A method for coating a composite structure, comprising applying a first slurry onto a surface of the composite structure, wherein the first slurry is a sol gel comprising a metal organic salt, a first carrier fluid, and a ceramic material, and heating the composite structure to a first sol gel temperature sufficient to form a sol gel-derived base layer on the composite structure.

A method may include applying a layer comprising a carbon source on a surface of a substrate including silicon; applying a layer comprising silicon on the layer comprising elemental carbon; and heat treating at least the layer comprising the carbon source to cause carbon from the layer comprising the carbon source to react with at least one of silicon from the substrate or silicon from the layer comprising silicon to form silicon carbide.

A coated fiber structure for use in a ceramic matrix composite comprises a fiber and a coating system applied to and circumscribing the fiber. The coating system comprises a first boron nitride layer, a silicon carbide layer extending coaxially with and in direct contact with the first boron nitride layer, a first thermally-grown oxide layer formed on the silicon carbide layer, and a second boron nitride layer extending coaxially with and in direct contact with the first thermally-grown oxide layer.

An oxidation protection system disposed on a substrate is provided, which may comprise a boron layer comprising a boron compound disposed on the substrate; a silicon layer comprising a silicon compound disposed on the boron layer; and at least one sealing layer comprising monoaluminum phosphate and phosphoric acid disposed on the silicon layer.

An oxidation protection system disposed on a substrate is provided, which may comprise a boron layer comprising a boron compound disposed on the substrate; a silicon layer comprising a silicon compound disposed on the boron layer; and at least one sealing layer comprising monoaluminum phosphate and phosphoric acid disposed on the silicon layer.

A surface-coated cutting tool including a substrate including a rake face and a flank face and a coating which covers a surface of the substrate is provided. The substrate is made of a cBN sintered material or a ceramic sintered material. The coating includes an alternating layer. The alternating layer is made by alternately stacking a first layer and a second layer different in composition from the first layer. The first layer contains Al, Cr, and N. The second layer contains Ti, Al, and N. A ratio T1/T2 between a thickness Ti of the first layer and a thickness T2 of the second layer is not lower than 0.1 and lower than 1. There are thirty or more interfaces at which the first layer and the second layer are in contact with each other.

A surface-coated cutting tool including a substrate including a rake face and a flank face and a coating which covers a surface of the substrate is provided. The substrate is made of a cBN sintered material or a ceramic sintered material. The coating includes an alternating layer. The alternating layer is made by alternately stacking a first layer and a second layer different in composition from the first layer. The first layer contains Al, Cr, and N. The second layer contains Ti, Al, and N. A ratio T1/T2 between a thickness Ti of the first layer and a thickness T2 of the second layer is not lower than 0.1 and lower than 1. There are thirty or more interfaces at which the first layer and the second layer are in contact with each other.

In some examples, a coating may include at least one feature that facilitates visual determination of a thickness of the coating. For example, the coating may include a plurality of microspheres disposed at a predetermined depth of the coating. The plurality of microspheres may define a distinct visual characteristic. By inspecting the coating and viewing at least one of the microspheres, the thickness of the coating may be estimated. In some examples, the plurality of microspheres may be embedded in a matrix material, and the distinct visual characteristic of the microspheres may be different than the visual characteristic of the matrix material. In other examples, the at least one feature may include at least one distinct layer in the coating system that includes a distinct visual characteristic, such as a color of the distinct layer.

In some examples, a coating may include at least one feature that facilitates visual determination of a thickness of the coating. For example, the coating may include a plurality of microspheres disposed at a predetermined depth of the coating. The plurality of microspheres may define a distinct visual characteristic. By inspecting the coating and viewing at least one of the microspheres, the thickness of the coating may be estimated. In some examples, the plurality of microspheres may be embedded in a matrix material, and the distinct visual characteristic of the microspheres may be different than the visual characteristic of the matrix material. In other examples, the at least one feature may include at least one distinct layer in the coating system that includes a distinct visual characteristic, such as a color of the distinct layer.

A method of depositing abradable coating on an engine component is provided wherein the engine component is formed of ceramic matrix composite and one or more layers, including at least one environmental barrier coating, may be disposed on the outer layer of the CMC. An outermost layer of the structure may further comprise a porous abradable layer that is disposed on the environmental barrier coating and provides a breakable structure which inhibits blade damage. The abradable layer may be gel-cast on the component and sintered or may be direct written by extrusion process and subsequently sintered.