Fatigue mechanism in Ni 3Fe single crystals with L1 2 superlattice structure

Abstract

Ni 3Fe single crystals with the L1 2 structure were cyclically deformed with various loading axes at different plastic strain amplitudes. The crystals demonstrated initial strong cyclic hardening followed by rapid cyclic softening at any orientation tested. There existed a typical plateau region in the cyclic stress–strain curves of the crystals oriented for single slip, while the saturation shear stress ( τ s) monotonically increased with increasing plastic shear strain amplitude ( γ pl) for double-slip oriented crystals. Persistent slip bands (PSBs) with cell-like dislocation structure developed in fatigued Ni 3Fe single crystals. The relationship between the volume fraction of PSBs and γ pl suggests that Winter’s two-phase model can be applied to explain the cyclic stress–strain response in Ni 3Fe single crystals. Activation of the secondary slip is closely related to the cyclic hardening/softening behaviour and the formation of PSB in Ni 3Fe single crystals.