Mechanisms and Kinetics of WC-Co-Cr High Velocity Oxy-Fuel Thermal Spray Coating Degradation in Corrosive Environments

Abstract

In this work, aspects of the corrosion behavior of WC-Co−Cr high velocity oxy-fuel (HVOF) thermal spray coatings have been assessed using a combination of x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to understand the corrosion mechanisms and, in particular, the electrochemical interactions between phases. Direct curent electrochemical accelerated corrosion techniques (potentiodynamic and potentiostatic tests) were performed to evaluate the corrosion kinetics of the coating. After the corrosion tests, the solution was analyzed using the inductively coupled plasma (ICP) technique, and a considerable amount of dissolved tungsten was detected. By combining information from XPS, SEM, ICP, and anodic polarization results, it is possible to propose a number of key reactions that can take place during WC-Co−Cr coating degradation, thus enabling the susceptible components of the coating to be identified. The implications of these findings for coating durability are discussed.