High temperature coatings

A method, comprising:

• forming a crystallized metal carbide undercoat on a surface of a carbon-carbon composite substrate;
• and
• forming an overcoat on a surface of the crystallized metal carbide undercoat,
• wherein the overcoat comprises a plurality of crystallized ultra-high melting point overcoat layers,
• wherein at least two overcoat layers of the plurality of overcoat layers have at least one of a different coefficient of thermal expansion, thermal conductivity, porosity, or thermal stability,
• wherein each overcoat layer is sequentially formed on an underlying layer by at least:
• applying a mixture to a surface of the underlying layer, wherein the mixture comprises a plurality of ultra-high melting point refractory ceramic particles and a pre-ceramic polymer, wherein the ultra-high melting point refractory ceramic particles have a melting point of at least about 2400° C.;
• and
• prior to applying a mixture for a subsequent layer, heating, in an inert atmosphere or under vacuum, the mixture to a heat treatment temperature to pyrolyze the pre-ceramic polymer and form the overcoat layer,
• wherein each overcoat layer comprises a crystallized ultra-high melting point polymer-derived ceramic matrix that includes the plurality of ultra-high melting point refractory ceramic particles, and
• wherein an outermost layer of the overcoat comprises an outermost overcoat layer of the plurality of overcoat layers.