A. G. Kadomtsev

Evolution of microscopic cracks and pores in solids under loading

Experimental data on the development and partial healing of microscopic cracks and pores in loaded crystalline materials are considered. An analysis of the data indicates that fracture development has a number of specific features depending on the state of the materials and the testing conditions and is a kinetic thermal fluctuation process occurring virtually throughout the entire time of loading.

Excess free volume and mechanical properties of amorphous alloys

Characteristics of the excess free volume in amorphous alloys quenched from a melt are investigated and analyzed. It is established by small-angle x-ray scattering that the application of intense hydrostatic pressure causes this volume to decrease. This decrease leads to an enhancement of a number of characteristics of the mechanical properties of amorphous alloys.

Mechanical properties and structural features of nanocrystalline titanium produced by cryorolling

A broad spectrum of physicomechanical properties of the VT1-0 nanocrystalline titanium produced by cryomechanical fragmentation of the grain structure using rolling at a temperature close to liquid-nitrogen temperature has been studied. It has been found that the mechanism of grain refinement is associated with grain fragmentation by twins. Exactly the twin nature of internal interfaces (crystallite boundaries) provides the thermal and structural stability of nanocrystalline titanium produced by cryomechanical grain fragmentation in the temperature range to ∼500 K. It has been assumed that the observed decrease in the titanium density due to cryorolling is associated with a number of factors (high density of introduced dislocations, nanopore formation, and changes in titanium lattice parameters).

Influence of the number of passes under equal-channel angular pressing on the elastic-plastic properties, durability, and defect structure of the Al + 0.2 wt % Sc alloy

The regularities of the influence of the number of passes under equal-channel angular pressing on the mechanical properties and defect structure of an aluminum alloy have been elucidated. It has been established that the degradation of the mechanical properties (a decrease in the durability) is associated with the formation of nanoregions of an excess free volume in the course of severe plastic deformation under equalchannel angular pressing. A correlation between the nucleation of excess free volume regions and the formation of high-angle grain boundaries under equal-channel angular pressing has been revealed. The nature of the influence of severe plastic deformation on the elastic modulus, the vibration decrement, and the microplastic flow stress has been analyzed.

Nanoporosity of Fine-Crystalline Aluminum and an Aluminum-Based Alloy

The presence of nanopores formed during the equal-channel angular pressing of aluminum is revealed using small-angle x-ray scattering. The parameters of nanopores are determined, and a correlation between the level of nanoporosity and the fraction of high-angle grain boundaries is found. The data obtained indicate that the level of nanoporosity can affect the tensile durability of fine-crystalline aluminum in the creep mode. The data on the regularities in the development of nanopores under deformation of the fine-crystalline aluminum-based alloy in the superplasticity mode are obtained.

Mechanical properties, density, and defect structure of VT1-0 titanium after intense plastic deformation due to screw and longitudinal rollings

The influence of screw rolling combined with standard methods of mechanothermal treatment on the homogeneity of the forming submicrocrystalline structure, density, and mechanical performance of VT1-0 commercial titanium is studied. It is shown that such a treatment carried out within optimal temperature and strain rate intervals (special deformation conditions) causes minor softening of the material and can be effectively used to form a homogeneous submicrocrystalline structure with high strength and elastoplastic properties.

Fracture features of granite under various deformation conditions

Fracture mechanisms of dry and water-saturated granite samples and slip (displacement) along a ready fault have been studied by measuring acoustic emission signals. It has been found that disperse defect formation is observed in dry samples under mechanical load, then localization occurs, and a fracture source is formed, whose development results in macrofault formation. In water saturated samples, chaotic defect formation occurs in the entire volume, which leads to a high degree of material damage. At the closing deformation stage, several fault source zones are formed in which main cracks develop. In the case of slip along a ready fault, stoppers at crack edges are broken.

Elasticity and anelasticity of microcrystalline aluminum samples having various deformation and thermal histories

The effect of the amplitude of vibrational deformation on the elastic modulus and internal friction of microcrystalline aluminum samples produced by equal-channel angular pressing was studied. The samples have various deformation and thermal histories. The elastic and inelastic (microplastic) properties of the samples are investigated. As the degree of plastic deformation increases, the Young’s modulus E, the amplitude-independent decrement δi, and the microplastic flow stress σ increase. As the annealing temperature increases, the quantities δi and σ decrease noticeably and the modulus E exhibits a more complex behavior. The experimental data are discussed under the assumption that the dislocation mobility depends on both the spectrum of point defects and the internal stresses, whose level is determined by the degree of plastic deformation and the temperature of subsequent annealing. The concept of internal stresses is also used to analyze the data on the effect of the degree of deformation and annealing on the rupture strength of the samples.

Effect of a defect structure on the static and long-term strength of submicrocrystalline VT1-0 titanium fabricated by plastic deformation during screw and lengthwise rolling

The effect of nanoporosity and the highly dispersed carbide particles that form during screw and lengthwise rolling of VT1-0 titanium on its mechanical and, partly, thermal stability characteristics is revealed and analyzed.

Durability and static strength of microcrystalline titanium VT1-0 obtained by equal-channel angular pressing

The influence of deformation by equal-channel angular pressing (ECAP) on the durability of titanium (VT1-0 grade) tensile tested under creep conditions has been studied for the first time. It is established that the ECAP-induced transition of titanium to a microcrystalline state leads to a decrease in the durability, while the characteristics of static strength are improved.