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

研究了L12结构的Ni_3Fe和Ni_3（Al，Ti）单晶的循环形变行为和断裂机制，着重研究了循环硬化/软化曲线、形变亚结构以及位错和面错引起的磁性能变化。而有序Ni_3Fe单晶在初始循环硬化后出现循环软化。在循环硬化阶段，透射电镜观察到了非常发达的持久滑移带。磁性能受磁自旋和位错周围内应力的相互作用影响。利用疲劳Ni_3Fe单晶的磁各向异性，确定了位错和平面缺陷。在循环硬化的初始阶段，位错以反相边界的形式成对往复运动。形变集中在PSB区，无序发生在局域PSB区。局部无序化导致循环软化。局部变形引发微裂纹，导致晶体断裂。

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.