Abstract
The hot corrosion resistance of twelve Ni-base alloys was evaluated at 873 K by three different laboratory tests; immersion test, salt coating test and embedding test. In these tests, three different corrosion ashes were employed, a sulfate (Na2SO4-K2SO4-ZnSO4), a chloride (NaCl-KCl-LiCl-CaCl2) and a chloride/sulfate mixture (NaCl-KCl-Na2SO4-K2SO4-ZnSO4). The correlations between the ranking of the corrosion resistance of the alloys in the immersion test, coating test and embedding test were investigated using spearman’s correlation coefficient. The results of the three tests were highly correlated in the sulfate and chloride/sulfate environments, whereas they were relatively poorly correlated in the chloride environment. It was found from the anodic polarization measurement and X-ray difraction analysis of the corrosion products that the relatively poor correlation is attributed to the differences in the rate-determining steps of the corrosion. In the sulfate environment, there was small difference of the corrosion mass loss among the three tests, but in both the chloride and chloride/sulfate environments, the mass losses in the coating test and embedding test were much larger than that in the immersion test. The corrosion mechnisms under the respective corrosion test conditions were discussed.
