THE CVD OF REFRACTORY CARBIDES

Thermal Expansion Matching. The coefficients of thermal expansion (CTE) of coating and substrate should match as closely as possible. The CTE of the coating is usually lower than that of a metallic substrate and, upon cooling from the deposition temperature, thermal stresses are produced which may cause cracks and delamination. Such considerations have led to the development of low-temperature deposition processes such plasma-CVD or metallo-organic CVD (MOCVD) which minimizes these stresses and reduces the chance of coating failure (see Sec. 3.1).P1 

Low Deposition Pressure. In any CVD reaction, when the partial pressure of the reactants and carrier gases is low, the boundary layer becomes thinner and, as a result, the diffusion of the reactants through this layer is increased.1 1 The mass transfer variables become less critical and a more uniform coating is obtained. This is an important fector especially if many components are to be coated in one operation. Such low pressure CVD is the most common CVD process for the deposition of refractory carbides and nitrides. 

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