Low-cycle-fatigue behaviour of superalloy blade materials at elevated temperature

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Abstract
The low-cycle-fatigue (LCF) behaviour of superalloys has been examined with particular emphasis on their early stage strength changes and their response to complex cycling. Using steels and a titanium alloy as comparators, it has been possible to establish some general guidelines regarding their LCF performance. In the normal testing domain (700–1000°C) a high yield strain results in predominantly elastic conditions and cyclic stability. Under strain controlled dwell testing superalloys are fatigue dominated and generally more sensitive to compressive hold periods, whereas under stress control shortest lifetimes result from tensile dwells. Environmental influences are strong especially at temperatures where oxides remain brittle, but at high temperatures (>900°C) overaging effects may be beneficial. During thermal–mechanical cycling in-phase testing appears most deleterious. MST/516