Distribution of slip tracks in single crystals of Ni3Fe alloy

The results of an experimental investigation of the distribution of slip tracks in a primary system in single crystals of Ni₃Fe alloy, oriented for a single slip, are presented. Investigations were carried out over a range of scales which differed by three orders of magnitude. Histograms of the distances between slip tracks at different scale levels are constructed. Self-similar track distributions in the primary slip system over the range of scales investigated are established. Tomsk State Architectural-Construction University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 51–56, April, 1998.     

Orientation of boundaries of planar shear bands in Ni3Fe single crystals

With plastic deformation by compression up to ε=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. Urals State Wood Technology Academy. Tomsk State Architectural Design Academy. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 62–67, August, 1997.     

Constricted hysteresis loops in Fe and Ni single crystals

Magnetic hysteresis loops reflect the variety of magnetic domain structures and have been considered to have normal rectangular or leaf-like shapes in standard ferromagnets such as Fe and Ni metals. We report on observations of constricted hysteresis loops in Fe and Ni single crystals with very low defect densities. The constricted loops were observed below T=150 K and in a medium temperature range from 150 to 430 K in Fe and Ni single crystals, respectively. These constricted loops disappear by weak plastic deformation for both single crystals. The origin of constricted hysteresis loops was explained by eddy current effects under less domain wall pinning due to dislocations.     

Discontinuous deformation of Ni3Fe alloy single crystals in various states of atomic order

The conditions conducive to discontinuous deformation of alloy single crystals in various states of order were studied in experiments. An equation defining the minimum temperature for deformation discontinuities to develop was obtained. The possible reasons for the influence of order upon discontinuous deformation were analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 65–71, December, 1977.     

Ni52Mn24Ga24单晶中取向内应力的热动力学计算

测量了Ni52Mn24Ga24单晶样品在磁场加载和未加载情况下马氏体相变时的相变应变.分析结果表明:用提拉法生长单晶时在晶体内部引入了单一取向的内应力,该取向内应力可诱导马氏体变体择优取向,从而导致马氏体相变时产生大的相变应变.从理论上计算了该内应力的大小.另外,对样品在马氏体态单纯磁诱导应变的热动力学研究,表明取向内应力在马氏体态依然存在.     

Change of superdislocation splitting with strain in single crystals of the Ni3Fe ordered alloy

The method of transmission electron microscopy is used to study the dislocation structure in single crystals of the Ni ₃ Fe ordered alloy for different degrees of strain. The [1812], [011], [111] and [001] single crystal orientations are examined. The superdislocation splitting (r) is measured for different degrees of strain, distributions of r are constructed, and their average values 〈r〉 are estimated. The 〈r〉-ε curves are constructed. With the use of the experimental r values, the effective energy of antiphase boundaries ζ* is estimated. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 51–56, January, 2006.     

Thermally activated mechanisms of plastic deformation of single crystals of the disordered alloy Ni3Fe

On the basis of experiments on the variation of temperatures in the process of deformation and relaxation of stresses, we make an analysis of the temperature dependence of the yield stresses of single crystals of the disordered alloy Ni₃Fe and of the nature of the processes determining it.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 109–113, July, 1978.     

A crystal plasticity finite element model for flow stress anomalies in Ni3Al single crystals

This paper presents a dislocation density-based non-Schmid constitutive model to address the anomalous thermo-mechanical behaviour of the L1₂ intermetallic single-crystal Ni₃Al. Ni₃Al is used as a strengthening precipitate (γ′ phase) in Ni-based superalloys. Addressing such anomalous behaviour by accounting for temperature-dependent flow stress and hardening evolution, as well as orientation-dependent tension–compression asymmetry, is necessary for modelling superalloys across a range of temperatures. While hardening in cube-slip systems results from statistically stored dislocations (SSDs), hardening in octahedral slip systems is due to both SSDs and cross-slip dislocations (CSDs). The constitutive model incorporates hardening evolution due to SSDs and CSDs. Experimental data for Ni₃Al-type single crystals, available in the literature, are used to calibrate material parameters. Subsequently, results of crystal plasticity FEM simulations are compared with experimental data for several orientations under constant strain rate and creep loading conditions for a wide range of temperatures. The model is able to correctly predict the response of L1₂ intermetallic single crystals including features of anomalous flow stress and non-Schmid yield behaviour.     

Influence of normal stress on yielding behaviour in Fe -3 ·2% Si alloy single crystals

Specimens of Fe-3·2 wt% Si alloy single crystals of various orientations, both with 18 ppm C and decarburized, have been deformed in compression ( \(\dot \varepsilon \) ～ 10^?4 s^?1) at different temperatures between 125 K and 293 K. It has been found that the magnitude of CRSS, the choice of the slip planes and the shape of the stress-strain curves depend on the angle between the compression axis and the Burgers vector (angleξ). The stress normal to the maximum resolved shear stress plane is strongly altered on changing the angleξ. The discussion of the obtained experimental results seems to indicate that the normal stress influences the structure of screw dislocation core and subsequently the dislocation mobility.     

Role of fractal dimension in random walks on scale-free networks

Fractal dimension is central to understanding dynamical processes occurring on networks; however, the relation between fractal dimension and random walks on fractal scale-free networks has been rarely addressed, despite the fact that such networks are ubiquitous in real-life world. In this paper, we study the trapping problem on two families of networks. The first is deterministic, often called (x,y)-flowers; the other is random, which is a combination of (1,3)-flower and (2,4)-flower and thus called hybrid networks. The two network families display rich behavior as observed in various real systems, as well as some unique topological properties not shared by other networks. We derive analytically the average trapping time for random walks on both the (x,y)-flowers and the hybrid networks with an immobile trap positioned at an initial node, i.e., a hub node with the highest degree in the networks. Based on these analytical formulae, we show how the average trapping time scales with the network size. Comparing the obtained results, we further uncover that fractal dimension plays a decisive role in the behavior of average trapping time on fractal scale-free networks, i.e., the average trapping time decreases with an increasing fractal dimension.     

Orientation dependence of texture evolution in cold-rolled Ni3Al single crystals

Texture evolutions of cold-rolled thin foils of binary stoichiometric Ni₃Al single crystals were examined as a function of the initial crystal orientation. In the cases of the initial rolling direction (RD) close to ?001?, a double {110} {112} texture associated with a banded structure tends to develop irrespective of the initial foil normal direction (ND). The macroscopic shape of these foils with the banded structure is straight and simply elongated along RD, keeping their rectangular shape. In contrast, when the initial RD is close to {112}, the texture and the microstructure are rather uniform without the texture splitting and the banded structure formation. The foils of group B are macroscopically curved, twisted and eventually cracked from the side edge of the samples. Tendencies of the lattice rotations vary with the initial ND in the latter case. According to the plastic strain analysis, the formation of the banded structure is found to be essential for fabricating the thin straight foils in the case of the cold rolling of Ni₃Al single crystals.     

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 /G.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 24–28, October, 1977.     

Effect of heat transfer mode on the temperature and thermal stress fields in single crystals

Different modes of conjugate heat transfer in a crystal environment–growth chamber walls system with geometry similar to the upper part of a Czochralski thermal unit are investigated numerically. Calculations are performed for an argon Prandtl number of 0.68 and a Grashof number of 16000. The thermal stress fields in the crystal are calculated using the resulting temperature fields.     

Effect of a magnetic field on the flow stress of Co and Fe single crystals

In a range of plastic deformation, the flow stress drop and the stress relaxation of Co and Fe single crystals are observed under an a.c. magnetic field. The magnitude of these drops is discussed on the basis of different deformation modes due to the crystal structure.     

Theoretical study of the environmental effects on the hyperfine fields of Ni and Fe in Ni0.75Fe0.25

The dependence of the hyperfine fields B_hf of Ni and Fe in Ni_0.75Fe_0.25 on the surrounding atomic configuration has been studied by performing charge selfconsistent 6 shell-cluster Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA) bandstructure calculations. By replacing the CPA- scatterers in the various shells around the central atom by Ni - or Fe-atoms, respectively, it could be shown that the hyperfine fields vary linearly with the number of Fe-atoms within a given shell and that the changes of B_hf due to simultaneous changes of the atomic configurations of different shells are additive. The changes of the hyperfine fields upon ordering of Ni_0.75Fe_0.25 solid solution as deduced from our calculations agrees reasonably well with experiments.