Bella A. Greenberg

A mechanism for the consolidation (performed experimentally earlier) of brittle quartz powder particles under a strong external action (high-pressure torsion) is proposed. This mechanism is based on possible destruction of silicon–oxygen tetrahedra via breakage of the Si–O interatomic bonds. The surface layer of the ceramic powder particles is shown to contain initial tetrahedra and their “fragments,” i.e., defects of the tetrahedra (proposed for the first time by the authors together with the name). The emergence of the tetrahedra and their fragments to the surface by the faces, edges, and vertices predetermines the surface shape and, eventually, surface adhesion. The enhancement of an external action results in healing broken Si–O bonds, which predetermines the possibility of partial or complete consolidation.

The paper studies the interface relief of copper–tantalum, copper–titanium and copper–copper joints. It demonstrates that interfaces could be considered as a fractal object. Fractal dimensions are calculated for these joints. A rule is established for the behavior of the fractal dimension during the transition from flat interfaces to wavy ones; this rule holds true of all joint pairs. Some behavior specifics are found for the fractal dimension of wavy interfaces of the copper–copper joint (which was substituted with Cu-Cu80Ni20 joint for convenience). The study shows that the fractal dimension in general decreases when welding modes are intensified. However, in the case of welding modes that are close in terms of energy input, certain peculiarities or deviations from such behavior can be observed. Graphical Abstract

The results of systematic field pneumatic tests of gas pipeline pipes of strength class K65(X80) are analyzed. The geometric and energy parameters of the extended fracture of pipes with a diameter of 1420 mm have been determined. The links between the extraction of the plastic strip at the fracture, the width of the strip and the fracture work (per running meter) have been confirmed. It is shown that along the rupture path, the work of A decreases several times along with a decrease in its velocity and gas pressure. Such adaptive destruction is caused by a change in the ratio of the proportion of slopes and flat areas in the slate fracture. The maximum work at the start of a crack is the energy consumption of pipe destruction. It is determined by the material constant, the hardening factor, determined by the ratio of the ultimate strength to the yield strength (σb / σ0.2). In existing gas pipelines made of pipes of strength class X80, the energy consumption reserve is higher than can be provided by experimental pipe steels of strength classes X100 and X120.

An analytical model of the elastoplastic stress-strain state of the material in the pre-fracture zone in front of the crack tip is proposed. It is shown that the error in estimating the maximum normal voltage in the specified zone is about 6% compared to the results of the finite element calculation.

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The paper studies the interface behavior of multi-layered Cu-Ta composites successfully produced by means of single-shot explosive welding technique. It is found that the transition zone may have three states at the same time: smooth interface, flat interface (consisting of individual cusps) and wavy interface also. The study shows the role of mutual solubility of initial elements in the formation of a welded joint structure. Based on electron microscopic studies, multi-layered composite is compared with two-layered Cu-Ta composites. Similarities of the interface microstructure elements and hardening behavior as well as reasons for the differences between them are discussed.

Self-organization processes that determine the response of a system to strong external influences are investigated. Explosion welding and torsion under pressure are selected as such...

Electron-microscopic studies of the processes of self-organization and evolution of the microstructure of metals and intermetallic compounds under different strong external actions are...

The evolution of the dislocation structure in the Ni3Ge intermetallic compound after high pressure torsion is investigated. The conditions for observing dislocation self-locking resulted...

The structural evolution of crystalline ceramics and amorphous glasses during high pressure torsion is analyzed. Enhanced consolidation of ceramic powders under high pressure torsion is...