Plasma-Sprayed ceramic coatings are an appealing alternative to shrouded vane interstage labyrinth seals, as they offer a simpler architecture and a significant drop in aero-engine’s weight. Historically, aero-engine sizes have not allowed manufacturers to mount vanes in cantilever. Due to their length, stresses have had to be diminish by securing their inner ends to a shroud; then using an abradable lining to limit gas recirculation around the stator. Currently, engine sizes have decreased, allowing to improve the weight penalties introduced by this design by removing the shroud and directly applying an abrasive lining on the rotating drum, with sealing achieved by the liner on the drum wearing the stator blades. Whilst abradable based sealing systems where the blade cuts the liner are well researched, little work has been undertaken on abrasive systems where the static blade is now worn.
The initial focus of this research has been to develop a high-speed rig and a monitoring system that allows the evaluation of different contact scenarios under more representative
in-service conditions. The gathered data, during and post-test, has served to identify metrics that describe the tribological system and holds the opportunity to link aero-engine conditions
with the ceramic lining performance. Cutting speed, incursion rate, ceramic material, abrasive surface finish, and coatings’ porosity have been identified as system variables, and a statistically planned test matrix has allowed to identify the significance and dependencies of each, along with building the required knowledge to optimise the tribological system.
The wear mechanism was defined as rubbing, with it exhibiting a progressive and thermally driven adhesion. Zirconia’s outcome was dragged down by its low conductivity, whilst alumina
was found to delaminate. Extending the arc of contact and triggering surface renewal were seen to delay the progressive process. Further investigation with added porosity (e.g. through
polyester) showed that the coating’s microstructure can be tuned for the applied stresses, and when self-renew the outcome does not depend on coatings’ conductivity.
