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Title:
COATING, COATING LAYER SYSTEM, COATED SUPERALLOY COMPONENT
Document Type and Number:
WIPO Patent Application WO/2013/056935
Kind Code:
A1
Abstract:
The invention relates to a coating, a coating layer system and a coated superalloy component preferably to be used in a gas turbine's hot gas path. Today' s MCrAlY coatings rely very much on yttrium incorpora¬ tion to have so called pegging and scavenge effects to in- crease oxidation and corrosion resistance of the coatings. It is proposed following MCrAlX coatings consisting of: Nickel based coating consisting of: 15 to 40 wt% Co, 10 to 25 wt% Cr, 5 to 15 wt% Al, 0,05 to 1 wt% Y and/or at least one of elements from LA series, 0,05 to 8 wt% Ru or Fe, 0 to 1 wt% Ir, 0,05 to 5 wt% Mo, 0 to 3 wt% Si, 0 to 5 wt% Ta, 0 to 2 wt% Hf, and unavoidable impurities, and a balance of nickel. Cobalt based coating consisting of: 15 to 40 wt% Ni, 15 to 28 wt% Cr, 5 to 15 wt% Al, 0,05 to 1 wt% Y and/or at least one of elements from La series, 0,05 to 5 wt% Ru and/or Mo, 0 to 2 wt% Ir, 0 to 3 wt% Si, 0 to 5 wt% Ta, Hf and unavoidable impurities, and a balance of cobalt.

Inventors:
LI XIN-HAI (SE)
Application Number:
PCT/EP2012/068304
Publication Date:
April 25, 2013
Filing Date:
September 18, 2012
Export Citation:
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Assignee:
SIEMENS AG (DE)
International Classes:
C23C28/00; C23C30/00
Domestic Patent References:
WO2006025865A22006-03-09
Foreign References:
EP1783236A12007-05-09
EP2145969A12010-01-20
Other References:
NIJDAM TJ; SLOOF WG., ACTA MATERIA/IA, vol. 55, 2007, pages 5980
SMIALEK JL; JAYNE QT; SCHAEFFER JC; MURPHY WH, THIN SOLID FILMS, vol. 253, 1994, pages 285
SMIALEK JL, METALLURGICAL TRANSACTIONS A. PHYSICAL METALLURGY AND MATERIAL SCIENCE, vol. 22A, 1991, pages 739
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Claims:
Patent claims

1. Nickel based coating

15 to 40 weight percent cobalt,

10 to 23 weight percent chromium,

5 to 15 weight percent aluminum,

0,05 to 1 weight percent yttrium and/or at least one of elements from lan thanum series,

0,05 to 5 weight percent ruthenium,

0 to 2 weight percent iridium,

0,05 to 5 weight percent molybdenum,

0 to 3 weight percent silicon,

0 to 20 weight percent iron

0 to 5 weight percent tantalum,

0 to 2 weight percent hafnium,

and unavoidable impurities,

and a balance of nickel.

2. Coating according to Claim 1, containing 0,1 to 0,6 weight percent of silicon. 3. Coating according to one of Claim 1 to 2, containing 0,3 to 0,7 weight percent of tantalum.

4. Coating according to one of Claims 1 or 3, containing 0,1 to 0,5 weight percent of hafnium.

5. Coating layer according to one of Claims 1 to 4, wherein the content of sulfur is reduced to below lOppm (parts per million) .

6. Coating layer according to one of Claims 1 to 5, wherein the thickness of the coating is between 30 - 800 ym.

7. Coating layer system comprising a lower first layer on a substrate and an adherent upper second layer, wherein the first layer is a coating according to one of the claims 1 to 6 and the second layer is a ceramic coating or multiple ce¬ ramic coatings.

8. Coating layer system according to claim 7, wherein each of ceramic coatings consists of

zirconium dioxide

and a stabilizer.

9. Coating layer system according to claim 7, wherein the stabilizer is at least one of yttrium oxide, magnesium oxide, and oxides of elements in lanthanum series.

10. Coated superalloy component comprising

- a substrate article formed of a superalloy and

- an adherent coating according to one of the claims 1 to 6 or

- an adherent coating layer system according to one of the claims 8 to 9

covering at least a portion of the substrate article's sur¬ face . 11. Coated superalloy component according to claim 11, where¬ in the superalloy component is a blade, a vane, or a sealing segment of a gas turbine's hot gas path.

Description:
Description

Coating, coating layer system, coated superalloy component

The invention relates to a coating, a coating layer system and a coated superalloy component preferably to be used in a gas turbine's hot gas path. When further increasing engine efficiency, output power, availability and reliability in the current gas turbine de ¬ velopment, this effort is often limited by temperature capac ¬ ity and lifetime of protective coatings for protection against hot corrosion and oxidation and bonding thermal bar- rier coating on the hot turbine components. The currently used coatings are so called MCrAlY coatings developed by ma ¬ jor gas turbine manufactures. Most gas turbine manufactures use there proprietary coatings since commercially available coatings are much less effective.

The term MCrAlY coatings is widely applied, wherein M means cobalt or nickel or a mixture of cobalt and nickel. These coatings may be used as corrosion resistant overlays or as bond-coats for use with thermal barrier coatings. Since in the first and second stage of a gas turbine metal tempera ¬ tures may exceed 850°C two predominant corrosion mechanics have been identified to be accelerated. One is the high tem ¬ perature oxidation occurring at temperatures above 950 °C and the other mechanism is the so called type-I-hot-corrosion- occurring at aproximately 850°C to 950°C.

During the last ten years the demand for coatings in gas tur ¬ bines increased, which led to an increase in price of the coatings, which contain comparatively large amounts of rare earth or minor elements which' s availability is increasingly tight . Today' s MCrAlY coatings rely very much on yttrium incorpora ¬ tion to have so called pegging and scavenge effects to in ¬ crease oxidation and corrosion resistance of the coatings. However, it has been recently found that the yttrium content in MCrAlY may not be optimized. Nijdam TJ, Sloof WG. (Acta Materia/ia 2007 ; 55 : 5980 ) reported that yttrium oxide inclu ¬ sions in the protective aluminum oxide scale on top of the MCrAlY provide fast oxygen diffusion routes and therefore ac- celerate oxidation of the coating.

Further Smialek JL, Jayne QT, Schaeffer JC and Murphy WH (Thin Solid Films 1994; 253:285; Smialek JL; Metallurgical Transactions A. Physical Metallurgy and Material Science 1991 ; 22A: 739) state that a high sulfur content of bigger than lOppm (parts per million) existed in the current MCrAlY layer shortening coating lifetime.

Typically ceramic coating (s) are used on a hot gas component of a gas turbine, for example turbine blades, combustors, transition ducts, sealing segments, and nozzle guide vanes, providing the components with thermal insulating or sealing functions. For the thermal insulating, the ceramic coatings are called thermal barrier coatings (TBC) which are charac- terized by a low thermal conductivity and typically consist of zirconia stabilized by yttria generally deposited by plasma spraying and electron beam physical vapor deposition on the substrate. Often a bond-coat is necessary to avoid ex ¬ ceeding residual stresses caused by different thermal expan- sion of the substrate and the ceramic thermal barrier coat ¬ ing (s) . Most often the bond-coat is applied on the surface as a MCrAlY bond-coat.

It is one task of the invention to optimize the coating con- stitution, in order to achieve a good thermal stability of coating phase structures and a high mechanical durability. It is another task to optimize the content and combination of the rare earth and minor elements in coatings, in order to minimize growths of oxides on top of the coating and inter- diffusion between coating and superalloy substrates which lead to a rapid consumption of the Al reservoir in coatings thereby coating lifetime.

It is still another task of the invention to avoid the imple ¬ mentation of sulfur in the coating system shortening the coating lifetime.

To overcome the technical limitations outlined above and as a reaction to the dramatic increase in price of rare earth ele ¬ ments a coating according to claim 1, a coating layer system according to claim 7 and a coated superalloy component espe- cially a blade, a vane, or a sealing segment of a gas turbine hot gas path is proposed according to the invention. The re ¬ spectively dependent claims refer to preferred embodiments of the invention. By introduction of other minor elements like ruthenium, iridium, molybdenum, silicon, hafnium, tantalum, and elements in lanthanum series the necessary amount of yttrium is significantly reduced, which efficiently minimize the negative ef ¬ fects of yttrium. The coating and coating system according to the invention can be characterized by the term MCrAlX alloy coating, wherein M stands for nickel or cobalt or both of these elements and X is a combination of minor elements such as yttrium, ruthenium, iridium, silicon, hafnium, or tantalum and others .

The new coating alloy according to the invention performs in a very efficient way because the introduction of ruthenium, molybdenum, or/and iridium reduces the diffusion rate of aluminum and forms a diffusion barrier to minimize the inter- diffusion between the MCrAlX coating and the substrate. A preferred embodiment of the coating layer according to claim 1 provides a reduction of the sulfur content to below lOppm which increases the coating lifetime. Preferably the coating is applied in a thickness in the range of 30 to 800 um depending on the type of application and the application method. Preferred application methods are thermal spraying in air, thermal spraying in vacuum, thermal spraying in protected atmosphere, physical vapor deposition, and plating on nickel or cobalt based superalloys.

The coating according to one of the claims 1 to 6 can be ap ¬ plied as a single coating or as a bond-coat underlying an ad ¬ herent ceramic coating (s) compensating different thermal ex- pansions between the substrate and the ceramic coating (s) on the one hand and improving especially the oxidation resis ¬ tance of the superalloy component.

Summarizing this invention results in MCrAlX (as defined above) coatings with a higher temperature capacity and longer lifetime compared to conventional MCrAlY coatings.

The following relates to preferred embodiments of the inven ¬ tion with reference to drawings illustrating the currently best mode of putting the invention into practice.

Figure 1 shows a first embodiment of the invention,

wherein the coating to the invention is applied as a single layer to a substrate and

Figure 2 shows a second embodiment of the invention, wherein the coating according to claim 1 is an intermediate layer of a coating layer system to be applied on a substrate.

Figure 1 shows a substrate as covered with an adherent coat ¬ ing C of a consistency outlined in claim 1. The coating C is applied on a substrate by way of thermal spraying in air or vacuum or protected atmosphere or by way of physical vapor deposition or by way of plating. The substrate is part of a superalloy gas turbine component, for example a gas turbine vane or a gas turbine blade or a combustor part.

Figure 2 shows a substrate covered at least partially by a layer system comprising a coating as a lower layer directly provided on the substrate, which coating C is an intermediate layer provided as a bond-coat for the adherent ceramic coat ¬ ing (s) TBC . The coating C has the composition outlined in claim 1. The substrate is a blade or a vane or a combustor part or a sealing segment of a gas turbine exposed to the hot gas .

The ceramic coating (s) consist of at least 70wt~6 zirconium oxide and is stabilized by at least one of yttrium oxide, magnesium oxide, and oxides of elements in lanthanum series. The bond-coat compensates different thermal expansion between the ceramic coating (s) and the superalloy substrate.