Fatigue mechanism in Ni3Fe single crystals with L12 superlattice structure

Ni₃Fe single crystals with the L1₂ 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 Ni₃Fe 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 Ni₃Fe single crystals. Activation of the secondary slip is closely related to the cyclic hardening/softening behaviour and the formation of PSB in Ni₃Fe single crystals.