Erosion–corrosion behaviour of zirconia, WC–6Co, WC–6Ni and UNS S31600

Abstract

The current study investigates a ceramic, two sintered cermets and a metal under solid–liquid impingement with 3.5% NaCl and 150mg/l silica sand at two extreme angles of attack, 90° and 20°. The materials tested were zirconia ceramic, sintered WC–6Co, sintered WC–6Ni and UNS S31600. Each material was exposed to a testing regime using re-circulating impinging jet apparatus with a velocity of 19m/s over a test duration of 1h. The electrochemical properties of the materials were investigated in-situ through anodic and cathodic polarisations and application of cathodic protection (CP). Post experimental analysis of the degraded surface was completed using Scanning Electron Microscopy (SEM) and Optical 3D Imaging. At 90° angle of impingement, zirconia exhibited a brittle response to erosion–corrosion testing with the mass loss being fifty times greater than the negligible mass loss at 20° angle of impingement. WC–6Co and WC–6Ni both outperformed UNS S31600 under all solid–liquid impingement erosion–corrosion testing regimes. WC–6Ni exhibited slightly better erosion–corrosion resistance over WC–6Co at both 90° and 20°. UNS S31600 displayed the best corrosion resistance but its passive film was continuously damaged due to the presence of solid into the liquid solution. The nickel binder increased the corrosion resistance of WC–6Ni over WC–6Co. Cathodic protection was successfully applied on sintered WC–6Co and UNS S31600 isolating the key components of erosion–corrosion.