CMAS-resistant abradable coatings
In some examples, an article includes a ceramic or a ceramic or ceramic matrix composite (CMC) substrate; and an abradable coating on the CMC substrate. The abradable coating includes a plurality of first rare earth (RE) silicate layers in an alternating arrangement with a plurality of second RE silicate layers, wherein the first RE silicate layers include a rare earth monosilicate and the second RE silicate layers include a rare earth disilicate, and wherein the first RE silicate layers include a greater concentration of the rare earth monosilicate than the second RE silicate layers.
1. A system comprising:
a ceramic or ceramic matrix composite (CMC) substrate;
an abradable coating on the CMC substrate, the abradable coating comprising a plurality of first rare earth (RE) silicate layers in an alternating layer arrangement with a plurality of second RE silicate layers such that the abradable coating includes a first layer, a second layer, a third layer, a fourth layer, and a fifth layer, in that order, on the ceramic or the CMC substrate with the fifth layer being located between the fourth layer and the ceramic or the CMC substrate,
wherein the plurality of first RE silicate layers includes the first layer, the third layer, and the fifth layer,
wherein the plurality of second RE silicate layers includes the second layer and the fourth layer,
wherein the first RE silicate layers include a rare earth monosilicate and the second RE silicate layers include a rare earth disilicate, and wherein the first RE silicate layers include a greater concentration of the rare earth monosilicate than the second RE silicate layers; and
an opposing abrasive element configured to abrade the abradable coating to a maximum penetration depth such that at least the first layer and the third layer of the plurality of first RE silicate layers and at least the second layer and the fourth layer of the plurality of second RE silicate layers are abraded by the opposing abrasive element, and the fifth layer of the plurality of first RE silicate layers is between the substrate and the maximum penetration depth such that the fifth layer of the plurality of first RE silicate layers defines a continuous and undisturbed CMAS resistant barrier layer over the CMC substrate after the opposing abrasive element abrades to the maximum penetration depth,
wherein the first layer, the third layer, and the fifth layer of the plurality of first RE silicate layers each include at least about 20 wt. % rare earth monosilicate, and wherein the second layer and the fourth layer of the plurality of second RE silicate layers each include at least about 50 wt. % of the rare earth disilicate,
wherein a thickness of each of the first layer, the third layer, and the fifth layer is less than a thickness of each of the second layer and the fourth layer, and
wherein a porosity of each of the second layer and the fourth layer is greater than a porosity of each of the first layer, the third layer, and the fifth layer.
2. The system of claim 1 , wherein the first RE silicate layers, including the first layer, third layer, and fifth layer, includes the rare earth monosilicate with a remainder being the rare earth disilicate.
3. The system of claim 1 , wherein the alternating arrangement of the first RE silicate layers and the second RE silicate layers comprises about 5 to about 100 layers.
4. The system of claim 1 , wherein a total thickness of the abradable coating is between about 250 micrometers and about 2500 micrometers.
5. The system of claim 1 , wherein the rare earth disilicate comprises ytterbium disilicate (YbDS), and the rare earth monosilicate comprises ytterbium monosilicate (YbMS).
6. The system of claim 5 , wherein the first RE silicate layers, including the first layer, third layer, and fifth layer, comprise at least about 20 wt % of YbMS and the second RE silicate layers comprise at least about 50 wt % of YbDS.
7. The system of claim 6 , wherein the second RE silicate layers, including the second layer and fourth layer, consists essentially of YbDS.
8. The system of claim 6 , wherein the second RE silicate layers, including the second layer and fourth layer, includes at least about 50 wt % of YbDS and a remainder of YbMS.
9. The system of claim 1 , further comprising a bond coat on at least a portion of the substrate, wherein the abradable coating is on the bond coat.
10. The system of claim 9 , wherein the bond coat comprises Si.
11. The system of claim 9 , further comprising an environmental barrier coating (EBC) between the bond coat and the abradable coating.
12. The system of claim 11 , wherein the EBC is a hermetic EBC comprising the rare earth disilicate and the rare earth monosilicate.
13. The system of claim 1 , wherein the abradable coating includes an outer layer defining an outer surface of the abradable coating, wherein the outer layer is the first layer of the plurality of first RE silicate layers.
14. The system of claim 1 , wherein the plurality of first rare earth (RE) silicate layers in the alternating arrangement with the plurality of second RE silicate layers reduces thermal stress on the abradable coating compared to a similar abradable coating having a similar amount of material but having only a one or two layer structure.
15. The system of claim 1 , wherein the plurality of first rare earth (RE) silicate layers in the alternating arrangement with the plurality of second RE silicate layers reduces crack propagation through the abradable coating compared to a similar abradable coating having a similar amount of material but having only a one layer structure.
16. The system of claim 1 , wherein the thickness of each of the second layer and the fourth layer is at least twice the thickness of each of the first layer, the third layer, and the fifth layer.
17. The system of claim 1 , wherein the first layer is directly on the second layer, wherein the second layer is directly on the third layer, and wherein the third layer is directly on the fourth layer.
18. The system of claim 1 , wherein the porosity of each of the first layer, the third layer, and the fifth layer is about 5 percent or less, and wherein the porosity of each of the second layer and the fourth layer is about 10 percent or greater.
19. A system comprising:
a ceramic or ceramic matrix composite (CMC) substrate;
an abradable coating on the CMC substrate, the abradable coating comprising a plurality of first rare earth (RE) silicate layers in an alternating layer arrangement with a plurality of second RE silicate layers such that the abradable coating includes a first layer, a second layer, a third layer, a fourth layer, and a fifth layer, in that order, on the ceramic or the CMC substrate with the fifth layer being located between the fourth layer and the ceramic or the CMC substrate,
wherein the plurality of first RE silicate layers includes the first layer, the third layer, and the fifth layer,
wherein the plurality of second RE silicate layers includes the second layer and the fourth layer,
wherein the first RE silicate layers include a rare earth monosilicate and the second RE silicate layers include a rare earth disilicate, and wherein the first RE silicate layers include a greater concentration of the rare earth monosilicate than the second RE silicate layers; and
an opposing abrasive element configured to abrade the abradable coating to a maximum penetration depth such that at least the first layer and the third layer of the plurality of first RE silicate layers and at least the second layer and the fourth layer of the plurality of second RE silicate layers are abraded by the opposing abrasive element, and the fifth layer of the plurality of first RE silicate layers is between the substrate and the maximum penetration depth such that the fifth layer of the plurality of first RE silicate layers defines a continuous and undisturbed CMAS resistant barrier layer over the CMC substrate after the opposing abrasive element abrades to the maximum penetration depth,
wherein the first layer, the third layer, and the fifth layer of the plurality of first RE silicate layers each include at least about 20 wt. % rare earth monosilicate, and wherein the second layer and the fourth layer of the plurality of second RE silicate layers each include at least about 50 wt. % of the rare earth disilicate,
wherein a thickness of each of the first layer, the third layer, and the fifth layer is less than a thickness of each of the second layer and the fourth layer,
wherein a porosity of each of the second layer and the fourth layer is greater than a porosity of each of the first layer, the third layer, and the fifth layer,
wherein the plurality of first rare earth (RE) silicate layers in the alternating arrangement with the plurality of second RE silicate layers reduces thermal stress on the abradable coating compared to a similar abradable coating having a similar amount of material but having only a one or two layer structure, and
wherein the plurality of first rare earth (RE) silicate layers in the alternating arrangement with the plurality of second RE silicate layers reduces crack propagation through the abradable coating compared to a similar abradable coating having a similar amount of material but having only a one layer structure.
20. A method comprising:
forming an abradable coating on a ceramic or CMC substrate, the abradable coating comprising a plurality of first rare earth (RE) silicate layers in an alternating layer arrangement with a plurality of second RE silicate layers such that the abradable coating includes a first layer, a second layer, a third layer, a fourth layer, and a fifth layer, in that order, on the ceramic or the CMC substrate with the fifth layer being located between the fourth layer and the ceramic or the CMC substrate,
wherein the plurality of first RE silicate layers includes the first layer, the third layer, and the fifth layer,
wherein the plurality of second RE silicate layers includes the second layer and the fourth layer,
wherein the first RE silicate layers include a rare earth monosilicate and the second RE silicate layers include a rare earth disilicate, and wherein the first RE silicate layers include a greater concentration of the rare earth monosilicate than the second RE silicate layers; and
abrading, via an opposing abrasive element, the abradable coating to a maximum penetration depth such that least the first layer and the third layer of the plurality of first RE silicate layers and at least the second layer and the fourth layer of the plurality of second RE silicate layers are abraded by the opposing abrasive element, and the fifth layer of the plurality of first RE silicate layers is between the substrate and the maximum penetration depth such that the fifth layer of the plurality of first RE silicate layers defines a continuous and undisturbed CMAS resistant barrier layer over the CMC substrate after the opposing abrasive element abrades to the maximum penetration depth,
wherein the first layer, the third layer, and the fifth layer of the plurality of first RE silicate layers each include at least about 20 wt. % rare earth monosilicate, and wherein the second layer and the fourth layer of the plurality of second RE silicate layers each include at least about 50 wt. % of the rare earth disilicate,
wherein a thickness of each of the first layer, the third layer, and the fifth layer is less than a thickness of each of the second layer and the fourth layer, and
wherein a porosity of each of the second layer and the fourth layer is greater than a porosity of each of the first layer, the third layer, and the fifth layer.