CMAS Effects on Ship Gas-Turbine Components/Materials

Abstract

Recent inspection of shipboard gas-turbine components under the platform has indicated the apparent presence of CMAS (calcium, magnesium, alumino-silicate) and its related attack. This type of attack has often been observed in aero gas turbine engines when sand and similar siliceous matter is ingested into the engine and the sand debris melts due to high engine operating temperature greater than 1150°C. Initial chemical analysis shows that the CMAS-affected areas of ship engine components versus aero engine components are similar. However, this phenomenon commonly observed in advanced aeroengines are not supposed to occur in the ship engine components since their probable temperature is known to be much lower than 1150°C (i.e., melting temperature of CMAS). As a consequence, some important questions arise as to: What caused this “CMAS” attack in ship engine components? Was this initiated by hot corrosion, which created a molten salt pool at a sufficient temperature to trigger CMAS attack? Did sodium chloride mixed with dust and debris lower the temperature at which molten CMAS would initiate? Past research provides a basic understanding of hot corrosion, but may ignore other reactants and other species inherently associated with ‘natural CMAS’ and mechanisms contributing to hot corrosion or CMAS attack. Further examination of ship and aero components will discern the local structure chemical profile of the component coatings, the chemical compositions of the alloy substrates, and the interface between the coating and the molten “CMAS” by several methods. Integrated computational materials engineering (ICME) and validating experiments will assist in developing degradation mechanisms. The environment complexity is also to be taken into account to determine whether salt-induced CMAS attack or CaO-induced hot corrosion may be dominant. The mechanisms need to be further studied and defined. The current work will address a series of systematic approaches to the aforementioned CMAS issues and will also present some recent results on CMAS-related effects on components and an elected alloy material system.