Changes in Electrochemical Properties of Directionally Solidified Ni-base Superalloy Due to Creep and Damage Evaluation

Changes in electrochemical properties of directionally solidified Ni-base superalloy CM 247 LC due to creep have been investigated. The electrochemical polarization technique has been applied to creep-ruptured and creep-interrupted specimens under various creep condition in order to examine a detectability of creep damage. Experimental results on electrochemical polarization measurements revealed that the peak current density "Ip" and "Ipr" which appeared at a specific potential during potentiodynamic polarization reactivation measurements in dilute glyceregia solution increased with increased thermal history and showed a good correlation with Larson-Miller Parameter value. Ip and Ipr value reflected both a thermal aging effect and a stress effect, and increased with a creep life fraction. The increases in Ip and Ipr were mainly corresponded to increases in preferential dissolution rate of γ' phase at γ/γ' interface. This preferential dissolution was considered as a result from degradation of corrosion resistance of γ'phase at γ/γ'interface which may be attributable to creep damage accumulation. As a consequence, the creep damage in CM 247 LC can be quantitatively evaluated by the electrochemical technique.