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 dispersi on-strengthened nickel-base alloy PM 1000 was studied under constant and va riable amplitude loading conditions. Single-step tests with a constant tota l strain amplitude as well as incremental step tests covering the same ampl itude range have been carried out at 1123 and 1273 K. The interaction of th e dislocations with the fine. homogeneously distributed oxide dispersoids w as found to suppress the formation of dislocation cell structures. Rather, networks with dislocations frequently pinned at the particle/matrix interfa ce have been observed by transmission electron microscopy. However, wavy di slocation slip still contributes to the stress-strain response. Despite the similarity of the resulting microstructures, the cyclic stress-strain curv e obtained from constant amplitude tests deviates slightly from the one obs erved in incremental step tests. While non-Masing behaviour was found for c onstant amplitude testing, the strong influence of the dispersoids on dislo cation mobility in combination with the constancy of dislocation arrangemen t yields Masing behaviour for the incremental step tests. (C) 2000 Elsevier Science S.A. All rights reserved.