By Lijue Xue, Matt Donovan, Yangsheng Li, Jianyin Chen, Shaodong Wang and Glen Campbell

Jet engines need to run as hot as possible to extract maximum energy from fuel. Combustion components are subjected to extremely harsh environment, running at elevated temperature with high vibration and pressure, which results in varying degrees of wear and fretting. Interface surfaces on combustion parts, such as the air caps of fuel nozzles, frequently are worn beyond use and must be replaced during overhaul. Repair and replacement of these components can be very expensive and time consuming.

National Research Council Canada (NRC) has developed precision laser additive manufacturing technology for repair of worn gas turbine components. The repair system uses integrated 3D mapping and laser additive deposition. Through a joint effort by NRC and UTC Aerospace Systems, a case study was performed to evaluate the feasibility of repair of worn fuel injectors from a land based gas turbine engine. The project evaluated the use of laser cladding of cobalt alloy L-605 for repair of worn fuel injectors on a Rolls Royce 501K engine. Testing results reveal that laser-clad L-605 layer is dense and metallurgically bonded to the wrought L-605 substrate. The fatigue life of laser clad L-605 on wrought L-605 substrate is comparable or even substantially improved as compared to the baseline wrought L-605 specimens at elevated temperature (538oC). The improved fatigue life of the laser-clad L-605 specimen may be attributed to its very fine microstructure and increased hardness. The laser-clad L-605 material also shows comparable sliding wear resistance as the wrought L-605 baseline material.

The integrated inspection and laser additive repair system was used to repair the damaged 501K fuel nozzles, which is capable of inspecting and repairing a worn gas turbine injector less than one hour. The repaired RR501 fuel nozzles passed dye penetration and X-ray inspection. Further work will be conducted to qualify the laser cladding repair process for the RR501K fuel nozzles. This innovative system dramatically reduces repair time and cost of high value gas turbine components.

Figure a

RR501K fuel nozzle air cap (a) as-damaged.

Figure b

RR501K fuel nozzle air cap (b) after cladding repair and final machining.

Lijue Xue, Yangsheng Li, Jianyin Chen, Shaodong Wang and Glen Campbell are with the National Research Council Canada. Matt Donovan is with United Technologies Aerospace Systems.