1993 Volume 42 Issue 2 Pages 86-92
Hot-corrosion susceptibility was investigated for the alloys whose compositions laid on a tie-line of a γ/γ′-two-phase Ni-Cr-Al-based alloy by a burner-rig-test (BR-test) in a combustion gas containing Na2SO4 and dip-tests in a Na2SO4/NaCl-salt mixture. Severity of corrosion differed for both tests in regions of γ′-phase content of I: <50%, II: 50-100% and III: >100% (γ′-phase). Relative severity among the regions was not identical between the BR-test and the dip tests. In the case of the BR-test, the corrosion was moderate in the regions I and III and the most severe in the region II, especially at a γ′-phase content of 85%. This is presumably because chromia and alumina are effective in retarding the corrosion respectively in the regions I and III, while both are less so in the region II. In the case of dip tests, the corrosion was very mild in the region I, considerable in the region II and cataststrophic in the region III. This is considered to be caused by loss of protective effect of alumina in the region III due to the basic fluxing owing to low oxygen content in the salt. The above information suggests that unfairly pessimistic results than would be materialized in gas turbines might follow, if hot corrosion susceptibility of nickel-base alloys or nickel-aluminide-based materials is assessed by dip tests.
