Galvanic corrosion resistant coating composition and methods for forming the same
Coating systems for components of a gas turbine engine, such as a compressor case, are provided. The coating system can include a dense layer disposed along the inner surface of the compressor case as well as an abradable, top coat disposed along the dense layer. The combination of dense layer and abradable top coat can reduce the occurrence of galvanic corrosion of the coating system and thereby increase the lifetime of the coating system and preserve blade clearances within the compressor. Methods are also provided for applying the coating system onto a compressor case.
1. A gas turbine engine comprising:
a compressor comprising a compressor case having an inner surface, wherein the compressor case comprises a base material, wherein the base material comprises titanium; and
a coating system disposed over the inner surface of the compressor case, wherein the coating system comprises:
a bond coat over the inner surface of the compressor case, wherein the bond coat comprises nickel aluminum;
a dense layer comprising a dense layer material over the bond coat, wherein the dense layer material comprises aluminum silicon, wherein the dense layer has an average thickness of from 1 mil to 8 mils; and
an abradable top coat comprising an abradable top coat material over the dense layer, wherein the abradable top layer material comprises aluminum silicon, and wherein the dense layer has a higher density than the abradable top coat, and further wherein the dense layer and the abradable top layer have no substantial difference in galvanic potential.
2. The gas turbine engine according to claim 1 , wherein the dense layer has a density of 2 kg/m 3 to 2.7 kg/m 3 .
3. The gas turbine engine according to claim 1 , wherein the density of the dense layer is 20% to 270% greater than the density of the abradable top layer.
4. The gas turbine engine according to claim 1 , wherein the density of the dense layer is 30% to 250% greater than the density of the abradable top layer.
5. The gas turbine engine according to claim 1 , wherein the coating system has a tensile strength of 4000 psi to 6200 psi.
6. The gas turbine engine according to claim 1 , wherein the coating system has a tensile strength of 4800 psi to 5200 psi.
7. The gas turbine engine according to claim 1 , wherein the gas turbine engine is a turboshaft engine.
8. The gas turbine engine according to claim 1 , wherein the dense layer material and the abradable top layer material comprise the same chemical composition.
9. The gas turbine engine according to claim 1 , wherein the dense layer material and the abradable top layer material comprise different chemical compositions.
10. A method of preparing a coated compressor case of a gas turbine engine, the method comprising:
forming a bond coat over an inner surface of a base material of a compressor case, wherein the base material comprises titanium, and wherein the bond coat comprises nickel aluminum;
forming a dense layer over the bond coat, wherein the dense layer comprises a dense layer material, wherein the dense layer material comprises aluminum silicon, wherein the dense layer has an average thickness of from 1 mil to 8 mils; and
forming an abradable top coat over a surface of the dense layer, wherein the abradable top coat comprises an abradable top coat material, wherein the abradable top layer material comprises aluminum silicon, and wherein the dense layer has a higher density than the abradable top coat.
11. The method according to claim 10 , wherein forming the dense layer comprises thermally spraying aluminum silicon with argon gas as a carrier gas.
12. The method according to claim 10 , wherein forming the dense layer comprises thermally spraying aluminum silicon with argon gas as a carrier gas and with a plasma current of 600 Amps.
13. The method according to claim 12 , further comprising applying hydrogen gas as a secondary carrier gas.
14. The method according to claim 10 , wherein forming the top coat comprises thermally spraying aluminum silicon with nitrogen gas as a carrier gas and with a plasma current of 275 Amps.