Nickel based superalloy with high oxidation resistance, high corrosion resistance and good processability

The invention relates to Nickel-based superalloys with high oxidation resistance, high corrosion resistance and good pro- cessability.

There is always a need to increase the combination of perfor- mance, robustness and fuel flexibility of our gas turbines. The key to this is to improve material systems in the hot stage turbine components. Improved robustness requires an im- proved ability to suppress corrosion and oxidation assisted crack propagation.

A coating cannot by definition protect a crack, hence this implies a need for improved combinations of bare corrosion and oxidation resistance. Higher bond coat temperatures with retained or reduced top coat spallation in TBC (Thermal Bar- riers Coating) would provide improved component performance. Hence there is a need for new base alloys with improved com- binations of bare corrosion and oxidation resistance as well as improved coating compatibility. These alloys must also have useful mechanical properties and processability.

Classical Industrial Gas Turbine (IGT) alloys for turbine blades and vanes such as IN792, IN738LC and PWA1483 score well in corrosion resistance and processability, but less so in terms of oxidation resistance and coating compatibility. Aero alloys such as Alloy247LC and CMSX-4 score well in terms of oxidation resistance and coating compatibility, but less so in terms of corrosion resistance and their small Heat Treatment Windows (HTW) reduce their processability.

New IGT alloys STAL15SX and STAL125 combine the oxidation and coating compatibility of the Aero alloys with the corrosion resistance of the IGT alloys, and, also show larger HTW val- ues than Aero or IGT alloys. But there is a need to have new IGT alloys with even better coating compatibility and bare oxidation resistance than what have already been designed.

It is therefore the aim of the invention to overcome the problems of the state of the art as listed above and improve Nickel-based superalloys.

The problem is solved by an alloy according to claim 1, a powder according to claim 22 and a component according to claim 23.

In the dependent claims further advantages are listed which can be combined arbitrarily with each other to yield further advantages .

CC means a polycrystalline structure, DS means a columnar structure and SX means single crystal structure.

Compared to the current alloys for IGT there is the idea to partly or fully replace Cobalt (Co) by Iron (Fe) and partly replace Tantalum (Ta) by (or by more) Hafnium (Hf) to improve the bare oxidation resistance and the coating compatibility while retaining the large heat treatment window despite the addition of more Hafnium (Hf).

As an example:

The CC alloy STAL125CC has a nominal composition (in wt%) of: Ni-5Co-12.5Cr-1 .5Mo-3.5W-5.5Al-8Ta-0.5Hf-0.07C-0.015B-0.01Zr; which is transformed into

Ni-3Co-4Fe-12 .5Cr-1.5Mo-3.5W-5.6Al-6Ta-1.5Hf-0.07C-0.015B-0.01Zr.

The Aluminum (Al) activity at 1273K is increased by 49%, while the HTW is increased from 75K to 100K.

The addition of Hafnium (Hf) enables the alloy to be used for CC as well as DS casting. When it diffuses into a bond coat of the substrate it will suppress the rumpling via strength- ening of the beta phase, and this will suppress the spalla- tion of the ceramic top coat.

The addition of iron (Fe) will reduce the gamma prime solvus temperature to such an extent that it more than compensates for the reduction in the HTW due to the Hafnium (Hf) addi- tion.

The addition of Iron (Fe) also increases the Aluminum (Al) activity, and this improves the bare oxidation resistance, and, reduces the loss of Aluminum (Al) from the bond coat in- to the base alloy via interdiffusion, enabling higher bond coat temperatures.

As a further example: If a SX-alloy is tie line scaled to 12.5%Cr by keeping the matrix and particles compositions con- stant while the fraction of gamma prime phase is increased until the content of Chromium (Cr) has been reduced to 12.5%Cr to improve the creep strength we get: Ni-4.6Co-12 .5Cr-0.9Mo-3.7W-5.4Al-9.1Ta-0.1Hf-0.25Si.

With the same type of transformation where Iron (Fe) is added and Hafnium (Hf) increased while Tantalum (Ta) and Cobalt (Co) are reduced we get:

Ni-3Co-4Fe-12 .5Cr-1.3Mo-3W-5.4A1-6.5Ta-1.5Hf-0.25Si.

The Aluminum (Al) activity at 1273K is increased by 43%.

These are preliminary composition limits for a patent appli- cation:

Then there should probably be a few additional refinements resulting in a few preferred embodiments.

Reactive Elements (RE) are some combination of Sulfur neu- tralizers like Ce, La, Y, Dy,....

The technical inventive step is the use of Iron (Fe) to in- crease the activity of Aluminum (Al) and the heat treatment window, despite the addition of more Hafnium (Hf) for coating compatibility and improved DS castability.

It will be possible to tolerate higher bond coat temperatures and more frequent cycling. A beneficial side effect is that the HIP/solutioning temperature can be reduced from the 1523K to 1553K used in the New IGT alloys to 1473K (1200°C) as ef- fect of the reduced gamma prime solvus temperature thanks to additional Iron (Fe) . A reduced HIP/solutioning temperature broadens the number of HIP vendors able to do this.

Another beneficial side effect is that Cobalt (Co) is a prob- lematic element in terms of health and safety, and reduced Co levels are thus advantageous.

A further and important advantage is that replacement of Tan- talum (Ta) by Hafnium (Hf) decreases the density.

Better components thanks to more design freedom. Easier pro- curement because of HIP at reduced temperatures.

Advanced laser cladding with fillers having extremely high oxidation resistance and coating compatibility to pre-empt oxidation and spallation of the top coat at 'tips and edges' where the temperatures tend to be especially high, i.e. the use of hybrid components.

The inventive alloy comprises (in wt%) :

Cobalt (Co) 0.0 - 5.0, especially until 4.0,

Iron (Fe) 1.5 - 6.5, especially 2.5 - 4.5, Chromium (Cr) 12.0 - 14.0,

Molybdenum (Mo) 1.0 - 2.0, especially 1.1 - 1.6,

Wolfram (W) 2.0 - 5.0, especially 2.5 - 4.0,

Aluminum (Al) 5.2 - 5.8,

Tantalum (Ta) 5.0 - 7.0, especially 6.0 - 7.0,

Hafnium (Hf) 1.2 - 1.8, optionally Carbon (C) 0.005 - 0.1,

Silicon (Si) 0.005 - 0.4,

Boron (B) >0 - 0,02, especially 0.005 - 0.02, Zirconium (Zr) >0 - 0,05, especially 0.005 - 0.05,

0, 0 - 0,05 reactive element (s) , especially Cerium (Ce) , Yttrium (Y) , Lanthanum (La) and/or Dysprosium (Dy) , Ni based.

A large blade has a weight larger than 1.0kg, especially heavier than 1.5kg.

A small blade has a weight smaller than 1.0kg, especially smaller than 0.8kg.

For small or large blades both in a SX structure the alloy comprises 0,1wt% - 0,4wt% Silicon (Si) .

For small and large blades in a CC or DS structure the alloy comprises especially 0,005wt% - 0,015wt% Silicon (Si) . For small blades in a SX structure the alloy comprises espe- cially 0,005wt% – 0,03wt% Carbon (C). For large blades in a SX structure the alloy comprises espe- cially 0,03wt% – 0,07wt% Carbon (C). For small and large blades in a CC or DS structure the alloy comprises especially 0,03wt% – 0,1wt% Carbon (C). For small blades in a SX structure the alloy comprises espe- cially maximum 0,005wt% Boron (B). For large blades in a SX structure the alloy comprises espe- cially 0,005wt% - 0,015wt% Boron (B). For small and large blades in a CC or DS structure the alloy comprises 0,005wt% – 0,02wt% Boron (B). For small and large blades in a CC or DS structure the alloy comprises 0,005wt% – 0,05wt% Zirconium (Zr). For small or large blades in a SX structure the alloy com- prises maximum 0,01wt% Zirconium (Zr).