustrates test results obtained from repeat wear tests over a number of cycles and at loads of 30 Newtons, 40 Newtons and 50 Newtons and in which the results for the friction co-efficient values show that the coating is resistant to fatigue streams and protects against rolling contact fatigue as the friction coefficient value remain substantially consistent as the number of cycles increases .

A third field is resistance- to three body abrasion associated with pumping particle loaded fluids in the oil and gas industry, offshore power sectors, mining and mineral processing industries.

The possible applications of the coating in accordance with the present invention are not limited to those cited above. The coating can provide improved durability and functionality under any reciprocating loaded wear event.

Referring now to Figure 1 , there is illustrated apparatus which can be used to form a coating in accordance with the invention.

The apparatus is provided as a closed field unbalanced magnetron sputter ion plating apparatus in which there is provided a chamber 2 in which a vacuum can be created and a holder 4 which is provided to be rotatable about axis 6. On the external, side walls 8 of the holder, there are provided the substrates to be coated as the holder is rotated. Facing towards said substrates, at the periphery of the chamber, are provided a plurality of magnetrons 10 which can be provided in a configuration so as to form a closed field such that, for example, the magnetic configuration of adjacent magnetrons is such that the magnetic polarity o f one magnetron is the reverse to that of adjacent magnetrons so as to create a magnetic field 12 within the chamber which encourages the material sputtered from the magnetron targets, to be deposited towards the substrates to be coated on the holder 4. Alternatively, or in addition, magnet arrays can be inserted between adjacent magnetrons so as to provide the required magnetic field configuration.

The targets of the magnetrons can be provided of the required material to form the coatings on the substrates. Typically the magnetrons are operated in a predesignated sequence so as to deposit the required material at the required time so as to form the multilayered coating as desired. Furthermore, appropriate gas or gases can be introduced into the chamber during the coating process, and during the application o f particular materials so as to form the coating material to be applied.

In accordance with the invention, at least one of the magnetron having a metal target is first operated, so as to deposit the metal layer onto the substrate surface. Thereafter, at least one further magnetron is operated and gas introduced so as to deposit a ceramic material layer onto the metal layer, followed by a metal alloy layer and so on until the final coating is formed of the plurality of metal and ceramic layers.

The use of a 'Shape Memory Alloy (SMA) ' material as part of the multilayer coating system, utilises the super-elastic properties of the 'shape memory alloy' to provide additional resistance to dynamic, reciprocating, loads as might be observed during ballistic impact, erosion or cyclic fatigue loadings .

Thus, the current invention permits the accepted wear resistance of multilayered coatings to be enhanced under dynamic impact conditions through the incorporation of 'shape memory alloy' metallic layers which provide super-elastic properties to the multilayer system.