Improvement of corrosion performance of HVOF MMC coatings by laser surface treatment

Abstract

In order to improve corrosion performance of T800 (Co–Mo–Cr–Si) and T800 based WC HVOF sprayed coatings, laser surface modification was carried out using a high power diode laser to eliminate/reduce the microstructral defects of the coatings by precise control of treatment depth with or without melting. Characterisation of the laser modified surfaces was conducted, in terms of microstructural morphology and phase analysis. Corrosion behaviours of the coatings before and after laser treatment were evaluated using electrochemical impedance spectroscopy and immersion tests. The results indicated that the corrosion resistance of the HVOF coatings can be improved as a result of laser densification of the coatings by elimination of discrete splat structure and porosity. However, the improvement of resistance to microgalvanic corrosion between the WC and Co matrix after laser treatment can be limited depending on the extent of melting occurred to the WC within the coatings.