Protective coating systems for gas turbine engine applications

A protective coating system comprising:

• a substrate formed of a ceramic matrix composite material, wherein the ceramic matrix composite material is a silicon carbide-silicon carbide (SiC-SiC) material, which includes a volume fraction of about 90% or more of SiC-based fibers;
• wherein the substrate has an exterior surface exhibiting a degree of valley/hill surface irregularity comprising a plurality of hills and a plurality of valleys;
• a first coating layer deposited from a sol-gel material, wherein the first coating layer is formed directly on to the exterior surface of the substrate and conforms to the exterior surface of the substrate such that the first coating layer has a non-uniform coating thickness over the substrate wherein the first coating layer has a thickness within the plurality of valleys that is greater than its thickness over the plurality of hills;
• a second, thermal barrier, porous coating layer formed directly on to the exterior surface of the first coating layer, wherein the second coating layer comprises a plurality of pores within the second coating layer, where the pores are at the surface and extending below the surface through various shapes and sizes;
• and
• a third coating layer partially formed directly on to an exterior surface of the second coating layer and partially formed within at least some of the plurality of pores within the second coating layer, wherein the third coating layer coats walls of at least some of the plurality of pores but does not completely fill the at least some of the plurality of pores,
• wherein:
• there is a porosity gradient within the second coating layer, and
• the porosity gradient is characterized by a relatively lesser degree of porosity adjacent to the exterior surface of the first coating layer and a relatively greater degree of porosity adjacent to the exterior surface of the second coating layer.