Response of fine-cast gas turbine blade materials to mechanical long-term stress and hot gas corrosion

Using important uncoated and coated blade materials for industrial and aircraft gas turbines the fatigue behavior and the LCF tensile swelling behaviour were examined under flowing hot gas. Gas turbine specific corrosion cases were investigated in the range of relatively high temperatures. The time-dependent strength values of the base materials are usually specified in air, so the question was whether hot gas corrosion lowers these values more strongly than can be explained by the reduction of cross section as a result of hot gas corrosion. It was also investigated whether the (Al, PtAl, CoCrAlY, CoNiCrAlY) protective layers of this combined thermal and mechanical corrosive stress can resist without premature failure. Flight turbine materials showed strong corrosion damage at 1000 degrees Centigrade under corrosion condition intensified by sea salt. Large-scale cross-section losses were found in the M 002 mod uncoated monocrystal alloy already before 1000 hours of exposure, although the fatigue strength was reduced not more than the explainable measure. Layers on the basis of Al, PtAl and CoNiCrAlY were consumed to a large extent after approximately 2000 hours. (orig./RHM)