The influence of material properties on the wear of abradable materials

Abstract

In aero-engines it is possible for the blades of the compressor, turbine or fan to incur into their casings. At these interfaces a lining of composite abradable material is used to limit damage to components and thereby sustain the efficiency and longevity of the engine as a whole. These composite materials must have good abradability and erosion resistance. Previously, the wear mechanisms at the contact between the blade and the coating have been characterised using stroboscopic imaging and force measurement on a scaled test-rig platform. This work is focused on the characterisation of the wear mechanism for two different hardnesses of abradable lining. The established stroboscopic imaging technique and contact force measurements are combined with sectioning of the abradable material in order to analyse the material’s response during the tests. A measure of the thermal properties and the resulting temperature of the linings during the test have also been made to further understand the effect of coating hardness. The wear mechanism, material response, contact force and thermal properties of the coating have been used to characterise the different material behaviour with different hardness. At low incursion rates, with a soft coating, the blade tip becomes worn after an initial adhesive transfer from the coating. Post-test sectioning showed blade material and significant compaction present in the coating. The harder coating produced adhesion on the blade tip with solidification observed in the coating. Thermal diffusivity measurements and modelling indicated that thermally driven wear observed was as a consequence of the increased number of boundaries between the metal and hBN phases present interrupting heat flow, leading to a concentration of surface heat. At higher incursion rates, the wear mechanism is more similar between the coatings and a cutting mechanism dominates producing negligible adhesion and blade wear.