Orientation dependence of cyclic stress asymmetry in Ni3Ge single crystals

Abstract

Cyclic flow‐stress measurements at room temperature are performed on Ni3Ge single crystals as a function of stress and strain amplitude. The cyclic flow‐stress is found to be higher in compression than in tension for stress orientations [345] and [245]. This flow‐stress asymmetry became greater with increasing plastic‐strain amplitude when {111} slips are operative. However, in a higher strain regime (>1 × 10−4) where {001} slip systems are also activated, the stress asymmetry for orientation [345] became smaller with increasing plastic‐strain amplitude. For orientation [2 3 16], the cyclic flow‐stress is higher in tension than in compression. The cyclic‐stress asymmetry properties can be attributed to the thermally activated cross‐slip of screw dislocations from {111} to {010}. The decrease in the stress asymmetry observed in orientation [345] at the higher strain regime (>1 × 10−4) is probably caused by the change in the dominant slip systems from the octahedral to cube slips.