Influence of Co to Ni ratio in γ'-strengthened model alloys on oxidation resistance and the efficacy of the halogen effect at 900 ℃

摘要

The role of base element (Co or Ni) in gamma'-strengthened single-crystalline superalloys was elucidated in the present study. Reaction kinetics during oxidation at 900 degrees C were assessed by thermogravimetry and measurements of individual layer thicknesses in the multilayered oxide scales. The development of diffusion-limiting barrier layers as well as the extent of sub-scale phase transitions could be directly correlated to the Co/Ni ratio in the alloy. For the first time a surface pretreatment with F was applied to Co-base superalloys. Apparent differences in the efficacy of the halogen effect depending on the Co content in the model alloys were observed.