Yu. A. Abzaev

Evolution of the dislocation structure and the hardening mechanisms of multiple slip oriented Ni3Ge single crystals

We studied the evolution of the dislocation structure of Ni3Ge single crystals deformed by compression at room temperature. It is shown that the distribution of dislocations is spatially uniform in the studied alloy. The uniformity in the dislocation distribution is produced by relatively high amounts of the frictional stresses of the dislocations. On the basis of the obtained values of the dislocation structure parameters, the contributions of the various mechanisms in the dislocation drag are determined. It is shown that the resistance to deformation is determined primarily by overcoming reactive and unreactive “forest” dislocations, the total contribution of which is 0.9 of the applied stress.

Accumulation of dislocations and thermal strengthening of alloys having an L12 superstructure

This paper discusses the dislocation-accumulation mechanism in alloys having an L12 superstructure, which is associated with the formation of Kira-Wilsdorf barriers and the retardation of superdislocations during plastic deformation. A model of the dislocation-accumulation kinetics during plastic deformation is constructed, on the basis of which a mathematical model is formulated for the thermal and deformation strengthening of single crystals of alloys having the L12 superstructure. The results of numerical calculations based on the model are compared with the experimentally observed regularities of the deformation and thermal strengthening of single crystals of Ni3Ge.

Effect of orientation on the peak temperature of the yield-stress anomaly in single crystals of the Ni3Ge alloy

Temperature dependence of the yield stress τc(T) and shear stresses, as well as the orientation dependence of the peak temperature Tp of the yield-stress anomaly have been studied on single crystals of the Ni3Ge alloy. The peak temperature Tp corresponds to the maximum in the τc(T) dependence. Profiles of the Tp isolines have been determined based on the equality of the values of the yield stress in the octahedral and cube planes of cross slip. It is shown that in the case of the above equality it is possible to describe the orientation dependence of the peak temperature Tp of the temperature anomaly of the yield stress in single crystals of Ni3Ge.

Evolution of dislocation structures having various orientations in strained single crystals of the alloy Ni3Ge

The dislocation structure of strained single crystals of Ni3Ge with various orientations is investigated by electron microscopy. The evolution of the dislocation structure parameters is studied as a function of the degree of strain, temperature, and orientation of the single crystals. Analysis of the experimental dependences of the yield stress on the density of dislocations leads to certain conclusions about how various mechanisms for dislocation drag make temperature-dependent contributions to the deforming stress, and about the nature of the thermal hardening of Ni3Ge.

Analysis of fragmentation of deformation in Ni3Ge single crystals

The strain distribution on two faces ofNi3Ge single crystals compressed to a strain ε-14.16% at T=77.673K was studied by the grid method. It is shown that temperature has a significant effect on the strain distribution. Fragmentation of local strain due to shape change in specimens during active loading was established by the method of main components.

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.

Simulation of the structural state of amorphous phases in nanoscale SiO 2 synthesized via different methods

The structural state in nanoscaled SiO2 is probed experimentally via X-ray diffraction and the simulation method. The aerosil nanoparticles and nanoparticles synthesized via the electron beam evaporation are compared. The nanoparticles for all samples are shown to be in the amorphous state. The amorphous state of a SiO2 unit lattice is simulated via the molecular dynamics. The full-profile refinement of parameters for a simulated SiO2 phase (the Rietveld method) has allowed the complete structural information to be established at varying the specific surface. The unit cell parameters, the spatial atomic distribution and the degree of cell node occupation are determined, as well. The specific surface area is shown to decrease in aerosil nanoparticles and to increase in tarkosil nanoparticles with the increasing binding energy of atoms in a cell.

Stress Distribution in a Slip Trace of Deformed Ni3Ge Single Crystals

The shear‐stress distribution produced by distortion of Ni3Ge single crystals under compression is studied. The evolution of the dislocation structure during deformation of Ni3Ge single crystals of various orientations ([2¯34], [1¯11]

Analysis of Similarity of Dislocation Interactions in Single Crystal Ni3Ge

, [1¯39], and [001]) at T = 77, 293, 523, 673, and 873 K is analyzed. It was found that, up to failure strains, the dislocation structure is characterized by a uniform dislocation distribution. Regardless of the strain‐axis orientation, the linear relation τ = f(ρ0.5) is valid for all the test temperatures except for T = 77 K. The deviation from the linear relation at T = 77 K is due to the suppressed thermally activated slip of dislocations in nonuniform‐strain fragments at the specimen edges. In these fragments, the shear stresses are substantially reduced, and hence, the stresses produced by the dislocation cluster retard the development of slip in this trace.

Local strain distribution in Ni3Ge crystals

Using the methods of diffraction electron microscopy and mechanical testing, the evolution of dislocation structure accompanied by deformation of single-crystal Ni3Ge with different orientation of the axis of straining is studied at a range of temperatures. A linear relationship between shear stress τ and dislocation density ρ0.5 is established. An analysis of the similarity of dislocation interactions is conducted in Ni3Ge over a range of temperatures with developed octahedral and cubic slips, i.e. up to the anomaly peak temperature and higher, respectively. It is found out that under the octahedral slip, the dislocation interactions up to fracture deformations are similar at different temperatures in question. The similarity is also observed within the temperature range with developed cubic slip.