Abstract: Studies on the high temperature creep and fracture behaviours in air or in SO_2 contaminated environment for the Fe-base superalloy GH302 with flat or zigzag grain boundaries(GB) and the Ni-base superalloy Rene 80 were carried out.Although the creep rupture properties of the GH302 with zigzag GB was remarkably superior to that of flat GB in air,the properties of both droped dramatically in 10% SO_2-air environment,the creep rupture properties of the directional solidified Rene 80 were much better than that of the conventionally cast alloy in air,and also kept the same property in SO_2 contaminated environment as in air.Owing to the interaction between creep and sulphidation,the failure mechanism relates to the formation of molten Ni-Ni-3S_2 eutectic along GB,led to the premature failure of the alloy.

Key words: superalloy, grain boundary, sulphidation, oxidation, creep rupture