Cyclic Deformation and Fracture Behavior of L1_2-Type Intermetallic Compounds Using Magnetic Properties

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Cyclic deformation behavior and fracture mechanism in Ni_3Fe and Ni_3(Al,Ti) single crystals with the L1_2 structure were examined focusing on the cyclic hardening/softening curves, the deformation substructure and changes in magnetic properties due to dislocations and planar faults.In a disordered state, Ni_3Fe showed monotonically cyclic hardening during cyclic loading. In contrast, ordered Ni_3Fe single crystals exhibited cyclic softening after initial cyclic hardening. In the stage of cyclic hardening, the well-developed persistent slip bands were observed by transmission electron microscopy. Magnetic properties were influenced by the interaction between magnetic spins and internal stress around dislocations. Using the magnetic anisotropy in fatigued Ni_3Fe single crystals, dislocations and planar faults were determined. At the initial stage of cyclic hardening, the to-and-fro motion of dislocations as a pair combined by an anti-phase boundary occurred. Deformation was concentrated in the PSB region and the disordering occurred in the localized PSB region. The localized disordering induced the cyclic softening. The localized deformation initiated a micro crack resulting in fracture of crystals.