The role of thermal properties in the wear mechanisms of an AlSi-polyester abradable

Abstract

During run-in and operation, the blades of a gas turbine engine may rub against the engine casing. To allow for these blade rubs an abradable coating is applied to the casing. However, the coating does not always cut smoothly, potentially wearing the blade. This paper focuses on the wear mechanics which occur with Metco 601, an AlSi-Polyester abradable which has been shown to produce a combination of blade wear and adhesion.

In this study, by testing AlSi-Polyester of different hardnesses at various incursion rates and blade speeds, it has been shown that there is a statistically significant difference in the wear behaviour observed at 0.02μm/pass compared with those observed between 0.2 and 2 μm/pass. Simultaneous recording of the blade front, thermal hotspots on the blade and abradable, and force measurements have been used to relate observed wear mechanics to the thermal behaviour of the abradable. Results showed that at incursion rates above 0.2μm/pass high force application rates lead to localised hotspots on the abradable and sporadic adhesion events. At 0.02μm/pass the force application rate, and hence thermal energy flux into the abradable, is more gradual, allowing heat to spread across the abradable surface. The more uniform abradable temperature leads to large areas of simultaneous wear, demonstrating how the abradables ability to manage the thermal energy can have a significant impact on its wear performance. This has been further verified through the observation of a reduction in abradable temperature as the test progresses which aligns with a reduction in the thermal resistance through the abradable and also an observed transition from adhesion to blade wear.

This work has shown that the management of thermal energy within AlSi-Polyester has a significant impact on the observed wear mechanisms, improving the understanding of why the wear mechanics vary with incursion rate.