Materials Solutions to Address High Temperature Fretting Wear in Gas Turbine Combustor Components

Structural parts like combustor and its components plays an important role in the overall performance of a land based heavy duty gas turbines. Due to system dynamics and poor material combinations, these parts undergo severe wear leading to durability issues and even part failures. Parts like liners, burners, transition piece and seals are free to undergo small amplitude motion and lead to fretting and related wear. In many situations, these component surfaces are un-coated or not protected from the severe degradation. The objective of this work is to develop a robust coating system to mitigate fretting and related wear under elevated temperature. A molybdenum rich-cobalt based tribaloy-800 is used to address the wear issues and studied in greater details. Tribaloy-800 multilayer coating is deposited on Nickel base alloy by HVOF coating process to achieve maximum distribution of laves hard phase. Further, coating is heat treated under vacuum furnace to optimize the microstructure which is desirable to work on these harsh operating conditions. A custom built fretting wear setup was used to perform gross-slip wear test, as standard laboratory experiments may not simulate the field wear mechanisms better. Both uncoated and coating materials were studied at elevated temperature (550 °C) under constant stress up to 3 million cycles to produce steady state wear rate. Fretting wear data reveals severe galling type of wear mechanisms in uncoated materials lead to fast removal material from the surface. Both as-coated and heat-treated coatings produced better wear resistance under same test conditions compared to uncoated nickel alloy. Heat treated tribaloy-800 coating shows crystalline rich laves phase distribution lead to superior wear performance.