Defect microstructure in titanium nitride submicrocrystals

Transmission electron microscopy has been applied to the defect structure of titanium nitride in the submicrocrystalline (SMC) state produced under conditions of deviation from equilibrium in ion-plasma synthesis. The submicrocrystals contain a new type of defect substructure having a continuum disclination density up to 2.5 rad/μm². Direct structure methods give evidence for a high density of partial disclinations at the SMC grain boundaries in the nitride phase. A novel method has been used to examine substructures having a high defect density, which has been used to estimate the partial disclination density at the submicrocrystal boundaries. The origin of this highly defective state and the effects of it on the properties of SMC materials is discussed. Kuznetsov Siberian Technical Physics Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–12, July, 1998.     

Fatigue failure mechanism of polycrystalline materials at the mesoscopic level

Systematic studies of the mesoscopic mechanisms of deformation of polycrystalline materials of lead and its alloys have been carried out under conditions of sign-alternating bending at room temperature. It has been shown that fatigue failure is due to the evolution of vortices of mesoscopic substructures. Multiple slip separated in adjacent grains is the basis for this kind of deformation. This causes extremely strong localization of the displacement in individual favorably oriented grains and self-organization of these grains in agreement with regular structural levels of deformation. In polycrystalline lead, the mesoscopic substructure has a block character, with each block containing several grains. The elements of such substructures are nucleated in stress mesoconcentrator zones which arise at the grain boundaries under conditions of intense grain boundary slippage. In the course of cycling they gradually propagate through the whole transverse cross section of the sample, which completes its failure. Alloying substantially changes the character of the mesoscopic substructures which are formed. We have considered the different types of vortex mesoscopic substructures and studied their connection with cyclical endurance of the alloy. Recommendations for increasing the fatigue endurance of plastic polycrystalline materials are given. Institute of the Physics of hardening and Materials Science, Siberian Section, Russian Academy of Sciences. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 40–57, June, 1996.     

Laws of substructural and phase transformations in the plastic deformation of martensitic steel

Substructural and phase transformations in the course of plastic deformation in tempered 34KhN3MFA steel are considered. A relation is established between the type of substructure and the phase state of carbon. A direct relation is established between the carbon content in the solid solution and the crystal-lattice distortion. The carbon concentration at dislocations and fragment boundaries is determined.Tomsk State Architectural and Building Academy. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 76–82, April, 1994.     

Plasticity and strength of solids

This article reviews research conducted over the past 15 years at the intersection of the physics and mechanics of a deformable solid on the basis of the concept that plastic deformation and failure represent the evolution of shear-stability loss of a loaded material at various scale levels. This research has led to the founding of a new scientific discipline: the physical mesomechanics of materials, in which a deformable solid is regarded as a multilevel self-organizing system. The development of mechanisms and stages of plastic deformation at different scale levels conforms to the principle of scale invariance. This qualitatively changes the methods of describing the plastic deformation and failure of solids. The most pressing areas of research in the physical mesomechanics of materials are noted; these will determine the basic trends in research on the strength of solids in the next decade. Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 7–34, January, 1998.     

Realistic problems in the physics of plasticity and hardness for single crystals and polycrystalline materials

The basic results from investigations of certain real problems in the physics of plasticity for single crystals and polycrystalline metal alloys carried out under the direction of the authors are given. The microdeformation patterns and formation of the flow limit in polycrystalline material are treated; the features of the mechanisms of deformation, deformational hardening, and the defect substructure in high-strength metal alloys are characterized. Analyses are carried out for phenomena involving activation of grain boundaries by grain boundary flows of impurity atoms, and experimentally based features of deformation on different structural levels under active extension, creep, and sign-alternating loading conditions. The main attention is given to the development of collective deformation modes. A discussion of some structural aspects of the realization of meso-level plastic flow with different deformation conditions is presented. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 5–15, August, 1998.     

Methodology of physical mesomechanics as a basis for model construction in computer-aided design of materials

Conclusions The basic theses concerning the methodology of physical mesomechanics considered in this review show that a deformable solid can be represented as a microlevel system of self-consistent deformation structural elements of different scales. The law of scale invariance allows us to describe the behavior of very different materials under different loading conditions based on the element base for the scale levels of a deformable solid. The motion of volume structural elements of the deformation is described by the equations of mechanics (mesolevel and macrolevel), accommodation processes within the SEDs and on their boundaries — dislocation theory (microlevel). We have formulated an algorithm for construction of models for such multilevel systems which can be used in computer-aided design of materials. Examples of the classification of different structural materials have been presented based on the proposed algorithm.This work was done with the support of the Russian Foundation for Basic Research, Project No. 9301-16498.Institute of Physics of Strength and Materials Science, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 6–25, November, 1995.     

Grain size refinement due to relaxation of disclination junction configurations in the course of plastic deformation of polycrystals

A model is proposed for the formation of the substructure in polycrystals during plastic deformation. According to this model, fragmentation of a grain occurs through the formation of a system of diagonal low-angle boundaries, which originate at the edges of a rectangular grain. Misorientation boundaries form through relaxation of a nonsymmetric junction quadrupole disclination configuration accumulated at the grain corners under severe deformation when the disclination strength reaches a certain critical value. The energetics of this process is analyzed. A general case is considered where the disclinations at the junctions of the chosen grain differ in strength. The energetic approach used makes it possible to determine the misorientation angle ω_x of the resulting boundaries corresponding to the maximum energy gain and to find the dependence of this angle on the degree of asymmetry of the quadrupole configuration of junction disclinations. According to the proposed model, the splitting of a grain with a short edge greater than 0.5 μm is energetically favorable and decreases the latent energy of the grain for any ratio between the junction disclination strengths if the grain length-to-width ratio is less than 30. It is shown that the minimum possible grain size in the proposed model does not exceed 0.1 μm.     

Influence of nonhydrostatic stresses on the development of martensitic transformations and inelastic strains at various levels in Ti(Ni-Cu-Fe) polycrystalline intermetallic compounds

The levels of inelastic martensitic strain of polycrystals during a thermoelastic martensitic transformation under a load are discussed. The example ofTi(Ni-Cu-Fe) alloys with the B2 structure was used to study the role of microlevel and mesolevels in inelastic martensitic deformation during cooling of polycrystals under a load and loads in different initial structural states. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Institute of Physics of Strength of Materials and Materials Science, Siberian Branch of the Academy of Sciences of the USSR, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, p. 35–46, January, 1998.     

Dynamics of plastic deformation: Waves of localized plastic deformation in solids

Conclusions It has been shown here that a localized plastic deformation in structurally inhomogeneous media can be of a wave nature and can propagate in the form of nonlinear plastic waves, not only at the microscopic level but also at the mesoscopic level. It has been established that there is an interrelationship between this new effect and grain-boundary slippage (an effect which has been under study for a long time) and also with certain types of quasiviscous fracture in plastically deformable materials.We have discussed certain specific practical problems in the mechanics of plastic deformation, and for certain types of fracture. In the future, these problems will be discussed at a more profound level and in greater detail, because of experimental studies which are presently being carried out on the dynamics of deformation for various types of loading and fracture [17, 18, 31]. We hope that the approach proposed here for a theoretical study of the localization of deformation and fracture can be taken to study such effects as splitting off [31], the influence of defect fluxes on grain-boundary slippage [22], superplasticity [23], the behavior of tectonic faults and boundaries of various types [32], electroplastic and magnetoplastic effects, and high-temperature localization of deformation [25].The general nature of the approach proposed here results from the circumstance that a localization of deformation is present explicitly or implicitly during plastic deformation, and the behavior of this deformation plays a role of fundamental importance in the propagation of plastic deformation through a material.The author wishes to thank V. E. Panin for a constant discussion of this problem and I. O. Nedavnii for carrying out the numerical calculations.V. V. Kuibyshev Tomsk State University. Institute of Strength Physics and Materials Science. Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 19–41, April, 1992.     

Mesomechanics of plastic deformation and fracture of partially crystalline polyethylene

From the standpoint of physical mesomechanics, we have investigated plastic deformation mechanisms and the mechanical properties of partially crystalline polyethylene. We show that from the very beginning, plastic deformation occurs at the mesoscopic level. Fracture is preceded by fragmentation of the material. The observed stages of the process of plastic deformation of polyethylene are qualitatively similar to the stages of this process for metallic materials. The effect of electron bombardment on the mechanical properties of polyethylene is explained by the size reduction in the mesoscopic substructure formed on plastic deformation. Tomsk Polytechnical University. Zhilin University, People’s Republic of China. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 48–53, January, 1997.     

Relaxation processes in metals at high strain rates

Mathematical modeling is used for experiments involving the loading of plates by plane shock waves to study the relaxation of shear stresses during the high-rate deformation of metallic materials. It is established that the characteristic relaxation times vary broadly — from fractions of a nanosecond to several microseconds. Such variation is indicative of a change in the mechanism responsible for relaxation. As a result, there is a difference between the quasi-equilibrium shear stresses in the elastic precursor and the same stresses behind the shock front. Metallic materials remain capable of resisting plastic deformation behind the front. Structural irregularities created by high-rate deformation result in localization of plastic flow at the microscopic level, which in turn causes the parameters of the stress-strain state at this level to differ from the corresponding parameters on the macroscopic scale.Siberian Physico-Technical Institute, affiliated with Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 82–90, August, 1995.     

Nature of the temperature dependence of plasticity in the polycrystalline intermetallic compound Ni3Al

The effect of temperature on the plasticity, the type of failure, and the fractions of brittle intercrystallite and viscous transcrystallite failure of the intermetallic compound Ni-24 at. % Al have been studied with boron and without boron. A method is proposed for determining the cohesive strength of the grain boundaries by using the parameters of the flow curve and taking account of the local plastic deformation at the tip of the crack. It is shown that the cohesive strength of the grain boundaries is quite high in Ni₃Al and it is not the cause of the low-temperature embrittlement. The temperature dependence of the plasticity in the Ni-25 at. % Al alloy with boron and without boron in the region of the anomalous temperature dependence of the flow limit is determined by the change in the deformational hardening coefficient and at higher temperatures by a lowering of the cohesive strength of the grain boundaries.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk University. Institute for Strength and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 80–89, November, 1994.     

Formation and development of laser physics at Tomsk University

The formation of the laser school in the Siberian Physical-Technical Institute at Tomsk State University is considered in historical perspective. The most important achievements and publications are discussed. The role of Siberian Conferences on Spectroscopy held regularly under the supervision of Prof. N.A. Prilezhaeva in the development of laser physics at Tomsk University and in the city of Tomsk is demonstrated. Tomsk State University; the V. D. Kuznetsov Siberian Physical-Technical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 4–13, August 1999.     

The effects of substructure on fatigue crack propagation

The correlation between the initiation and propagation of fatigue cracks and the substructure formation was examined using aluminium specimens. The effects of substructures introduced by static and alternating stresses and those of the recovery of the substructure on the propagation rates of fatigue cracks were also studied. Observations of the substructures were made by means of the X-ray micro-beam technique. The principal results obtained are as follows:

1. At the time of fatigue crack initiation a definite substructure develops at the root of a notch made on the specimen edge.
2. The rate of fatigue crack propagation has a relation to the characteristics of the substructures at the tip of the fatigue cracks.
3. While the rates of propagation are retarded by static pre-strains, they increase in proportion to the degree of substructure formation due to alternating stresses.
4. The rates are usually reduced by the recovery after alternating deformation.

On the basis of the above results, the significance of substructures for fatigue fracture is discussed.     

Evolution of the defect substructure in V-4Ti-4Cr alloy under severe plastic deformation

The evolution of the defect substructure in V-4Ti-4Cr alloy under its severe plastic deformation by torsion in Bridgman anvils is studied by transmission electron microscopy. Nanoband structural states with a dipole or multipole character of misorientations and a crystallite (or nanoband) size varying from several to several tens of nanometers form in the true logarithmic strain range e ≈ 3.0−6.6. Such crystallites form inside 100-nm submicrocrystallites or coalesce (at e ≥ 6) to yield mesobands with a pronounced vortex character of their propagation. The formation of these states is related to the activation (by the flows of nonequilibrium point defects in stress fields) of quasi-viscous deformation and lattice reorientation mechanisms, which provide the generation and propagation of partial disclination nanodipoles followed by the development of collective effects in a disclination substructure. These effects lead to the group motion of nanodipoles inside the mesobands.     

Influence of grain-boundary dynamics on shear and rotational deformation components in the creep of polycrystals

The as-a-whole motion of polycrystal grains with migrating and stationary boundaries is investigated during the creep of lead and lead-based alloys. It is shown that boundary migration promotes grain-boundary slip and fragmentation of regions along the boundaries, and that the effect is not related to differing orientations of the migrating and stationary boundaries. Migrating and stationary boundaries of equal slope were formed in aging alloys as a result of intermittent segregation and coalescence of phases. V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Tomsk Branch, Institute of Structural Macrokinetics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 40–45, June, 1998.     

Instability of the crystal lattice of CuPd alloy

The results of structural investigations (x-ray structural analysis, small-angle scattering and electron microscopy) of the B2→Al deformation phase transition and the kinetics of the recovery processes of deformed CuPd alloy are presented. It is established that the phase transition occurs in regions of local plastic deformation and the B2→Al deformation transition helps to enrich these regions with palladium. Tomsk State Architecture-Construction Academy. V. D. Kuznetsov Siberian Physico-Technical Institute, Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 93–102, March, 1997.     

Microstructure of Mo – 47% Re – 0.4% Zr alloys after rolling at room temperature. I. Anisotropy of microband structure and peculiarities of internal structure of microbands

The results of an electron microscopy investigation of microstructure of a Mo – 47% Re – 0.4% Zr alloy after rolling deformation (ε ≈ 90%) at room temperature are presented. A special focus is made on investigation of anisotropy of microband nanostructured states and high-energy defect substructures with high values of the crystal lattice curvature, dislocation density and local internal stresses. A disclination mechanism of reorientation as a mechanism of fragmentation of the internal microband structure is proposed.