Patent ID: 7978402

Claim:
An article comprising: a substrate; and a composite coating disposed over the substrate and extending from an interface with the substrate to an external surface, the composite coating comprising a first phase and a second phase, the second phase having a higher resistance to erosive wear than the first phase; wherein the coating comprises a compositional gradient proceeding from a first composition at the interface of the coating with the substrate to a second composition at the external surface, the first composition comprising a higher concentration of the first phase than that of the second composition; wherein the first phase has at least one property selected from the group consisting of a) a coefficient of thermal expansion (CTE) that is within about plus or minus 3 parts per million per degree centigrade of a CTE of the substrate, and b) an index of refraction that is within a range from as high as about 0.1 plus the index of refraction of the substrate to as low as about the square root of the index of refraction of the substrate; wherein the coating and the substrate are capable of transmitting infrared radiation.