Discontinuous creep in short-range order alloys

Abstract

A discontinuous creep process has been observed in creep studies on several complex commercial nickel-base alloys that contain chromium and an experimental binary Ni-20wt.%Cr alloy. Instead of a continuous strain-time creep curve as is normally observed, creep tests on these alloys exhibited an “instantaneous elongation” or “strain burst”, where the creep curves contained strain jumps. The studies showed that the process did not depend on gross metallurgical changes in the microstructure or on a precipitation process. It was postulated that the strain bursts are related to the formation of dislocation pile-ups in the matrix. When a localized pile-up breaks through a barrier, a dislocation avalanche results that triggers neighboring pile-ups. This process continues in neighboring grains and gives rise to the propagation of a deformation band along the gauge length in a Lüders-type deformation. It was demonstrated how the pile-up barriers could involve short-range order.