SINTERING OF THE TOP COAT IN THERMAL SPRAY TBC SYSTEMS UNDER SERVICE CONDITIONS
J.A.Thompson, W.Ji, T. Klocker, T.W.Clyne
Department of Materials Science & Metallurgy Cambridge University
Abstract
Improved reliability of Thermal Barrier Coating (TBC) systems, under conditions in which the temperature at the free surface may be required to reach values as high as 1400C, is a critical aim for the next generation of gas turbine engines. It is now becoming clear that a significant contributory factor in the tendency for top coat spallation to occur in TBC systems during service is related to sintering effects in the zirconia top coat. There is already evidence(1) that the stiffness of detached top coats can rise substantially during heat treatments, even after relatively short periods at temperatures as low as about 1100-1200C. This increase in stiffness will lead to enhanced differential thermal contraction stresses during subsequent temperature changes and hence to an increase in the driving force for detachment of the coating(2). It seems likely that this phenomenon is at least partially responsible for many of the observed cases of debonding during service.
keywords:TBC; Thermal Barrier; bond coat; Zirconia; flow rate; top coats; THERMAL SPRAY; thermal gradient; Plasma Spraying; SLPM
|
