Thermal barrier coating protected by thermally glazed layer and method for preparing same
A thermal barrier coating for an underlying metal substrate of articles that operate at, or are exposed to, high temperatures, as well as being exposed to environmental contaminant compositions. This coating comprises an inner layer nearest to the underlying metal substrate comprising a ceramic thermal barrier coating material having a melting point of at least about 2000° F. (1093° C.), as well as a thermally glazed outer layer having an exposed surface and a thickness up to 0.4 mils (about 10 microns) and sufficient to at least partially protect the thermal barrier coating against environmental contaminants that become deposited on the exposed surface, and comprising a thermally glazeable coating material having a melting point of at least about 2000° F. (1093° C.) in an amount up to 100%. This coating can be used to provide a thermally protected article having a metal substrate and optionally a bond coated layer adjacent to and overlaying the metal substrate. The thermal barrier coating can be prepared by forming the inner layer comprising the ceramic thermal barrier coating material, followed by depositing the thermally glazeable coating material on the inner layer, and then thermally melting the thermally glazeable coating material to form the thermally glazed outer layer.
1. A method for preparing a thermal barrier coating for an underlying metal substrate, the method comprising the steps of:
1. forming an inner layer overlaying the metal substrate, the inner layer comprising a ceramic thermal barrier coating material having a melting point of at least about 2000° F.
2. depositing on the inner layer a thermally glazable coating material having a melting point of at least about 2000° F.; and
3. thermally melting by laser beam the deposited thermally glazeable coating material so as to form a thermally laser glazed outer layer adjacent to and overlaying the inner layer and having exposed surface, the thermally glazed outer layer having a thickness up to about 0.4 mils and sufficient to at least partially protect the thermal barrier coating against environmental contaminants that become deposited on the exposed surface.
2. The method of claim 1 wherein a bond coat layer is adjacent to and overlies the metal substrate and wherein the inner layer is formed on the bond coat layer.
3. The method of claim 2 wherein step (2) comprises depositing on the inner layer a mixture of from about 50 to about 95% of a chemically-stabilized zirconia, and from about 5 to about 50% alumina.
4. The method of claim 2 wherein step (2) comprises depositing on the inner layer a mixture of from about 80 to about 90% of a yttria-stabilized zirconia, and from about 10 to about 20% alumina.
5. A thermal barrier coating for an underlying metal substrate, which comprises:
a. an inner layer nearest to and overlaying the metal substrate and comprising from about 95 to 100% of a zirconia; and
b. a thermally glazed outer layer adjacent to and overlaying the inner layer and having an exposed surface, the outer layer having a thickness up to about 0.4 mils and sufficient to at least partially protect the thermal barrier coating against environmental contaminants that become deposited on the exposed surface, the outer layer comprising from about 95 to 100% of a thermally glazeable mixture comprising from about 50 to about 95% chemically-stabilized zirconia, and from about 5 to about 50% alumina.
6. The coating of claim 5 which has a thickness of from about 1 to about 100 mils and wherein the outer layer has a thickness in the range of from 0.04 to about 0.4 mils.
7. The coating of claim 6 wherein the outer layer has a thickness in the range of from about 0.1 to about 0.4 mils.
8. The coating of claim 5 wherein the outer layer is thermally laser glazed.
9. The coating of claim 5 wherein the inner layer comprises from about 98 to 100% of a yttria-stabilized zirconia and wherein the outer layer comprises from about 98 to 100% of mixture of from about 80 to about 90% a yttria-stabilized zirconia, and from about 10 to about 20% alumina.
10. A thermally protected article, which comprises:
1. a metal substrate; and
2. a bond coat layer adjacent to and overlaying the metal substrate;
3. a thermal barrier coating having a thickness of from about 1 to about 100 mils and comprising:
a. an inner layer adjacent to and overlaying the bond coat layer and comprising from about 95 to 100% zirconia; and
b. a thermally laser glazed outer layer adjacent to and overlaying the inner layer and having an exposed surface, a thickness of from about 0.1 to about 0.4 mils, and comprising from about 95 to 100% of mixture of from about 50 to about 95% of a chemically-stabilized zirconia, and from about 5 to about 50% alumina.
11 .The article of claim 10 wherein the inner layer comprises from about 98 to 100% of a yttria-stabilized zirconia and wherein the outer layer comprises from about 98 to 100% of mixture of from about 80 to about 90% of a yttria-stabilized zirconia, and from about 10 to about 20% alumina.
12. The article of claim 10 which is a turbine engine component.
13. The component of claim 12 which is a turbine shroud and wherein the thermal barrier coating has a thickness of from about 30 to about 70 mils.
14. The shroud of claim 13 wherein the thermal barrier coating has a thickness of from about 40 to about 60 mils.