GB2439389A

GB2439389A - Multi layer coatings

Info

Publication number: GB2439389A
Application number: GB0612357A
Authority: GB
Inventors: Jorg Peter Feist; John Raymond Nicholls; Michael James Fraser; Andrew Lawrence Heyes
Original assignee: Southside Thermal Sciences STS Ltd
Current assignee: Southside Thermal Sciences STS Ltd
Priority date: 2006-06-22
Filing date: 2006-06-22
Publication date: 2007-12-27
Also published as: GB0612357D0

Abstract

A thermal barrier coating 3 comprising a plurality of layers 3a-3d. Adjacent layers are formed of different host materials preferably having different crystal and/or chemical structures. At least one of the layers 3d includes a luminescent material and is thus luminescent. Host materials disclosed include zirconia e.g. YSZ, aluminium containing oxides e.g. YAG, YAP and pyrochlores. The luminescent dopant can be terbium, praseodymium or other lanthanides and can be distributed as discrete particles throughout the host material. The presence of luminescent material within the coating allows in situ measurement of some of the coatings properties. Interfacial layers may also be provided 3b, 3c.

Description

MULTI-LAYER COATINGS

The present invention relates to coatings, such as thermal barrier coatings (TBC5), which incorporate luminescent materials, and which are in particular for use in high-temperature environments.

TBCs are structural coatings which are applied to components which are subjected to high temperatures, often greater than 1000 C, and thus would be prone to oxidation and corrosion processes. Typical applications are in the aviation and power generation industries, particularly in the coating of turbine components, such as turbine blades.

Existing TBCs are predominantly formed from yttria-stabilized zirconia (YSZ), though other ceramic materials, such as yttrium aluminium garnet (YAG) and pyrochiores, are now being considered.

As disclosed in the applicant's earlier WO-A-00/06796, the provision of luminescent materials in TBCs enables the in situ optical measurement of characteristics, in particular the temperature, of the TBCs.

The ability optically to measure in situ characteristics of TBCs is of great advantage, but the existing TBCs where incorporating luminescent materials suffer from a number of disadvantages.

Existing TBCs which utilize YSZ as the host material are unable to operate at higher temperatures, typically those in excess of 900 C, as the luminescence is not sufficient to enable measurement.

Other existing TBC5 which utilize other host materials, such as YAG and pyrochlores, are operative at higher temperatures, but these materials have material properties which are not particularly suited to use as thermal barrier coatings. In particular, these materials have higher thermal conductivities, less suitable crystal structures and thermal expansion coefficients, and inferior shock and erosion resistances.

The present inventors have recognized that it is possible to provide multi-layer coatings, in particular as TBCs, which incorporate luminescent materials, and which are in particular operative in high-temperature environments, typically in excess of 1000 C. The state of the art, for example, as represented by US-A-4774150, does disclose multi-layered TBCs, where the respective layers incorporate different dopants, but, in these TBCs, the layers are formed of the same host material.

There is no recognition of forming the layers from different host materials, which enables in particular the provision of multi-function coatings.

In one aspect the present invention provides a coating comprising a plurality of layers, wherein each of the adjacent ones of the layers are formed of different host materials, and preferably one or both of different crystal and chemical structures, and at least one of the layers comprises a luminescent layer which includes a luminescent material.

Preferred embodiments of the present invention will now be described hereinbelow by way of example only with reference to the accompanying drawings, in which: Figure 1 schematically represents a TBC as applied to an object in accordance with a first embodiment of the present invention; Figure 2 schematically represents a TBC as applied to an object in accordance with a second embodiment of the present invention; and Figure 3 schematically represents a TBC as applied to an object in accordance with a third embodiment of the present invention.

Figure 1 illustrates a coating 3, in this embodiment a TBC, in accordance with a first embodiment of the present invention as applied to an object 5, which is to be subjected to high-temperature environments, typically temperatures in excess of 1000 C. The coating 3 comprises a plurality of layers, in this embodiment first, second, third and fourth layers 3a, 3b, 3c, 3d, with each of the adjacent ones of the layers 3a, 3b, 3c, 3d being formed of different structural materials, in one embodiment of one or both of different crystal and chemical structures.

In this embodiment the lowermost, first layer 3a is provided as a thermal barrier layer of low thermal conductivity, the uppermost, fourth layer 3d is provided as a luminescent layer, which inter a/ia enables characterization of the temperature of the high-temperature, ambient atmosphere, and at least the third layer 3c, and in this embodiment the second and third layers 3b, 3c, act inter a/ia as interfacial layers between the lowermost and uppermost layers 3a, 3d.

This configuration enables the otherwise-incompatible luminescent layer 3d to be incorporated in the coating 3 without altering the functionality of the coating 3, that is, at least in terms of the thermally-protective effect of the thermal barrier layer 3a.

Figure 2 illustrates a coating 13, in this embodiment a TBC, in accordance with a second embodiment of the present invention as applied to an object 15, which is to be subjected to high-temperature environments, typically temperatures in excess of 1000 C. The coating 13 comprises a plurality of layers, in this embodiment first, second, third and fourth layers 13a, 13b, 13c, 13d, with each of the adjacent ones of the layers 13a, 13b, 13c, 13d being formed of different structural materials, in one embodiment of one or both of different crystal and chemical structures.

In this embodiment the lowermost, first layer 13a is provided as a thermal barrier layer of low thermal conductivity, the third layer 13c is provided as a luminescent layer, the second layer 13b acts as an interfacial layer between the thermal barrier and luminescent layers 13a, 13c, and the fourth layer 13d is provided as a protective layer which provides at least one or both of physical or chemical protection to the underlying luminescent layer 13c.

This configuration enables the otherwise-incompatible luminescent layer 13c to be incorporated in the coating 13 without altering the functionality of the coating 13, that is, at least in terms of the thermally-protective effect of the thermal barrier layer 13a.

Figure 3 illustrates a coating 23, in this embodiment a TBC, in accordance with a third embodiment of the present invention as applied to an object 25, which is to be subjected to high-temperature environments, typically temperatures in excess of 1000 C. The coating 23 comprises a plurality of layers, in this embodiment first, second and third layers 23a, 23b, 23c, with each of the adjacent ones of the layers 23a, 23b, 23c being formed of different structural materials, in one embodiment of one or both of different crystal and chemical structures.

In this embodiment the lowermost, first layer 23a is provided as a luminescent layer, the uppermost, third layer 23c is provided as a thermal barrier layer of low thermal conductivity, and the second layer 23b acts as an interfacial layer between the luminescent and thermal barrier layers 23a, 23c.

This configuration enables the otherwise-incompatible luminescent layer 23a to be incorporated in the coating 23 without altering the functionality of the coating 23, that is, at least in terms of the thermally-protective effect of the thermal barrier layer 23c.

In one embodiment the structural, host material of one or more non-adjacent ones of the layers 3a, 3b, 3c, 3d; 13a, 13b, 13c, 13d; 23a, 23b, 23c comprises a pyrochiore.

In one embodiment the structural, host material of one or more non-adjacent ones of the layers 3a, 3b, 3c, 3d; 13a, 13b, 13c, 13d; 23a, 23b, 23c comprises a zirconia-based phase.

In one embodiment the zirconia-based phase comprises zirconia -4 mol% yttria, which is a t' structure, or zirconia -8 mol% yttria, which is a cubic structure.

In one embodiment the structural, host material of one or more non-adjacent ones of the layers 3a, 3b, 3c, 3d; 13a, 13b, 13c, 13d; 23a, 23b, 23c comprises an aluminium-containing oxide.

In one embodiment the aluminium-containing oxide comprises a phase based on YAG (Y3AlFe5..O12).

In another embodiment the aluminium-containing oxide comprises a phase based on YAP (YAIO3).

In one embodiment the luminescent layer 3d; 13c; 23a comprises a pyrochlore host phase which is doped with at least one luminescent dopant.

Preferably, the at least one luminescent dopant comprises at least one of Pr and Tb.

Preferably, the host phase is doped with between 1 mol% and 10 mol% of the at least one luminescent dopant.

More preferably, the host phase is doped with between 1 mol% and 7 mol% of the at least one luminescent dopant, and in one embodiment between 3 mol% and 7 mol% of the at least one luminescent dopant.

Still more preferably, the host phase is doped with between 4 mol% and 6 mol% of the at least one luminescent dopant.

In a preferred embodiment the host phase is doped with about 5 mol% of the at least one luminescent dopant.

In another embodiment the luminescent layer 3d; 13c; 23a comprises a zirconia-based host phase and at least one luminescent dopant.

In one embodiment the zirconia-based host phase comprises YSZ, and preferably zirconia -4 mol% yttria, which is a t' structure, or zirconia -8 mol%, which is a cubic structure.

In another embodiment the zirconia-based host phase comprises a lanthanide-doped zirconia.

In one embodiment the lanthanide dopant comprises a single dopant selected from Dy, Er, Eu, Gd, Nd, Sm and Yb.

In another embodiment the lanthanide dopant comprises a pair of dopants selected from Gd and Er, Gd and Nd, Gd and Yb, Yb and Nd and Yb and Sm.

In a further embodiment the zirconia-based host phase comprises a zirconate pyrochlore.

In one embodiment the luminescent layer 3d; 13c; 23a comprises a main, host phase, and a plurality of small discrete, luminescent particles which are distributed, in this embodiment substantially uniformly, within the host phase and act, when excited by a excitation signal, to emit a luminescence signal which is representative of one or more environmental characteristics, such as temperature.

The luminescent particles are formed of a material composition which comprises a host which is doped with at least one luminescent dopant, which material composition provides a luminescent signal when excited with an excitation signal.

In one embodiment the luminescent particles comprise an A2B207 (pyrochlore) host which is doped with at least one luminescent dopant selected from Pr and Tb, where A comprises one or more elements from the lanthanide series (rare earth metals) or the actinide or series and B comprises one or more elements from the group of transition metals.

In one embodiment the at least one luminescent dopant comprises Tb.

In another embodiment the at least one luminescent dopant comprises Pr.

In a further embodiment the at least one luminescent dopant comprises Pr and Tb in combination.

Preferably, the host is doped with between 1 mol% and 10 mol% of the at least one luminescent dopant.

More preferably, the host is doped with between 1 mol% and 7 mol% of the at least one luminescent dopant, and in one embodiment between 3 mol% and 7 mol% of the at least one luminescent dopant.

Still more preferably, the host is doped with between 4 mol% and 6 mol% of the at least one luminescent dopant.

In a preferred embodiment the host is doped with about 5 mol% of the at least one luminescent dopant.

In a further embodiment the luminescent particles comprise a first, zirconia-based host phase, a second discrete phase, and at least one luminescent dopant.

In one embodiment the zirconia-based host phase comprises YSZ, and preferably zirconia -4 mol% yttria, which is a t' structure, or zirconia -8 mot% yttria, which is a cubic structure.

In a further embodiment the zirconia-based host phase comprises a zirconate pyrochlore (A2Zr2O7), where A is preferably one or more elements selected from the lanthanide group, and preferably one or more of the elements Gd, La, Nd and Sm.

Preferably, the second phase contains Y and Al.

In one embodiment the second phase includes yttria and an aluminate.

In another embodiment the second phase is a phase based on YAG (Y3AlFe5..O12).

In a further embodiment the second phase is a phase based on YAP (YAIO3).

In one embodiment the second phase is a phase which is chemically and physically stable at high temperatures of typically up to about 1700 C, and preferably when thermally cycled.

In one embodiment the at least one luminescent dopant comprises one or more elements from the lanthanide series (rare earth metals), and more preferably one or more elements selected from Dy, Tb, Eu, Gd, Tm and Sm.

In a still further embodiment the luminescent particles comprise yttria which is doped with at least one luminescent dopant.

In a yet further embodiment the luminescent particles comprise a phase based on YAG (Y3AlFe5.O12), in one embodiment YAG, which is doped with at least one luminescent dopant.

In one embodiment the at least one luminescent dopant comprises ohe or more elements from the lanthanide series (rare earth metals), and more preferably one or more elements selected from Dy, Tb, Eu, Gd, Tm and Sm.

In a yet still further embodiment the luminescent particles comprise a phase based on YAP (YAIO3), in one embodiment YAP, which is doped with at least one luminescent dopant.

The luminescent particles are small particles which are able to co-exist in the structural phase, in particular at high temperatures exceeding 1000 C. The size and distribution of the luminescent particles *is such as not significantly to alter the physical or chemical characteristics, in particular the thermal conductivity, of the main, structural host phase of the luminescent layer 23a, but yet sufficient to provide a luminescence signal.

-10 -S Preferably, the luminescent particles are of a size between about 1 nm and about 5 pm, and more preferably between about 1 nm and about 2 pm.

Still more preferably, the luminescent particles are of a size between about 1 nm and about 1 pm, preferably between about 1 nm and about 100 nm, and more preferably between about 1 nm and about 10 nm.

Preferably, the luminescent layer 23a contains between 0.1 wt% and 10 wt% of the luminescent particles.

More preferably, the luminescent layer 23a contains between 0.1 Wt% and 5 wt% of the luminescent particles, and in one embodiment between 0.1 wt% and 2 Wt% of the luminescent particles.

Still more preferably, the luminescent layer 23a contains between 0.1 wt% and 1 wt% of the luminescent particles.

Finally, it will be understood that the present invention has been described in its preferred embodiments and can be modified in many different ways without departing from the scope of the invention as defined by the appended claims.

Claims

-11 -

CLAIMS

1. A coating comprising a plurality of layers, wherein each of the adjacent ones of the layers are formed of different host materials, and preferably one or both of different crystal and chemical structures, and at least one of the layers comprises a luminescent layer which includes a luminescent material.

2. The coating of claim 1, comprising first, second, third and fourth layers, wherein the first, lowermost layer is provided as a thermal barrier layer of low thermal conductivity, the fourth, uppermost layer is provided as a luminescent layer, and at least the third layer is provided as an interfacial layer.

3. The coating of claim 2, wherein the second and third layers are provided as interfacial layers between the first and fourth layers.

4. The coating of claim 1, comprising first, second, third and fourth layers, wherein the first, lowermost layer is provided as a thermal barrier layer of low thermal conductivity, the third layer is provided as a luminescent layer, the second layer is provided as an inter-facial layer between the first and third layers, and the fourth layer is provided as a protective layer which provides at least one or both of physical or chemical protection to the third layer.

5. The coating of claim 1, comprising first, second and third layers, wherein the first, lowermost layer is provided as a luminescent layer, the third, uppermost layer is provided as a thermal barrier layer of low thermal conductivity, and the second layer is provided as an interfacial layer between the first and third layers.

6. The coating of any of claims 1 to 5, wherein the host material of one or more non-adjacent ones of the layers comprises a pyrochlore.

-12 - 7. The coating of any of claims 1 to 5, wherein the host material of one or more non-adjacent ones of the layers comprises a zirconia-based phase.

8. The coating of claim 7, wherein the zirconia-based phase comprises one of zirconia -4 mol% yttria or zirconia -8 mol% yttria.

9. The coating of any of claims 1 to 5, wherein the host material of one or more non-adjacent ones of the layers comprises an aluminium-containing oxide.

10. The coating of claim 9, wherein the aluminium-containing oxide comprises a YAG-based phase, and preferably YAG.

11. The coating of claim 9, wherein the aluminium-containing oxide comprises a YAP-based phase, and preferably YAP.

12. The coating of any of claims 1 to 11, wherein the luminescent layer comprises a pyrochlore host phase which is doped with at least one luminescent dopant.

13. The coating of claim 12, wherein the at least one luminescent dopant comprises at least one of Pr and Tb.

14. The coating of claim 12 or 13, wherein the host phase is doped with between 1 mol% and 10 mol% of the at least one luminescent dopant.

15. The coating of claim 14, wherein the host phase is doped with between 1 mol% and 7 mol% of the at least one luminescent dopant.

16. The coating of claim 15, wherein the host phase is doped with between 3 mol% and 7 mol% of the at least one luminescent dopant.

-13 - 17. The coating of claim 16, wherein the host phase is doped with between 4 mol% and 6 mol% of the at least one luminescent dopant.

18. The coating of claim 17, wherein the host phase is doped with about 5 mol% of the at least one luminescent dopant.

19. The coating of any of claims 1 to 11, wherein the luminescent layer comprises a zirconia-based host phase and at least one luminescent dopant.

20. The coating of claim 19, wherein the zirconia-based host phase comprises YSZ, and preferably one of zirconia -4 mol% yttria or zirconia -8 mol%.

21. The coating of claim 19, wherein the zirconia-based host phase comprises a lanthanide-doped zirconia.

22. The coating of claim 21, wherein the lanthanide dopant comprises a single dopant selected from Dy, Er, Eu, Gd, Nd, Sm and Yb.

23. The coating of claim 21, wherein the lanthanide dopant comprises a pair of dopants selected from Gd and Er, Gd and Nd, Gd and Yb, Yb and Nd and Yb and Sm.

24. The coating of claim 19, wherein the zirconia-based host phase comprises a zirconate pyrochiore.

25. The coating of any of claims 1 to 11, wherein the luminescent layer comprises a main, host phase, and a plurality of small discrete, luminescent particles which are distributed, in this embodiment substantially uniformly, within the host phase and act, when excited by a excitation signal, to emit a luminescence signal.

-14 - 26. The coating of claim 25, wherein the luminescent particles comprise an A2B207 (pyrochiore) host which is doped with at least one luminescent dopant selected from Pr and Tb, where A comprises one or more elements from the lanthanide series (rare earth metals) or the actinide series and B comprises one or more elements from the group of transition metals.

27. The coating of claim 26, wherein the at least one luminescent dopant comprises Tb.

28. The coating of claim 26, wherein the at least one luminescent dopant comprises Pr.

29. The coating of claim 26, wherein the at least one luminescent dopant comprises Pr and Tb in combination.

30. The coating of any of claims 26 to 29, wherein the host is doped with between 1 mol% and 10 mol% of the at least one luminescent dopant.

31. The coating of claim 30, wherein the host is doped with between 1 mol% and 7 mol% of the at least one luminescent dopant.

32. The coating of claim 31, wherein the host is doped with between 3 mol% and 7 mol% of the at least one luminescent dopant.

33. The coating of claim 32, wherein the host is doped with between 4 mol% and 6 mol% of the at least one luminescent dopant.

34. The coating of claim 33, wherein the host is doped with about 5 mot% of the at least one luminescent dopant.

-15 - 35. The coating of claim 25, wherein the luminescent particles comprise a first, zirconia-based host phase, a second discrete phase, and at least one luminescent dopant.

36. The coating of claim 35, wherein the zirconia-based host phase comprises YSZ, and preferably zirconia -4 mol% yttria or zirconia - 8 mol% yttria.

37. The coating of claim 35, wherein the zirconia-based host phase comprises a lanthanide-doped zirconia.

38. The coating of claim 37, wherein the lanthanide dopant comprises a single dopant selected from Dy, Er, Eu, Gd, Nd, Sm and Yb.

39. The coating of claim 37, wherein the lanthanide dopant comprises a pair of dopants selected from Gd and Er, Gd and Nd, Gd and Yb, Yb and Nd and Yb and Sm.

40. The coating of claim 35, wherein the zirconia-based host phase comprises a zirconate pyrochlore (A2Zr2O7), where A is one or more elements selected from the lanthanide group, and preferably one or more of the elements Gd, La, Nd and Sm.

41. The coating of any of claims 35 to 40, wherein the second phase contains Y and Al.

42. The coating of claim 41, wherein the second phase includes yttria and an aluminate.

43. The coating of claim 41, wherein the second phase is a YAG-based phase, and preferably YAG.

44. The coating of claim 41, wherein the second phase is a YAP-based phase, and preferably YAP.

-16 - 45. The coating of any of claims 35 to 44, wherein the second phase is a phase which is chemically and physically stable at temperatures of up to about 1700 C, and preferably when thermally cycled.

46. The coating of any of claims 35 to 45, wherein the at least one luminescent dopant comprises one or more elements from the lanthanide series (rare earth metals), and preferably one or more elements selected from Dy, Tb, Eu, Gd, Tm and Sm.

47. The coating of claim 25, wherein the luminescent particles comprise yttria which is doped with at least one luminescent dopant.

48. The coating of claim 47, wherein the at least one luminescent dopant comprises one or more elements from the lanthanide series (rare earth metals), and preferably one or more elements selected from Dy, Tb, Eu, Gd, Tm and Sm.

49. The coating of claim 25, wherein the luminescent particles comprise a YAG-based phase, and preferably YAG, which is doped with at least one luminescent dopant.

50. The coating of claim 49, wherein the at least one luminescent dopant comprises one or more elements from the lanthanide series (rare earth metals), and preferably one or more elements selected from Dy, Tb, Eu, Gd, Tm and Sm.

51. The coating of claim 25, wherein the luminescent particles comprise a YAP-based phase, and preferably YAP, which is doped with at least one luminescent dopant.

52. The coating of claim 51, wherein the at least one luminescent dopant comprises one or more elements from the lanthanide series (rare -17 -earth metals), and preferably one or more elements selected from Dy, Tb, Eu, Gd, Tm and Sm.

53. The coating of any of claims 25 to 52, wherein the luminescent particles have a size and distribution which is such as not significantly to alter the physical or chemical characteristics of the main, structural host phase of the luminescent layer.

54. The coating of any of claims 25 to 53, wherein the luminescent particles are of a size between 1 nm and 5 pm.

55. The coating of claim 54, wherein the luminescent particles are of a size between 1 nm and 2 pm.

56. The coating of claim 55, wherein the luminescent particles are of a size between 1 nm and 1 pm.

57. The coating of claim 56, wherein the luminescent particles have a size between 1 nm and 100 nm.

58. The coating of claim 57, wherein the luminescent particles have a size between 1 nm and 10 nm.

59. The coating of any of claims 25 to 58, wherein the luminescent layer contains between 0.1 wt% and 10 wt% of the luminescent particles.

60. The coating of claim 59, wherein the luminescent layer contains between 0.1 wt% and 5 Wt% of the luminescent particles.

61. The coating of claim 60, wherein the luminescent layer contains between 0.1 wt% and 2 Wt% of the luminescent particles.

62. The coating of claim 61, wherein the luminescent layer contains between 0.1 wt% and 1 Wt% of the luminescent particles.

-18 - 63. The coating of any of ctairflS 1 to 62, wherein the coating is a TBC.

64. A coatflg subStafltV as hereiflbef0l described with reference to any of Figures 1, 2 or 3.