Abradable coatings for enhancement of Aeroengine efficiency

Abradable coatings reduce blade tip clearance in an axial flow compressor (used in all aero engines) and thereby increase operating efficiency. The clearance between blade tips and the casing must account for thermal and internal expansion as well as changes in concentricity due to shock loading events, to prevent catastrophic tip to casing contact. Therefore the role of Abradable coating is not only to allow for closer clearances, but to automatically adjust clearances, in-situ, to accept physical events and/or thermal variation that may be found during it's exploitation According to an estimation published in SAE, USA Abradable coating improves the air compressing efficiency by 15-25% thereby improving life of the engine by 5-10%. An Abradable coating must have sufficient strength and hardness to resist the ruggedness of aero engine handling during assembly, transportation and exploitation. At the same time it must be soft enough to allow the axial flow compressor rotor blades to cut through it easily, without getting pilled off in lumps. To achieve this typical application requirement which are very stringent is a difficult task.