Structural, mechanical and electrical-contact properties of nanocrystalline-NbC/amorphous-C coatings deposited by magnetron sputtering

Niobium-carbide nanocomposite coatings with a carbon content varying from 43 to 64at.% were deposited by dual DC magnetron sputtering. X-ray diffraction, x-ray photoelectron spectroscopy and electron microscopy showed that all coatings consisted of nanometer sized NbC grains embedded in a matrix of amorphous carbon. Mechanical properties and electrical resistivity showed a strong dependency on the amount of amorphous carbon (a-C) and NbC grain size in the coating. The highest hardness (23GPa), elastic modulus (295GPa) and the lowest resistivity (260μΩcm) were measured for the coating with about 15% of a-C phase. Contact resistance measurements using a crossed cylinder set-up showed lowest contact resistance for the coating containing 33% a-C (140μΩ at a contact force of 100N), which is comparable to a Ag reference (45μΩ at a contact force of 100N). Comparison with TiC-based nanocomposites studied under similar conditions showed that the NbC system has less tendency to form a-C and that lowest contact resistance is obtained at comparable amounts of a-C phase in both material systems (33% for NbC compared to 35% for TiC). With these good electrical contact properties, the NbC nanocomposites can be considered as a potential material for electrical contact applications. ► The microstructure in the nc-NbC/a-C coatings depends strongly on the carbon content. ► Coating properties are strongly dependent on the amount of amorphous carbon. ► Lowest contact resistance is found for the coating containing 38% of a-C phase. ► nc-NbC/a-C is a potential material for electrical contact applications.