NICOCRALY-ALLOY, A POWDER, A COATING AND A COMPONENT

Description

[0001] The invention relates to a composition of a NiCoCrAlY based alloy especially used for gas turbines, a powder, a coating and a component.

[0002] When further increasing engine efficiency, output power, availability, and reliability in the current gas turbine development, it is often limited by temperature capacity and lifetime of protective coatings for protection against hot corrosion and oxidation and bonding thermal barrier coating TBC on the hot turbine components. The used coatings were all developed more than 10 years ago and can not fulfil demands of further turbine development. In the MCrAlY coatings available today, one relies on Yttrium (Y) incorporation very much to have pegging and scavenge effects to increase oxidation and corrosion resistances of the coatings. However, it has recently been reported that Yttria inclusions in the protective aluminum oxide scale on top of MCrAlY provide fast oxygen diffusion routes, and therefore, accelerate oxidation of the coating (Nijdam TJ, Sloof WG. Acta Materialia 2007;55:5980).
High content of Sulfur > 10ppm existed in the current MCrAlY shortens coating lifetime (Smialek JL, Jayne DT, Schaeffer JC, Murphy WH. Thin Solid Films 1994;253:285; and Smialek JL. Metallurgical Transactions A, Physical Metallurgy and Materials Science 1991;22A:739). In addition, the increase in oxidation and corrosion lifetime of the MCrAlY coatings is often achieved in expense of their mechanical durability. The development of advanced turbines with flexible operations demands coatings withstanding operations with both higher temperature and longer time exposure and higher mechanical loadings.

[0003] This problem has not been solved yet.

[0004] It is therefore aim of the invention to overcome the problems mentioned above.

[0005] The problem is solved by an alloy of claim 1, by a powder of claim 2, a coating by claim 3 and a layer system according to claim 4.

[0006] Further advantages of the invention are listed in the dependent claims which can be combined arbitrarily with each other to yield further advantages.

[0007] This invention is to solve the problem by using recent research results and upgraded thermodynamic modelling to design an optimized and innovative NiCoCrAlX alloy coatings applied by means of thermal spraying in air, vacuum, or protected atmosphere, physical deposition, and plating on Ni or Co based superalloys.
X is a combination of minor elements such as Y, Ru, Ir, Si, Hf, Ta and etc. instead of Yttrium (Y) in the current NiCoCrAlY coatings. It means that we will introduce other minor elements to replace part of Yttrium (Y) functions in order to keep Yttrium (Y) content low. Introduction of Ruthenium (Ru) and Iridium (Ir) reduces diffusion rate of Aluminum (Al) and forms diffusion barrier to minimize the interdiffusion between NiCoCrAlX coating and substrates. Ru addition increases mechanical durability of the coatings.
Moreover, another approach in designing and manufacturing the innovative NiCoCrAlX coatings is reduce S content to ≤10ppm to further increase coating lifetime. The coating thickness should be in the range of 30-800 µm depending on type of applications and application methods.

[0008] The new NiCoCrAlX coating is Ni-based and possesses the preferred following composition (in wt%):

Ni balanced,

25.7 % - 27.3% Cobalt (Co),

15.0% - 16.0% Chromium (Cr),

12.2% - 13.2% Aluminum (Al),

0.3% - 0.5% Yttrium (Y),

2.5% - 3.5% Ruthenium (Ru),

and

optionally

0.4% - 0.8% Silicon (Si),

0.4% - 0.6% Tantalum (Ta),

0.4% - 0.6% Molybdenum (Mo).

[0009] This invention results in NiCoCrAlYRu, NiCoCrAlYRuSi, NiCoCrAlYRuTa, NiCoCrAlYRuMo, NiCoCrAlYRuSiTa, NiCoCrAlYRuSiMo, NiCoCrAlYRuTaMo, NiCoCrAlRuMoSiTa coatings with a higher temperature capacity, longer life, and larger mechanical durability than the NiCoCrAlY coatings available today.

[0010] A powder with this alloy composition can be mixed with a binder and/or refractory metals or ceramics if used as an abrasive coating.

[0011] For turbine application especially a metallic substrate like a nickel or cobalt based superalloy is used on which the inventive coating is applied on.

[0012] The coating is applied especially by the thermal spray and electron beam vapor deposition processes.

[0013] Even SLM, SLS or any AM technique is possible to apply coatings or to produce components of this alloy or used as repair material.

[0014] A layer system therefore at least comprises
a metallic substrate,
especially a Nickel based superalloy and
at least a coating with the inventive alloy and optionally a ceramic layer on top the metallic bond and oxidation coating.

[0015] The ceramic layer comprises preferably a Zirconia based composition, partly or fully stabilized.

Claims

1. Nickel-based alloy,
and least comprising (in wt%),
especially consisting of:

Cobalt (Co) 25.7% - 27.3%

especially 26.5%

Chromium (Cr) 15.0% - 16.0%

especially 15.5%

Aluminum (Al) 12.2% - 13.2%

especially 12.7%

Yttrium (Y) 0.3% - 0.5%

especially 0.4%

Ruthenium (Ru) 2.5% - 3.5%

especially 3.0%

optionally

Molybdenum (Mo) 0.4% - 0.6%

especially 0.5%

Silicon (Si) 0.4% - 0.8%

especially 0.6%

Tantalum (Ta) 0.4% - 0.6%

especially 0.5%,

optionally Sulfur (S) ≤ 10ppm.

2. Alloy
comprising NiCoCrAlYRu, NiCoCrAlYRuSi, NiCoCrAlYRuMo, NiCoCrAlYRuTa, NiCoCrAlYRuSiTa, NiCoCrAlYRuSiMo, NiCoCrAlYRuTaMo or NiCoCrAlYRuSiTaMo.

3. Powder,
comprising,
especially consisting of,
an alloy according to claim 1 or 2,
optionally comprising a binder and/or ceramic particles.

4. Coating,
having a composition of an alloy according to claim 1, 2 or
produced with powder of claim 3,
especially having a thickness in the range of 30µm to 800µm.

5. Component,
comprising
a metallic substrate,
especially Nickel-based or Cobalt-based superalloy,
a metallic coating with a composition according to claim 1, 2
or
a coating according to claim 4,
and optionally
a ceramic coating above the substrate and the metallic coating.