HIGH TEMPERATURE CYCLIC DEFORMATION OF NICKEL

Abstract— High temperature cyclic deformation in nickel is investigated by comparing its cyclic hardening curves at constant strain amplitudes at four temperatures with the monotonic hardening curves and by detailed electron microscopic examination of the bulk. Just as at ambient temperature, there are broad similarities between the cyclic and monotonic hardening of nickel at high temperatures, but there are also significant differences in detail. It is shown that, as in monotonic deformation, increased dynamic recovery with increasing temperature is the main cause for the reduction in flow stress at high temperatures. However, the increased vacancy concentration produced by cyclic straining causes a linear reduction in flow stress (as distinct from the "athermal" behavior observed in monotonic deformation over a limited temperature range). Also the tendency for dislocations to agglomerate into sign-balanced, low energy configurations requires a temperature higher than that observed for monotonic deformation before high temperature softening is observed.