Method for applying a coating to a surface of a mullite material, mullite material having a coating, and gas turbine component
A method for applying a coating 1 to a surface 2 of a mullite material 3 is specified, which comprises pretreating the surface 2 of the mullite material 3 by means of a plasma-chemical process in which molecular hydrogen is excited in such a way that plasma-activated hydrogen is produced S 1 , and applying an aluminum oxide-containing layer 4 by means of a PVD process to the pretreated surface 2 of the mullite material 3 S 2 . Furthermore, a mullite material 3 with a coating and a gas turbine component with such a mullite material 3 are specified.
1. A method for applying a coating to a surface of a mullite material comprising:
pre-treating the surface of the mullite material using a plasma-chemical process in which molecular hydrogen is excited in such a way that plasma-activated hydrogen is produced, and
applying an aluminum oxide-containing layer on the pretreated surface of the mullite material using a PVD process.
2. The method according to claim 1 , wherein the pretreatment is carried out using the plasma-chemical process in such a way that silicon is removed from silicon-containing phases of the surface of the mullite material.
3. The method according to claim 1 , wherein the pretreatment using the plasma-chemical process is carried out in such a way that the pretreated surface of the mullite material comprises α-Al 2 O 3 .
4. The method according to claim 1 , wherein the plasma-chemical process is carried out at a total pressure between 5×10 −3 mbar and 5×10 −2 mbar.
5. The method according to claim 1 , wherein the PVD process is reactive cathodic spark evaporation or sputtering.
6. The method according to claim 1 , wherein the aluminum oxide-containing layer is applied as an essentially single-phase layer.
7. The method according to claim 1 , wherein the aluminum oxide-containing layer is deposited as a layer with metallic macroparticles.
8. The method according to claim 1 , wherein the aluminum oxide-containing layer comprises at least one of the group consisting of chromium, titanium, hafnium, yttrium, erbium, silicon and zirconium.
9. The method according to claim 1 further comprising:
heat treating the applied aluminum oxide-containing layer at a temperature in the range between 900° C. and 1400° C. for a time period between 15 min and 60 min.
10. The method according to claim 1 further comprising:
oxidizing the applied aluminum oxide-containing layer using an oxygen plasma.
11. The method according to claim 1 further comprising:
infiltrating the surface of the mullite material with an aluminum-containing material before pretreating the surface of the mullite material using the plasma-chemical process.
12. A mullite material comprising an aluminum oxide-containing layer arranged on a surface of the mullite material, wherein spike-like structures with tips directed into the aluminum oxide-containing layer are formed in a boundary area between the mullite material and the aluminum oxide-containing layer wherein the spike-like structures have a width b between 50 nm and 200 nm and a height h of between 100 nm and 500 nm.
13. The mullite material according to claim 12 , wherein the spike-like structures comprise an aluminum oxide-containing material or consist of aluminum oxide.
14. The mullite material according to claim 12 , wherein a layer thickness of the aluminum oxide-containing layer is between 0.5 μm and 50 μm.
15. The mullite material according to claim 12 , wherein the aluminum oxide-containing layer is essentially single-phase.
16. The mullite material according to claim 12 , wherein the aluminum oxide-containing layer comprises metallic macroparticles.
17. The mullite material according to claim 12 , wherein the aluminum oxide-containing layer comprises at least one of the group consisting of chromium, titanium, hafnium, yttrium, erbium, silicon and zirconium.
18. A gas turbine component comprising the mullite material according to claim 12 .