High speed wear testing of an abradable coating

A high speed test rig has been made for analysis of the wear of abradable coatings. Impact velocities between 100 and 200 m s−1 and incursion rates between 3.4 and 2000 μm s−1 have been used. Further characterisation of the wear process has been performed using image analysis of the blade, stroboscopic imaging of the abrasion and SEM of the blade. It was found that incursion rate had a far greater influence on the wear mechanism, with tests at high incursion rates showing little wear or adhesion, whereas tests at low incursion rates showing significant adhesion and wear. The wear patterns found were consistent with those found in abradable coatings in aero-engine compressor casings. It was shown that bulk measurements of mass and length change were inadequate in characterising the nature of the wear processes encountered during the test, with more accurate characterisation found by image analysis of the blade. This analysis, together with SEM pictures of the blade tip, showed that both wear and adhesion occurred during the same test; this was characterised by the arithmetic surface roughness and change in average blade length. Stroboscopic imaging of the build-up showed that at low incursion rates the build-up of adhered material does not occur uniformly during the incursion, with the rate of build-up being greater than the incursion rate at points. This suggests that the adhesion of abradable material is due to plucking out of complete phases from the abradable coating, rather than a conventional cutting mechanism.