Reactive thermal barrier coating
A calcium-magnesium-alumino-silicate (CMAS)-reactive thermal barrier coating includes a ceramic coating and a CMAS-reactive overlay coating, wherein the CMAS-reactive overlay coating conforms to a surface of the ceramic coating and comprises a compound that forms a stable high melting point crystalline precipitate when reacted with molten CMAS at a rate that is competitive with CMAS infiltration kinetics into the thermal barrier coating. The ceramic coating phase is stable with the CMAS-reactive overlay coating.
1. A calcium-magnesium-alumino-silicate (CMAS)-reactive thermal barrier coating comprising:
a ceramic coating comprising a plurality of featherlike columnar grains separated by vertically-oriented gaps open to an outer surface, wherein the ceramic coating comprises a fully stabilized zirconate or hafnate structure; and
a CMAS-reactive overlay coating forming a conformal layer with uniform surface coverage on surfaces of the featherlike grains extending into the vertically-oriented gaps, wherein the vertically-oriented gaps remain open to the outer surface, and wherein the CMAS-reactive overlay coating comprises a compound selected from a group consisting of a pure rare earth oxide and a mixed rare earth oxide that forms a crystalline precipitate when reacted with molten CMAS at a rate substantially equal to or greater than a rate at which the molten CMAS infiltrates through the thermal barrier coating;
wherein the ceramic coating is phase stable with the CMAS-reactive overlay coating.
2. The CMAS-reactive thermal barrier coating of claim 1 , wherein the ceramic coating comprises gadolinium zirconate.
3. The CMAS-reactive thermal barrier coating of claim 1 , wherein the ceramic coating comprises yttrium zirconate.
4. The CMAS-reactive thermal barrier coating of claim 1 , wherein the CMAS-reactive overlay is deposited in pores open to the vertically-oriented gaps.
5. The CMAS-reactive thermal barrier coating of claim 4 , wherein the thickness of the CMAS-reactive overlay ranges from 10 to 500 nanometers.
6. The CMAS-reactive thermal barrier coating of claim 4 , wherein the CMAS-reactive overlay extends into the vertically-oriented gaps to a depth of at least one-third of a thickness of the ceramic coating from the outer surface of the ceramic coating.
7. The CMAS-reactive thermal barrier coating of claim 6 , wherein the CMAS-reactive overlay extends into the vertically-oriented gaps to a depth of at least one-half of a thickness of the ceramic coating from an outer surface of the ceramic coating.
8. The CMAS-reactive thermal barrier coating of claim 1 , wherein the CMAS-reactive overlay has a material composition that will react with molten CMAS to form an oxy-apatite phase.