Investigating material removal mechanism of an Al-Si base abradable coating in labyrinth seal system

Labyrinth seal systems are used in aero-engines to seal the clearance between turbine blades and the surrounding engine casing, and an understanding of the wear mechanism by which this occurs is necessary to achieve better sealing performance. In this work a series of tests are conducted on a high-speed test rig capable of fin tip speeds of 100 m/s. The mechanism by which the fin removes material is investigated over a range of incursion rates, with force and temperature measurements along with high-speed imaging recorded in each case. Surface examination and sectioning is also performed using microscopy post-test. The wear mechanism was found to be incursion rate dependent. At low incursion rates (0.02 µm/pass), abradable material is removed via a cyclic process, where it is first compacted in the worn groove, until ductility is lost and material fractures away from the surface of the groove. At high incursion rates (2 µm/pass), material is extruded out of the sides of the groove forming lips, before fracturing off. This process is more efficient, with lower relative forces and temperatures. As the incursion rate increases from low to high, the mechanism shows a gradual transition, with compaction being replaced with extrusion.