CMAS-resistant thermal barrier coating and method of making a coating thereof

1. A calcium-magnesium alumino-silicate (CMAS)-resistant coating system comprising:

an outer coating comprising:

a plurality of columnar structures denoted by a cauliflower-type surface topography and having a total porosity of less than five percent, wherein the columnar structures comprise:

a plurality of randomly-oriented particle splats; and

a CMAS-reactive material; and

a plurality of generally connected porosity bands forming vertically-oriented gaps extending from an outermost surface of the outer coating to a first depth of the outer coating equal to or less than a total thickness of the outer coating, wherein the connected porosity bands separate adjacent columnar structures by a median gap width less than five micrometers and wherein the connected porosity bands have a porosity less than 100 percent.

2. The CMAS-resistant coating system of claim 1 , wherein the median gap width of the plurality of vertically-oriented gaps is less than three micrometers.

3. The CMAS-resistant coating system of claim 1 , wherein the CMAS-reactive material comprises a rare earth element content ranging from 18 to 100 mole percent.

4. The CMAS-resistant coating system of claim 1 , wherein the CMAS-reactive material comprises gadolinia.

5. The CMAS-resistant coating system of claim 1 , wherein the columnar structures have a total porosity of less than three percent.

6. The CMAS-resistant coating system of claim 1 , wherein the outer coating has a total porosity of less than ten percent.

7. The CMAS-resistant coating system of claim 1 , wherein the outer coating has a total porosity of less than five percent.

8. The CMAS-resistant coating system of claim 1 , wherein an average distance between each of the plurality of vertically-oriented gaps ranges from 25-500 micrometers.

9. The CMAS-resistant coating system of claim 1 , wherein the plurality of vertically-oriented gaps are bands of connected porosity separating adjacent columnar structures.

10. The CMAS-resistant coating system of claim 9 , wherein the cracks extend from the outermost surface of the coating to a depth less than 60 percent of the outer coating thickness.

11. The CMAS-resistant coating system of claim 1 , and further comprising a plurality of vertically-oriented cracks.

12. The CMAS-resistant coating system of claim 1 , wherein an outermost portion of the plurality of vertically-oriented gaps is filled with a crystallization product of CMAS and the CMAS-reactive material, and wherein the plurality of vertically-oriented gaps are filled from the outermost surface of the outer coating to a second depth of the outer coating, wherein the second depth is less than the first depth.

13. The CMAS-resistant coating system of claim 12 , wherein the second depth is less than half of the total thickness of the outer coating.

14. The CMAS-resistant coating system of claim 1 , wherein at least 90 percent of the outer coating is free of generally horizontally-oriented gaps connecting adjacent vertically-oriented gaps.

15. The CMAS-resistant coating system of claim 1 and further comprising:

an inner coating comprising:

a plurality of columnar structures and

a material having a different chemical composition than the material of the outer coating.

16. A method of forming a calcium-magnesium alumino-silicate (CMAS)-resistant coating comprising:

providing a suspension feedstock comprising ceramic particles suspended in a liquid medium, wherein the ceramic particles comprises a CMAS-reactive material;

depositing the ceramic particles on the substrate to form an outer coating comprising a plurality of columnar structures having a total porosity of less than five percent, wherein the columnar structures are formed during material deposition and are denoted by a cauliflower-type surface topography and, wherein the columnar structures comprise:

a plurality of randomly-oriented particle splats; and

a CMAS-reactive material;

forming a plurality of generally connected porosity bands forming vertically-oriented gaps extending from an outermost surface of the outer coating to a first depth of the outer coating equal to or less than a total thickness of the outer coating, wherein the connected porosity bands are formed during material deposition and separate adjacent columnar structures by a median gap width of less than five micrometers and wherein the connected porosity bands have a porosity less than 100 percent.

17. The method of claim 16 , wherein the CMAS-reactive material comprises a rare earth element.

18. The method of claim 17 , wherein the CMAS-reactive material comprises gadolinia.

19. The method of claim 16 , wherein spraying the suspension feedstock comprises:

making multiple spray passes across the substrate to increase a total thickness of the coating in a layer-by-layer fashion; and

forming dense inter-pass regions of the coating such that at least 90 percent of the coating by volume is free of generally horizontally-oriented gaps connecting adjacent vertically-oriented gaps in the coating.

20. The method of claim 16 , and further comprising:

sealing a portion of the vertically-oriented gaps from ingress of molten CMAS, wherein sealing comprises filling a portion of the plurality of vertically-oriented gaps with a crystallization product of CMAS and the CMAS-reactive material, wherein the portion filled extends from an outermost surface of the coating.