CMAS-resistant barrier coatings
A method includes predicting a composition of calcium-magnesium-aluminum-silicate (CMAS) to be encountered by a high temperature mechanical system during use of the high temperature mechanical system. The method further includes selecting a composition of a CMAS-resistant barrier coating layer based at least in part on the predicted composition of CMAS. The CMAS-resistant barrier coating layer includes a base composition and at least one secondary oxide selected based on the predicted composition of CMAS. The at least one secondary oxide includes at least one of an oxide of a divalent element, an oxide of a trivalent element, or an oxide of a tetravalent element. The CMAS-resistant barrier coating layer comprises greater than 0 mol. % and less than about 7 mol. % of the at least one secondary oxide.
1. A method comprising:
predicting a composition of active components of calcium-magnesium-aluminum-silicate (CMAS) to be encountered by a high temperature mechanical system during use of the high temperature mechanical system, wherein the composition of active components of CMAS comprises a relative molar composition of at least two of calcium oxide, magnesium oxide, aluminum oxide, or silicon oxide; and
selecting a composition of a CMAS-resistant barrier coating layer based at least in part on the predicted composition of active components of CMAS, wherein, prior to exposure of the barrier coating to an operating environment of the high temperature mechanical system, the CMAS-resistant barrier coating layer comprises:
a base composition comprising at least one of a rare earth monosilicate or a rare earth disilicate;
at least one secondary oxide selected based on the predicted composition of active components of CMAS to reduce, compared to the base composition alone, at least one of:
a diffusion gradient of the active components of CMAS into the CMAS-resistant barrier coating layer; or
a reaction gradient of the active components of CMAS with the base composition of the CMAS-resistant barrier coating layer,
wherein the at least one secondary oxide comprises at least one of an oxide of a divalent element, an oxide of a trivalent element, or an oxide of a tetravalent element,
wherein the CMAS-resistant barrier coating layer comprises greater than 0 mol. % and less than about 7 mol. % of the at least one secondary oxide, and
wherein the at least one secondary oxide includes at least one of calcium oxide, barium oxide, magnesium oxide, aluminum oxide, or silicon oxide.
2. The method of claim 1 , wherein predicting the composition of active components of CMAS to be encountered comprises predicting a basicity index of CMAS, wherein the basicity index is represented by the equation:
Basicity
Index
=
Σ
mol
.
%
Basic
Oxides
Σ
mol
.
%
Acidic
Oxides
where the basic oxides include at least calcium oxide and the acidic oxides include at least silicon dioxide.
3. The method of claim 2 , wherein the predicted basicity index is less than about 2, and wherein the at least one secondary oxide comprises at least one oxide of a divalent element.
4. The method of claim 3 , wherein the CMAS-resistant barrier coating layer is acidic.
5. The method of claim 2 , wherein the predicted basicity index is greater than about 2, and wherein the at least one secondary oxide comprises at least one oxide of a tetravalent element.
6. The method of claim 5 , wherein the CMAS-resistant barrier coating layer is basic.
7. The method of claim 2 , wherein the predicted basicity index is between about 1.8 and about 2.2, and wherein the at least one secondary oxide comprises at least one oxide of a divalent element and at least one oxide of a tetravalent element.
8. The method of claim 1 , wherein the CMAS-resistant barrier coating layer comprises an environmental barrier coating (EBC) layer.
9. The method of claim 1 , further comprising forming the CMAS-resistant barrier coating layer over a substrate of the high temperature mechanical system using at least one of plasma spraying, electron beam physical vapor deposition, plasma sprayed physical vapor deposition, suspension plasma spraying, or direct vapor deposition.
10. The method of claim 9 , further comprising forming a bond layer on the substrate, and wherein forming the CMAS-resistant barrier coating layer over the substrate comprises forming the CMAS-resistant barrier coating layer over the bond layer.
11. The method of claim 10 , further comprising forming a second barrier coating layer over the substrate, and wherein forming the CMAS-resistant barrier coating layer over the substrate comprises forming the CMAS-resistant barrier coating layer over the second barrier coating layer.
12. The method of claim 1 , wherein the CMAS-resistant barrier coating layer comprises a thickness between about 1 mil and about 20 mils.
13. The method of claim 1 , wherein predicting the composition of active components of CMAS to be encountered comprises referencing CMAS composition information based on an intended geographical location of operation.