Methods for applying mitigation coatings, and related articles
A method for protecting a thermal barrier coating (TBC) which comprises voids is described. The method involves the step of electrophoretically depositing a mitigation coating material such as alumina to fill at least a portion of the voids. The TBC is often applied over a metal substrate, such as a turbine engine component. The voids can be in the form of vertical cracks within the TBC. A thermal barrier coating is also described, containing voids which extend into the coating from a top surface, wherein at least a portion of the voids is filled with a mitigation coating material.
1. A method for protecting a yttria-stabilized zirconia thermal barrier coating (TBC) which comprises voids from an environmental-contaminant material, comprising the steps of electrophoretically depositing a mitigation coating material to fill at least a portion of the voids in the yttria-stabilized zirconia thermal barrier coating, and contacting the thermal barrier coating with the environmental-contaminant material so that the mitigation coating material is capable of reacting with the contaminant material to raise the melting point of the contaminant material and/or increase its viscosity.
2. The method of claim 1 , wherein the voids comprise vertical cracks.
3. The method of claim 1 , wherein the mitigation coating material comprises metal oxide particles, metal hydroxide particles, or combinations thereof.
4. The method of claim 3 , wherein the mitigation coating is at least one material selected from the group consisting of single oxides and mixed oxides.
5. The method of claim 4 , wherein the single oxides are selected from the group consisting of alumina, magnesia, chromia, calcia, scandia, rare earth oxides, and combinations thereof.
6. The method of claim 4 , wherein the mixed oxides are selected from the group consisting of calcium zirconate, gadolinium zirconate, neodymium zirconate, alumino-silicates, spinels, and combinations thereof.
7. The method of claim 1 , wherein the environmental-contaminant material comprises calcium oxide, magnesium oxide, aluminum oxide, and silicon oxide.
8. The method of claim 1 , wherein the mitigation material is also deposited over the surface of the TBC, to form a surface coating.
9. The method of claim 1 , wherein the thermal barrier coating is disposed over a metal substrate.
10. The method of claim 9 , wherein the metal substrate is a turbine engine component.
11. The method of claim 9 , wherein the mitigation coating material is formed by placing the thermal barrier-coated substrate in a colloidal dispersion of coating material particles selected for the coating composition, and electrophoretically depositing the coating material to fill at least a portion of the voids.
12. The method of claim 11 , wherein the metal substrate is positioned in the colloidal dispersion so that the TBC surface openings to the voids are readily accessible to electrophoretic-induced movement of the mitigation coating material particles within the dispersion.
13. The method of claim 11 , wherein the coating material particles comprise alumina, and have an average particle size in the range of about 10 nm to about 1000 nm.