Early stages of scale formation during oxidation of γ/γ' strengthened single crystal ternary Co-base superalloy at 900 ℃

摘要

A study on the individual role of gamma and gamma'-phase during the scale formation on Co-9Al-9W (at.%) at 900 degrees C was conducted. High-accuracy thermogravimetric analysis was used to locate changes in the kinetics of scale growth. Compositions of three separated layers within the scale have been elucidated in detail. The results demonstrate the substantial impact of the two-phase microstructure on the initiation of oxidation for the appearance of the scale. Examination of STEM-EDX elemental mappings of the internal oxidation front during the early stages of scale growth can explain the origin of isolated Al2O3 precipitates instead of a closed protective layer.