The GTCP331-200/250 auxiliary power unit (APU) is used to provide electrical power and compressed air for commercial aircraft, including the Boeing 757 and 767, and Airbus A310. The turbine section of this engine is a three stage axial flow configuration. Due to the combined effect of oxidation and erosion, the useful life of the first stage turbine blade may be limited by loss of material on the airfoil. The effect of material loss is reduction of the airfoil thickness and chord length.
This paper discusses a repair that restores the airfoil dimensions by buildup with a physical vapor deposition coating. The repair process includes incoming dimensional inspection of the airfoil, physical vapor deposition with tapered thickness to restore airfoil dimensions, and post deposition processing. The evaluation includes airfoil dimensional inspection, metallographic verification of coating integrity, and finite element modeling to illustrate the effect of material buildup on different locations of the airfoil.