Investigation of Coating Performance and Corrosion of Compressor Components in the TF30-P-3 Engine of F111C Aircraft

摘要

This report examines factors involved in the degradation of the protective coating, Chromalloy S-A12, employed on the low pressure compressor stators in the Pratt and Whitney TF30-P-3 engine of an RAAF F111 aircraft. The study is confined to the 7th stage of the engine (4th stage; low pressure compressor). The stator examined had experienced considerable corrosion after only 427 hours operation. Stators on other engines are failing for similar reasons. Small corrosion nodules were present on specific areas of each stator vane coating. Sections on the outer ring or shroud were found to be corroded along a geometric arc around the 6 o'clock position of the stage. These included - (a) both surfaces of the outer shroud or ring (b) the air seal around the shroud and (c) the area underneath the air path seal or 'rub strip'. The corrosion nodules on the vanes were associated with discontinuities in the coating. These discontinuities resulted in breakdown of the diffusion coating in surrounding areas forming aluminium, chromium and iron oxides. The elements sulphur and chlorine and to a lesser extent calcium and potassium were also found in the corrosion deposits. These elements are present in the local water supply and a detergent used for aircraft washing. Examination of the compressor washing and drying procedures are recommended. Keywords: Jet engines, Aluminium diffusion coatings.