Accelerated corrosion behavior of a Stellite 6 alloy in a simulated marine atmospheric environment

This study systematically investigated the corrosion behaviour and degradation mechanisms of a Stellite 6 alloy in a simulated hot, humid marine atmosphere, using accelerated corrosion tests. The corrosion kinetics, passive film evolution and initiation of localised corrosion were evaluated. The results demonstrate that the corrosion mass loss of the alloy follows a power-function law, with the corrosion rate decreasing over exposure time. After approximately 300 hours of exposure, a dense passive film primarily composed of Cr 2 O 3 formed on the surface, significantly enhancing corrosion resistance. However, further exposure resulted in the localised breakdown of this passive film due to the combined action of Cl - and H + , leading to a shift from uniform to intergranular corrosion. Microstructural analysis confirmed the formation of micro-galvanic couples between M 23 C 6 carbides and adjacent chromium-depleted zones, which promoted preferential dissolution along grain boundaries. Scanning Kelvin probe potential mapping revealed micro-electrochemical heterogeneity and its temporal evolution. XPS analysis showed that the corrosion products contained oxides and hydroxides of Co, Cr and W, suggesting a potential synergistic effect between WO 3 and Cr 2 O 3 in enhancing passive film stability. This study provides valuable insights into the long-term performance of Co-Cr-W-based alloys in aggressive marine environments, offering guidance on the design and application of highly corrosion-resistant cobalt alloys.