WO2011042052A1

WO2011042052A1 - Component with a substrate and a protective layer

Info

Publication number: WO2011042052A1
Application number: PCT/EP2009/063026
Authority: WO
Inventors: Friedhelm Schmitz; Werner Stamm
Original assignee: Siemens Aktiengesellschaft
Priority date: 2009-10-07
Filing date: 2009-10-07
Publication date: 2011-04-14

Abstract

The invention relates to a component (6) with a substrate (2) and a protective layer (9), which consists of an intermediate NiCoCrAlY layer zone (7) on or near the substrate (2) and an outer layer zone (8) arranged on the intermediate NiCoCrAlY layer zone (7), wherein the outer layer zone (8) posses the structure of the phase β-NiAl and comprises (in wt%) : 17% - 23% Al, 35% - 45% Co, and Ni balance.

Description

Component with a substrate and a protective layer

The invention relates to a component with a substrate and a protective layer, which consists of an intermediate

NiCoCrAlY layer zone on or near the substrate and an outer layer zone arranged on the intermediate NiCoCrAlY layer zone. Metallic compounds, which are exposed to high temperatures, must be protected against heat and corrosion. This is

especially true for parts of gas turbines like combustion chambers, turbine blades or vanes. These parts are commonly coated with an intermediate MCrAlY layer (M = Fe, Co, Ni) and a thermal barrier coating (TBC) which is applied on top of the intermediate layer. Between the two layers an aluminium oxide layer is formed due to oxidation.

The bonding of the three different layers is crucial for a high durability of the protection layer as a whole. Problems may arise, if there are big differences in the thermal expansion factors of the different layers. In this case failure of the thermal barrier coating might occur, which can lead to the destruction of the whole compound.

From US-PS-6, 287, 644 a continuously graded MCrAlY bond coat is known which has a continuously increasing amount of Cr, Si or Zr with increasing distance from the underlaying substrate in order to reduce the thermal mismatch between the bond coat and the thermal barrier coating by adjusting the thermal expansion factors.

The US-PS-5 , 792 , 521 shows a multi layer thermal barrier coating .

US-PS-5, 514, 482 discloses a thermal barrier coating system for super alloy components, in which the MCrAlY layer is substituted by an aluminium coating layer such as NiAl . In order to obtain the desired properties the NiAl layer has to be quite thick because of its brittleness.

From EP 1 082 216 Bl a MCrAlY layer is known, which has the γ-phase at its outer layer. This γ-phase can only be obtained by remelting or deposition from a liquid phase in an

expensive way.

EP 1 380 672 Al discloses a highly oxidation resistant component with a protective layer, which consists of an intermediate MCrAlY layer zone and an outer layer zone, having the structure of the phase β-NiAl .

In EP 1 411 148 Al a coated article is described which comprises an intermediate McRAlY layer and deposited thereon an outer layer of β-NiAl . The outer layer comprises (in wt%) : 18%-24% Al.

The layer systems mentioned above are either expensive or lack a strong bonding between the different layer zones.

It is thus an object of the present invention to describe a component having a substrate and a protective layer, which possesses a high oxidation resistance and a strong bonding between the different layer zones.

This object is met by components having an outer layer zone, which preferably comprises (in wt%) : 35% - 45% Co, and especially 14% - 23% Al and Ni balance (Matrix) . The outer layer 8 comprises the structure of γ and β-NiAl . By this high cobalt content the β-NiAl is transformed into the γ-phase and not into the γ' -phase when aluminium is depleting during operation . Surprisingly it was found that an outer layer of this

composition is able to form an extraordinary strong bonding to the intermediate layer zone. As a result the protective layer shows a high oxidation resistance and a good durability .

According to one embodiment the outer layer zone comprises (in wt%) : 15% - 19% Al, 38% - 42% Co, and Ni, especially Ni balance .

In one preferred embodiment the outer layer comprises (in wt%) : 17% Al, 40% Co and Ni balance.

Preferably the outer layer zone 8 consists of Ni, Al and Co.

The outer layer can also comprise up to 5 wt% of Cr.

This means that preferably at least 0. lwt% or more preferably at least 0,5wr% chromium is in the alloy of the outer layer 8.

Preferably the outer layer 8 consists of Ni, Al, Co and Cr.

The outer layer 8 is not a nickel based superalloy normally used as a substrate. Therefore the outer layer 8 does preferably not contain

tungsten (W)

and/or molybdenum (Mo)

and/or iron (Fe)

and/or titanium (Ti)

and/or grain boundary strengthener B, C

and/or gallium (Ga) .

It is also possible that the outer layer 8 further comprises at least one additional element selected from the group: Hf, Zr, La, Ce, Y or other elements of the Lanthanide group to improve the oxidation resistance. The maximum amount of the at least one additional element can be 1 wt% and especially is at least 0,lwt%. According to another embodiment the outer layer 8 comprises 0.4wt% - 1.0wt% of Y. The outer layer 8 may also comprise at least one of the elements selected from the group Si, Re and Ta, which improve the oxidation resistance. The outer layer can have a thickness between 3ym - lOOym, preferably 3ym - 50ym.

The intermediate NiCoCrAlY layer 7 can comprise 24% - 26% Co, 16% - 18% Cr, 9,5% - 11% Al, 0,3% - 0,5% Y, 1% - 1,8% Re und Ni, especially Ni balance.

It is also possible that the outer layer zone further

comprises (in wt%) : 0.1% - 2% Si and/or 0.2% - 8% Ta. Alternatively the intermediate NiCoCrAlY layer zone may have one of the following compositions (in wt%) :

11% - 13% Co, 20% - 23% Cr, 10.5% - 11.5% Al, 0.3% - 0.5% Y, 1.5% - 2.5% Re and Ni, especially Ni balance, especially Ni- 12Co-21Cr-llAl-0.4Y-2Re, or

11% - 13.5% Co, 19.5% - 23% Cr, 9% - 12% Al, 0.1% - 0.8% Y, 1% - 3.2% Re and Ni, especially Ni balance, especially Ni- 12Co-21-Cr-llAl-0.4Y-2Re, or

9% - 11% Co, 21% - 24% Cr, 11% - 14% Al, 0.2% - 0.9% Y and Ni, especially Ni balance.

29% - 31% Ni, 26.5% - 29.5% Cr, 6.5% - 9.5% Al, 0.3% - 0.9% Y and 0.5% - 0.9% Si and Co especially Co balance, especially Co-30Ni-28Cr-8Al-0.6Y-0.7Si, or

27% - 29% Ni, 22.5% - 25.5% Cr, 9% - 11% Al; 0.1% - 1.1% Y and Co, especially Co balance, especially Co-28Ni-24Cr-10Al- 0.6Y, or

According to one preferred embodiment of the invention Y is at least partly replaced in the intermediate NiCoCrAlY layer zone by at least one element selected from the group: Si, Hf, Zr, La, Ce or other elements of the Lanthanide group.

It was found that a thickness between 50ym to 600ym and preferably between lOOym to 300ym is an optimal for the intermediate layer zone.

Preferably the outer layer 8 zone is thinner than the

intermediate layer zone 7, preferably at least 20%.

The component according to the invention can be a part of a gas turbine like a turbine blade, a turbine vane or a heat shield. In this case an excellent protection of the turbine part against corrosion is achieved.

In the following the invention will be explained in more detail with reference to the attached drawings. In the drawings :

Figure 1 shows a heat resistant component known from the

state of the art,

Figure 2 shows an oxidation resistant component according to the invention,

Figure 3 shows a blade or a vane,

Figure 4 shows a combustion chamber and

Figure 5 shows a gas turbine.

The invention may be embodied in many different forms and should not be construed as limited to the illustrated

embodiments set forth herein. Rather, the illustrated

embodiments are provided so that this disclosure will be through and complete, and will fully convey the scope of the invention to those skilled in the art. Figure 1 shows a heat resistant component 1 known in the art. It comprises a substrate 2 which is coated with a MCrAlY layer 3. A thermally grow oxide layer (TGO) 4 is provided on the MCrAlY layer 3. The oxide layer 4 is covered by an outer thermal barrier coating (TBC) 5.

Figure 2 shows an oxidation resistant component 6 according to the invention which can be a part of a gas turbine, like a turbine blade or vane or a heat shield. Component 6 comprises a substrate 2 which can consist of a metal or an alloy, e.g. a super alloy. An intermediate NiCoCrAlY layer 7 is provided on the substrate 2. It has a composition (in wt%) of 24% - 26% Co, 16% - 18% Cr, 9.5% - 11% Al, 0.3% - 0.5% Y, 1.0% - 1.8% Re and Ni balance. The NiCoCrAlY layer 7 may contain 0.1% - 2% Si and/or 0.2% - 8% Ta.

It is possible that the NiCoCrAlY layer 7 contains additional elements like Hf, Zr, La, Ce or other elements of the

Lanthanide group. These elements can also replace part of the Y in the layer 7. The intermediate NiCoCrAlY layer 7 is approximately 200ym thick but its thickness can be in the range from 50ym to 600ym.

An outer layer 8 is provided on of the intermediate NiCoCrAlY layer 7. This outer layer 8 possesses the structure of the phases γ-Ni and β-NiAl and comprises (in wt%) : 17% - 23% Al, 35% - 45% Co and Ni (Ni-based, that means a non finished list of alloying elements), especially Ni balance. Further elements like Cr, Si, Re, Ta, Hf, Zr, La, Ce, Y and other elements of the Lanthanide group can also be included in the outer layer 8. Up to 5 wt% Cr can be part of the outer layer 8. Preferably no chromium (Cr) is used for the outer layer. Preferably the outer layer 8 comprises (in wt%) less than 0.04% C, and/or less than 0.01% H₂, and/or less than 0.02% N₂, and/or less than 0.06% 0₂. The outer layer 8 is preferably up to 50ym thick and thus thinner than the intermediate NiCoCrAlY layer zone 7 while the thickness can be in the range of 3ym to lOOym. Both layers 7, 8 can be applied by plasma spraying (VPS, APS) or other conventional coating methods. Together they form a protective layer 9.

The outer layer 8 is covered by a thermally grown oxide layer (TGO) 4, which comprises or preferably consists of a

metastable aluminium oxide, preferably having the θ-phase or a mixture of the Θ- and the γ-phase.

This θ-phase is important because it is responsible for a good adhesion for a covering ceramic coating. Once this Θ- phase is formed the phases of the still growing TGO is not so important. This can happen if no β-NiAl is present anymore because of the Al depletion.

To improve the formation of desired metastable aluminium oxide the oxidation of the outer layer zone 8 should take place at a temperature between 850°C and 1000°C, especially between 875°C and 925°C for 2h-100h, especially between 5h and 15h. Further improvements are possible, if water vapour (0.2vol% - 50vol%, especially 20vol% - 50vol. %) is added to the oxidation atmosphere or if an atmosphere is used which has a low oxygen partial pressure between 800°C and 1100°C, especially between 850°C and 1050°C. In addition to water vapour the atmosphere can also contain non-oxidating gases such as a nitrogen, argon or helium.

If the TGO 4 consists of metastable aluminium oxide it can have a needlelike structure which ensures a strong bonding between the TGO 4 and a thermal barrier coating 5 being provided on the TGO 4. The component 6 can be part of a gas turbine for example a turbine blade, a turbine vane or a heat shield.

Figure 3 shows a perspective view of a blade or vane 120, 130 which extends along a longitudinal axis 121. Along the longitudinal axis 121, the blade or vane 120, 130 has, in succession, a securing region 400, an adjoining blade or vane platform 403 and a main blade region 406. A blade root 183 which is used to secure the rotor blades 120, 130 to the shaft is formed in the securing region 400. The blade or vane root 183 is designed as a hammer head. Other configurations, for example as a firtree root or a dovetail root, are

possible. In the case of conventional blades or vanes 120, 130, solid metallic materials are used in all regions 400, 403, 406 of the rotor blade 120, 130. The rotor blade 120, 130 may in this case be produced using a casting process, a forging process, a milling process or a combination thereof. Figure 4 shows a combustion chamber 110 of a gas turbine. The combustion chamber 110 is designed, for example, as what is known as an annular combustion chamber, in which a

multiplicity of burners 107 arranged around the turbine shaft in the circumferential direction open out into a common burner chamber space. For this purpose, the overall

combustion chamber 110 is configured as an annular structure which is positioned around the turbine shaft.

To achieve a relatively high efficiency, the combustion chamber 110 is designed for a relatively high temperature of the working medium M of approximately 1000°C to 1600°C. To allow a relatively long service life to be achieved with these operating parameters, which are unfavourable for the materials, the combustion chamber wall 153 is provided, on its side facing the working medium M, with an inner lining formed from heat shield elements 155. On the working medium side, each heat shield element 155 is equipped with a

particularly heatresistant protective layer or is made from material which is able to withstand high temperatures.

Moreover, on account of the high temperatures in the interior of the combustion chamber 110, a cooling system is provided for the heat shield elements 155 and/or their holding

elements.

The materials used for the combustion chamber wall and its coatings may be similar to the turbine blades or vanes 120, 130.

The combustion chamber 110 is designed in particular to detect losses of the heat shield elements 155. For this purpose, a number of temperature sensors 158 are positioned between the combustion chamber wall 153 and the heat shield elements 155.

Figure 5 shows, by way of example, a gas turbine 100 in partial longitudinal section. In the interior, the gas turbine 100 has a rotor 103 which is mounted such that it can rotate about an axis of rotation 102.

An intake housing 104, a compressor 105, a, for example toruslike combustion chamber 110, in particular an annular combustion chamber 106, having a plurality of coaxially arranged burners 107, a turbine 108 and the exhaustgas housing 109 follow one another along the rotor 103. The annular combustion chamber 106 is in communication with an, for example annular, hotgas passage 111, where, for example, four turbine stages 112 connected in series form the turbine 108.

Each turbine stage 112 is formed from two rings of blades or vanes. As seen in the direction of flow of a working medium

113, a row 125 formed from rotor blades 120 follows a row 115 of guide vanes in the hotgas passage 111. The guide vanes 120 are in this case secured to an inner housing 138 of a stator 143, whereas the rotor blades 120 of a row 125 are arranged on the rotor 103 by way of example by means of a turbine disk 133. A generator or machine (not shown) is coupled to the rotor 103.

While the gas turbine 100 is operating, the compressor 105 sucks in air 135 through the intake housing 104 and

compresses it. The compressed air provided at the turbineside end of the compressor 105 is passed to the burners 107, where it is mixed with a fuel. The mixture is then burnt in the combustion chamber 110, forming the working medium 113.

From there, the working medium 113 flows along the hotgas passage 111 past the guide vanes 130 and the rotor blades

120. The working medium 113 expands at the rotor blades 120, transmitting its momentum, so that the rotor blades 120 drive the rotor 130 and the latter drives the machine coupled to it .

While the gas turbine 100 is operating, the components exposed to the hot working medium 113 are subject to thermal loads. The guide vanes 130 and rotor blades 120 belonging to the first turbine stage 112, as seen in the direction of flow of the working medium 113, are subject to the highest thermal loads apart from the heat shield blocks which line the annular combustion chamber 106.

To enable them to withstand the prevailing temperatures, they are cooled by means of a coolant.

The substrates may also have a directional structure, i.e. they are in singlecrystal form (SX structure) or comprise only longitudinally directed grains (DS structure) . Ironbase, nickelbase or cobaltbase superalloys are used as the material. By way of example, superalloys as known from EP 1 204 776, EP 1 306 454, EP 1 319 729, WO 99/67435 or WO 00/44949 are used; these documents form part of the present disclosure. The blades or vanes 120, 130 may also have coatings

protecting them from corrosion (MCrAlY; M is at least one element selected from the group consisting of iron (Fe) , cobalt (Co), Nickel (Ni) , Y represents Yttrium (Y) and/or silicon (Si) and/or at least one rare earth) and to protect against heat by means of a thermal barrier coating. The thermal barrier coating consists, for example, of Zr0₂, Y2O₃- Zr0₂, i.e. it is not stabilized, is partially stabilized or is completely stabilized by Yttrium oxide and/or calcium oxide and/or magnesium oxide.

Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as electron beam physical vapor deposition (EBPVD) . The guide vane 130 has a guide vane root (not shown here) facing the inner housing 138 of the turbine 108 and a guide vane head on the opposite side from the guide vane root. The guide vane head faces the rotor 103 and is fixed to a

securing ring 140 of the stator 143.

Claims

1. Component (6) with

a substrate (2) and

a protective layer (9),

which comprises

an intermediate

NiCoCrAlY layer (7) direct on or over the substrate (2) and an outer layer (8) arranged direct on or over the

intermediate NiCoCrAlY layer zone (7),

wherein the outer layer zone (8) is Ni based

and comprises a γ-structure and β-NiAl-structure

and preferably comprises (in wt%) :

35% - 45% Co,

especially 36% - 44% Co

and Ni .

2. Component (6) according to claim 1,

wherein the outer layer (8) comprises (in wt%) :

38% - 42 % Co

especially 40% Co,

and Ni .

3. Component (6) according to claim 1 or 2

wherein the outer layer (8) comprises at least 0. lwt% Chromium (Cr) ,

especially at least 0.5wt% Cr,

and very especially at least 1.0wt% Cr.

4. Component (6) according to claim 1, 2 or 3,

wherein the outer layer (8) further comprises (in wt%) up to 10% Cr,

preferably up to 5% Cr.

5. Component (6) according to claim 1, 2, 3 or 4,

wherein the outer layer (8) comprises 14wt% - 23wt% Al, especially 14wt% - 19wt% Al .

6. Component (6) according to claim 1, 2, 3 or 4,

wherein the outer layer (8) comprises 14wt% - 17wt% Al .

7. Component (6) according to any of the preceding claims, wherein the outer layer (8) further comprises at least one additional element selected from the group consisting of Hf, Zr, La, Ce, Y and other elements of the Lanthanide group.

8. Component (6) according to claim 7,

wherein the maximum amount of the at least one additional element is 1 wt% and especially at least 0,lwt%.

9. Component (6) according to claim 7 or 8,

wherein the outer layer (8) comprises (in wt%) 0.4% - 1.0% Y.

10. Component (6) according to any of the preceding claims, wherein the outer layer (8) further comprises at least one of the elements selected from the group Si, Re and Ta.

11. Component according to claim 1, 2, 5 or 6,

wherein the outer layer (8) consists of Ni, Al and Co.

12. Component according to claim 1, 2, 3, 4, 5 or 6, wherein the outer layer (8) consists of Ni, Al, Co and Cr.

13. Component (6) according to any of the preceding claims, wherein the outer layer (8) has a thickness between 3ym to lOOym, preferably between 3ym to 50ym.

14. Component (6) according to any of the preceding claims, wherein the intermediate NiCoCrAlY layer (7) comprises (in wt%) :

24% - 26% Co,

16% - 18% Cr,

9.5% - 11% Al,

1.0% - 1.8% Re

0.3% - 0.5 Y,

and Ni

15. Component (6) according to any of the claims 1 to 15, wherein the intermediate NiCoCrAlY layer (7) comprises (in wt%) :

11% - 13% Co,

20% - 23% Cr,

10.5% - 11.5% Al,

1.5% - 2.5% Re

0.3% - 0.5 Y,

and Ni, especially 12% Co, 21% Cr, 11% Al, 2% Re, 0.4% Y and Ni .

16. Component (6) according to any of the claims 1 to 13, wherein the intermediate NiCoCrAlY layer (7) comprises (in wt%) : 11% 13.5% Co,

19. 23% Cr,

9% 12% Al,

1% 3.2% Re

0.1 0.8 Y,

and

17. Component (6) according to any of the claims 1 to 13, wherein the intermediate NiCoCrAlY layer (7) comprises (in wt%) :

9% - 11% Co,

21% - 24% Cr,

11% - 14% Al,

0.2% - 0.9 Y,

and Ni .

18. Component (6) according to any of the claims 1 to 13, wherein the intermediate NiCoCrAlY layer (7) comprises (in wt%) : 29% - 31% Ni,

26.5% - 29.5% Cr,

6.5% - 9.5% Al,

0.3% - 0.9 Y,

0.5% - 0.9 Si

and Co, especially 30% Ni, 28% Cr, 8% Al, 0.6% Y, 0.7% Si and Co.

19. Component (6) according to any of the claims 1 to 13, wherein the intermediate NiCoCrAlY layer (7) comprises (in wt%) : 27% - 29% Ni,

9% - 11% Al,

0.1% - 1.1 Y,

and Co, especially 28% Ni, 24% Cr, 10% Al, 0.6 Y and Co.

20. Component (6) according any of the claim 14, 15, 16, 17, 18, 19,

wherein the intermediate NiCoCrAlY layer (7) further

comprises (in wt%) : 0.1% - 2% Si and/or 0.2% - 8% Ta.

21. Component (6) according any of the claims 14 to 20, wherein in the intermediate NiCoCrAlY layer (7) Y is at least partly replaced by at least one element selected from the group consisting of Si, Hf, Zr, La, Ce and other elements of the Lanthanide group.

22. Component (6) according to any of the preceding claims, wherein the intermediate NiCoCrAlY layer (7) has a thickness of 50ym to 600ym, preferably lOOym to 300ym.

23. Component (6) according to any of the preceding claims, wherein the outer layer (8) is thinner than the intermediate

NiCoCrAlY layer (7), especially at least 20% thinner.

24. Component (6) according to any of the preceding claims, wherein the metallic protective layer consists of two layers

25. Component (6) according to any of the preceding claims, wherein the outer layer (9) zone (8) consists of a γ and β- NiAl structure.

26. Component according to any of the preceding claims, wherein the outer layer (8) does not contain iron (Fe) .

27. Component according to any of the preceding claims, wherein the outer layer (8) does not contain chromium (C

28. Component according to any of the preceding claims, wherein the outer layer (8) does not contain carbon (C)

29. Component according to any of the preceding claims, wherein the outer layer (8) does not contain Gallium (Ga)

30. Component according to any of the preceding claims, wherein the outer layer (8) does not contain Bor (B) .

31. Component according to any of the preceding claims, wherein the outer layer (8) does not contain Molybdenum (Mo)

32. Component according to any of the preceding claims, wherein the outer layer (8) does not contain Silicon (Si;

33. Component according to any of the preceding claims, wherein the outer layer (8) does not contain tungsten (

34. Component according to any of the preceding claims, wherein the outer layer (8) does not contain titanium (Ti) .