Ni3Fe Single Crystals Research Articles

Structure and Mechanical Properties of Ni3Fe Single Crystals after Severe Plastic Deformation

Structure and Mechanical Properties of Ni3Fe Single Crystals after Severe Plastic Deformation

X-ray Diffraction Data for the Study of the Multilevel Nanostructures in Ni3Fe Deformed Single Crystals

X-ray analysis has been applied for the study of the formation of nanostructures as the result of plastic deformation in Ni3Fe single crystals with the L12 structure. It was shown that the main structural changes in ordered alloys had the features similar to pure metals and the disordered solid solutions but were more complex. Structure consists of nano-crystallites divided by the antiphase boundaries forming the elements having the size a ten times smaller than the dimensions of the crystallites. After the strain of 0.18 together with the antiphase domains with the average size equal to 14 nm a small fraction of domains with an average size of 10-11 nm was revealed. After the strain of 0.38 or more, the average size of the antiphase domains was reduced to 5-2 nm.

Influence of Crystal Orientation on Ni<sub>3</sub>Fe Dislocation Structure Evolution

The dislocation structure and mechanical properties of Ni3Fe single crystals with the short range order were investigated. The laws of the dislocation structure evolution of single crystals at different deformation axis orientations were analysed. Correlation of the dislocation structure evolution with the deformation stages for the single crystals with the deformation axis orientations [001], [11], [011] and [1.8.12] was established. The role of the slipping plane numbers in the substructure evolution was revealed.

Kink Band Formation and Its Effect on Recrystallization in Ordered and Disordered Ni<SUB>3</SUB>Fe Single Crystals

In order to study the influence of ordering on deformation and recrystallization, Ni3Fe single crystals, ordered and disordered by appropriate heat treatments, were deformed in tension at room temperature and subsequently annealed at temperatures above the order-disorder transformation temperature. Both ordered and disordered single crystals exhibited a large elongation, while deformation microstructures were totally different. Kink bands formed only in the disordered single crystals. Recrystallization occurred along the kink bands. Many recrystallized grains had h111i-rotation relationships with the kink band and were twin related to each other. In contrast, no recrystallized grain formed in the single crystal deformed in the ordered state. [doi:10.2320/matertrans.48.759]

Nondestructive evaluation of dislocation structure in cyclically deformed Ni3Fe single crystals using magnetic techniques

The deformation substructure in Ni3Fe single crystals cyclically deformed at constant plastic shear strain amplitudes (γpl) consisted of two phases: the matrix with planar dislocation arrangement and the persistent slip band (PSB) having a three dimensional cell structure. The saturation stress remained almost constant regardless of γpl by adjusting the volume fraction of PSB. Anisotropy of high-field susceptibility in cyclically deformed Ni3Fe single crystals was measured in the (111) discs. Two types of magnetic anisotropy caused by atom rearrangement near the antiphase boundary (APB) and internal stress around dislocations were observed in fatigued Ni3Fe single crystals. The anisotropy data were subjected to the Fourier-type transformation and were split into separate anisotropy functions depending on the type of lattice defects. The magnitude ratio of dislocation- to APB-dependent anisotropy increases linearly with increasing γpl. This strongly suggests that Winter’s two-phase model can be applied to both mechanical and magnetic properties. Thus, nondestructive evaluation of dislocation structure in cyclically deformed Ni3Fe single crystals could be done by analyzing the magnetic anisotropy induced by cyclic deformation.

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

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.

Magnetic observation of deformation substructure in cyclically deformed Ni3Fe single crystals

The magnetic anisotropy of permeability and high-field susceptibility in Ni3Fe single crystals due to dislocations and antiphase boundary (APB) was theoretically calculated and measured by a vibrating sample magnetometer to determine the cyclic hardening and deformation substructure during cyclic deformation. Two types of anisotropy in magnetic properties were observed due to the atomic rearrangement near APB and the internal stress field around dislocations. In an early stage of fatigue where strong cyclic hardening occurred, the magnetic anisotropy was mainly due to the APB, while in a further stage of fatigue where cyclic softening occurred, the anisotropy was caused by dislocations. The cyclic softening was induced by the disordering in the localized region of coarse slip bands.

Orientation of boundaries of planar shear bands in Ni3Fe single crystals

With plastic deformation by compression up to e=0.5 in the [001] direction of fcc single crystals of Ni3Fe alloy with short-range order, we have experimentally established the spectrum of the most probable orientations of the boundaries of shear bands on the {001} faces of the specimen. We have observed that in a specimen deformed to approximately half the original length, a single system of shear bands becomes dominant within the volume of the specimen. Using the cryston approach, we give an interpretation of the observed characteristics of the evolution of the orientations of the boundaries of planar shear bands.

Role of fractal dimension in internal stress fields of Ni3Fe single crystals

In this paper, using the similarity method we have determined the fractal dimension of the dislocation structure of Ni3Fe single crystals in chaos and in the stage of cell wall formation. We have established that in chaos D=1.04, and at the walls D=1.08. For a linear dependence τ=τf+α·G·b·ρ1/2, the internal stresses increase by a factor of 1.1 in chaos and 1.22 in the cells, while the internal energy increases by a factor of 1.22 and 1.48 respectively. We discuss the mechanisms for roughening the dislocation structure.

The effects of test temperature on the work-hardening characteristics of Ni3Fe ordering single crystals oriented for multiple slip

Results are reported on the temperature dependence of work-hardening characteristic of Ni3Fe single crystals in the ordered and disordered states; there is a slight anomaly in the temperature dependence of the yield stress in stage II in both states, and the same applies to the relative hardening factor ΘΠ/G.

Tensile Behavior upon Ordering of Ni3Fe Single Crystals

AbstractThe tensile properties of ordered and disordered Ni3Fe single crystals have been investigated. Also, polycrystalline specimens have been tested to show the influence of grain size on the deformation characteristics of Ni3Fe. Measurements have been made to determine the influence of parameters such as the initial orientation of the tensile axis of single crystals, the ordered domain size, and the test temperature on the mechanical properties of Ni3Fe. Tensile axis reorientation during deformation was followed with X‐ray techniques. It was found that in ordered single crystals, the measured tensile axis rotation agrees well with the calculated values if one activated glide system is assumed. The influence of secondary slip on the tensile characteristics of ordered crystals was determined by using specimens oriented for multiple glide. It is demonstrated that the work hardening rate increases with the occurrence of secondary slip. The strain‐aging phenomena shown previously in polycrystalline Ni3Fe was found to occur also in single crystals. The nature of the observed effects in ordered Ni3Fe is interpreted in terms of the antiphase boundary tube mechanism.