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Abstract

A NbSi.sub.2-base nanocomposite coating formed on the surface of niobium or niobium-base alloys is disclosed. The nanocomposite coating layer is manufactured by forming a niobium carbide layers or a niobium nitride layers by depositing of carbon or nitrogen on the surface, and then depositing silicon. The nanocomposite coating layer has a microstructure that SiC or Si.sub.3N.sub.4 particles are mostly precipitated on an equiaxed NbSi.sub.2 grain boundary. The thermal expansion coefficients of NbSi.sub.2-base nanocomposite coating layers become close to that of the substrates by adjusting the volume fraction of SiC or Si.sub.3N.sub.4 particles in the nanocomposite coating layers. Accordingly, the generation of cracks caused by thermal stress due to the mismatch in thermal expansion coefficient between the NbSi.sub.2-base nanocomposite coatings and the substrates can be suppressed, thereby improving the high-temperature oxidation resistance in the repeated thermal cycling use of the NbSi.sub.2-base nanocomposite coated substrates. Further, the increase in the volume fraction of dense SiO.sub.2 oxide phase formed on the surface of the NbSi.sub.2-base nanocomposite coating layers improves also high-temperature isothermal oxidation resistance.

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First Claim