CHARACTERISTICS OF HIGH TEMPERATURE VACUUM BRAZED WC-Co-NiCrBSi FUNCTIONAL COMPOSITE COATINGS

The present work aims to investigate the characteristics of high temperature vacuum brazed WC-Co-NiCrBSi coatings deposited on 16MnCr5 steel substrate. The coatings characteristics like morphology, microstructure, chemical composition and the appearance of the interface with the substrate have been analyzed by means of Scanning Electron Microscopy (SEM) combined with energy-dispersive X-ray spectroscopy. The hardness profile of the cladding is evaluated with the help of a Vickers microhardness tester. Size, occurrence and distribution of pores and microcracks has been estimated using image processing of SEM micrographs. X-ray diffraction measurements performed on the on the brazed composite cladding, have been done in order to identify possible phase transformations during the thermal treatment. Tribological behavior is assessed with the aid of a tribometer utilizing a pin-on-disk testing arrangement. Corrosion resistance is appraised using the potentiodynamic polarization method in 3.5% NaCl solution at room temperature in a three-electrode cell configuration. This coating technology makes possible the deposition of high quality hardfacings, with minimal influence on metallic substrate. The achieved porosity degree (approximately 1%) is similar to the values reported in literature. It was found that the mean coefficient of friction is approximately two times lower for the WC-Co-NiCrBSi composite, compared to 16MnCr5. Consequently, the wear rate of the coating is more than 20 times lower than that of the unprotected substrate material. The electrochemical measurements resulted in a lower corrosion current density, correlated with a significant improvement in the corrosion behavior.