Failure analysis of gas turbine buckets

The failure of a gas turbine first stage bucket was investigated by visual inspection and finite element analysis. The failure of a major bucket cooling passage was a critical cause of the separation of a bucket segment and caused microstructural deterioration of the neighboring regions by serious thermal load. Changes of microstructural morphologies of the damaged buckets under the thermal and mechanical stress were observed. After coating stripping, the bucket surface condition was evaluated through visual inspection and finite element analysis. The TMF (thermal-mechanical fatigue) cracking of surface coatings on the suction and pressure sides of the bucket was described.