Application of Al/Si abradable coatings with a metallic foam substrate for aero-engine sealing

This work aims to investigate the wear mechanics of a conventional abradable material (Metco 320) used for compressor sealing between the blade and surrounding casing, backed by an open-cell metallic foam substrate, determining whether the use of the foam backing material results in a rub compliant liner. Testing is carried out on a scaled-down high-speed rig to create engine-like conditions to understand how the capped metallic foam deforms and compacts. The metallic foam substrates are NiCr-based alloys, and this study compares the effects of abradable cap hardness, incursion rate and foam pore size on the behaviour observed. In situ measurement techniques have been utilised to observe the wear mechanic present, with these including force measurement as well as high-speed imaging. Softer capped foams were seen to show higher levels of compaction and compression, forming a concentric track in response to the rub event, when in comparison to a harder cap. Similarly, faster incursion rates performed best in terms of material actuation, with this linked to the large energy input per strike of the blade. Pore size showed a significant impact ability of the hybrid system to accommodate the rub, where coarse flexible foams performed better than fine stiff ones.