Cyclic stress–strain response of the ODS nickel-base, superalloy PM 1000 under variable amplitude loading at high temperatures

The cyclic stress–strain behaviour of the recently developed oxide dispersion-strengthened nickel-base alloy PM 1000 was studied under constant and variable amplitude loading conditions. Single-step tests with a constant total strain amplitude as well as incremental step tests covering the same amplitude range have been carried out at 1123 and 1273 K. The interaction of the dislocations with the fine, homogeneously distributed oxide dispersoids was found to suppress the formation of dislocation cell structures. Rather, networks with dislocations frequently pinned at the particle/matrix interface have been observed by transmission electron microscopy. However, wavy dislocation slip still contributes to the stress–strain response. Despite the similarity of the resulting microstructures, the cyclic stress–strain curve obtained from constant amplitude tests deviates slightly from the one observed in incremental step tests. While non-Masing behaviour was found for constant amplitude testing, the strong influence of the dispersoids on dislocation mobility in combination with the constancy of dislocation arrangement yields Masing behaviour for the incremental step tests.