Detection of creep damage in a nickel-based superalloy turbine bucket using eddy current imaging

Abstract

Due to elevated temperatures, excessive stresses and severed corrosion conditions, turbine engine components are subject to creep processes that limit the components life such as a turbine bucket. The failure mechanism of a turbine bucket is related primarily to creep and corrosion and secondarily to thermal fatigue. As a result, it is desirable to assess the current condition of such a turbine component. This study uses the eddy current (EC) nondestructive evaluation technique in an effort to monitor the creep damage in a nickel base superalloy, 7FA stage 2 turbine bucket after service. The experimental results show a significative electrical conductivity variations in EC images on the creep damage zone of nickel-based superalloy samples cut from a turbine bucket. Thermoelectric power measurements were also conducted in order to obtain a direct correlation between the presence of material changes due to creep damage and the electrical conductivity measurements. This research work shows an alternative nondestructive method in order to detect creep damage in a nickel-based superalloy turbine bucket.

Keywords:

• creep damage
• NDE methods
• health monitoring
• turbine bucket
• nickel-based alloy

Acknowledgement

The author would like to acknowledge P.B Nagy, University of Cincinnati, for his valuable contribution to this paper.