Friction stress and back stress in cyclically deformed Ni3Ge single crystals

Abstract

Stress-strain hysteresis loops obtained from cyclic deformation of Ni₃Ge single crystals under strain control were analyzed. The major component of the cyclic flow stress was found to be the friction stress. The back stress was responsible for, at most, several per cent of the cyclic flow stress. The back stress was almost constant regardless of the amount of cumulative plastic strain. The origin of the back stress is attributed to a small long-range stress field of nearly uniformly distributed screw dislocations produced in the cyclically deformed Ni₃Ge single crystals. The friction stress is considered to be developed by the interaction between straight screw dislocations on parallel (111) slip planes and by the pinning of dislocations due to the thermally activated cross-slip from (111) to (010).