Segregation of alloying elements of directionally solidified nickel based superalloy CM247LC during creep degradation process

The mechanism of the degradation process of nickel based superalloy CM247LC under creep loading was analyzed by considering the microscopic chemical composition of the material such as phase boundary of γ and γ′ phases. In this study, a Directionally Solidified (DS) nickel-based superalloys CM247LC was used as test specimens. The creep test was performed at 900°C under an uni-axial stress of 216 MPa. Each specimen was creep ruptured and interrupted at different hours and then analyzed. The change of chemical composition around the interface analyzed precisely by used Auger Electron Spectroscopy (AES). It was found that the local enrichment or lack of cobalt and chromium was found at the interface. This tendency was not found in the stress free area. Since chromium is the well-known element that dominates the degradation of this material, such an enrichment or lack of cobalt and chromium may play an important role for forming a crack propagation path near the interface. This local segregation should be analyzed further to make clear degradation mechanism of this material.