COATING SYSTEM, METHOD OF COATING A SUBSTRATE, AND GAS TURBINE COMPONENT

1 . A coating system for a superalloy substrate, comprising

an inner coating layer,

an intermediate coating layer and

an outer coating layer,

wherein

the inner coating layer is an aluminide layer;

the intermediate coating layer is a diffusion layer comprising Cr, Al, Ni and Co, where the Cr-content is between 15% by weight and 30% by weight; and

the outer coating layer is a Cr-free diffusion layer comprising Al and Ni, where the Al-content is between 15% by weight and 30% by weight.

2 . The coating system as claimed in claim 1 ,

wherein the Cr-content of the intermediate coating layer is between 18% by weight and 22% by weight and/or

wherein the Al-content of the outer coating layer is between 18% by weight and 22% by weight.

3 . The coating system as claimed in claim 1 ,

wherein the Al-content of the intermediate coating layer is between 4% by weight and 12% by weight and/or

wherein the Co-content of the intermediate coating layer is between 5% by weight and 15% by weight.

4 . The coating system as claimed in claim 1 ,

wherein the intermediate coating layer comprises

up to 1% by weight Y and/or

up to 2% by weight Si and/or

up to 1% by weight Hf, and/or

wherein the outer coating layer comprises

up to 1% by weight Y and/or

up to 2% by weight Si and/or

up to 1% by weight Hf.

5 . The coating system as claimed in claim 4 ,

wherein the intermediate coating layer comprises by weight:

8% to 12% Co,

18% to 22% Cr,

8% to 12% Al,

0% to 2% Si,

0% to 1% Y,

0% to 1% Hf,

rest Ni.

6 . The coating system as claimed in claim 4 ,

wherein the outer coating layer comprises by weight:

18% to 22% Al,

0% to 2% Si,

0% to 1% Y,

0% to 1% Hf,

rest Ni.

7 . A gas turbine component comprising

a surface and a coating system according to claim 1 on the surface.

8 . The gas turbine component as claimed in claim 7 ,

wherein the surface underlying the coating system is a chromised or platinised.

9 . A method of coating a substrate with a coating system, comprising:

aluminising the surface of the substrate to form an inner coating layer;

applying a slurry with a solid content comprising Cr, Al, Ni and Co onto the inner coating layer, where the Cr-content of the solid content is between 15% and 30% by weight of the solid content, and diffusion heat treating the slurry applied to the inner coating layer at a temperature above 800° C. for 1 to 8 hours to form an intermediate coating layer; and

applying a Cr-free slurry with a solid content comprising Al and Ni onto the intermediate coating layer, where the Al-content of the solid content is between 15% and 30% by weight of the solid content, and diffusion heat treating the slurry applied onto the intermediate surface layer at a temperature above 800° C. for 1 to 8 hours to form an outer coating layer.

10 . The method as claimed in claim 9 ,

wherein the slurry applied onto the inner coating layer and/or the slurry applied onto the intermediate coating layer is/are diffusion heat treated at a temperature above 850° C.

11 . The method as claimed in claim 9 ,

wherein the slurry applied onto the inner coating layer and/or the slurry applied onto the intermediate coating layer is/are diffusion heat treated for 2 to 4 hours.

12 . The method as claimed in claim 9 ,

wherein the surface of the substrate is platinised before it is aluminised.

13 . The method as claimed in claim 12 ,

wherein the surface of the substrate is platinised by platinum plating the surface and heat-treating the platinum plated surface.

14 . The method as claimed in claim 12 ,

wherein the surface of the substrate is chromised before it is platinised.

15 . The method as claimed in claim 9 ,

wherein the slurry applied onto the inner coating layer comprises an ethanol carrier or an acid based carrier, and/or

the slurry applied onto the intermediate coating layer comprises an ethanol carrier or an acid based carrier.