Characterisation of CVD Niobium Carbide Coatings on Hard Carbide Substrate

Résumé

Hard coatings are often used for mechanical properties such as wear and friction resistance. The corrosion behaviour may also be an important criterion for industrial applications of these coatings. In this paper, the protective behaviour of niobium carbide coatings onto hard carbide substrate was investigated in 3% NaCl and 1M H₂SO₄ solutions. The corrosion behaviour of the carbide coatings depends not only on the intrinsic electrochemical properties of the coatings, but depends also by the surface defects such as roughness, deposited droplets during CVD process and mainly by pinholes, cracks and scratches. The experiments conducted to obtain thin layer of carbide through the vapour chemical deposition method have followed an original path to obtain NbC directly in the working room thus avoiding the import of these hazardous substances.
Characterisation of coating deposed by CVD method was done using scanning electron microscope (SEM), X-ray diffractometer (XRD) and Knoop hardness. Scanning Electron Microscope was used to investigate the coating morphology and interface structure. X-ray mapping were also performed to characterise the elements in a semi-quantitative analysis. Dron X-ray diffractometer with Mo K_α radiation operating was used for phase(s) identification. Microhardness value (Knoop hardness) measured in the coating layer was 30.000 MPa.