Plastic deformation of ultrafine-grained metallic materials

Abstract

The micromechanisms of plastic deformation of ultrafine grained metallic materials are analyzed using copper, the nanostructure of which is produced by equal channel angular pressing, as an example. Slip traces are studied at various deformation stages, and their parameters are estimated. The change in the gran ular structure during deformation has been studied.

Self-Similar Mode of Metals Fragmentation under Severe Plastic Deformation

“…In formulas (1)-(4), 0 is a part of the internal energy that does not depend on the imperfection in the material structure (the reference level); ℎ and ℎ are the GB and dislocation densities, respectively 1 ; the subscript values = and = denote the GBs and dislocations, respectively; = + 2 is the modulus of uniaxial compression of a material [26,27]; and are the Lamé constants; and 2 ≡ (− + )/2 are the first and second, respectively, invariants of the elastic strain tensor; * 0 is the characteristic defect energy involving the defect dimensionality (per unit length for dislocations and per unit surface area for GBs); 0 is an analog of * 0 taking the influence of elastic deformations in the linear (the constant ) and quadratic approximations into account; the positive constant is responsible for either the generation of structural defects at stretching ( > 0) or their annihilation at compression ( < 0);¯and¯are elastic constants that reflect the decrease of corresponding elastic moduli owing to the presence of structural defects; 1 and * 1 are coefficients that are responsible for the recrystallization (defect annihilation) considering and not considering, respectively, the influence of an elastic deformation in the linear approximation (constant ); accordingly, the parameter characterizes the enhancement of the annihilation process at > 0 (in the case < 0, the backward process is implied); and is a parameter that characterizes the interaction energy of selected structural defects. In the general case, the positive terms in relation (1) are responsible for the generation of structural defects, and the negative terms correspond to the inverse processes, the defect annihilation (recrystallization).…”

“…The first ones are large-angle, or geometrically necessary, boundaries, which arise as a result of various activities of the sliding system around the GBs. The second ones are the boundaries or subboundaries of cells, which are often called random dislocation boundaries, because they arise at the mutual implementation of a statically random dislocation intersection inside the grains [27,29]. The boundaries between arbitrarily arranged grains are much more mobile than the latter.…”

“…Hence, the self-similar character of the metal structure evolution is realized by activating the self-organized processes of various kinds, which arise as a result of the noise inherent to main parameters. It is known that it is the interaction of structural defects with one another and with defects of other structural levels-in our case, this is the interaction of GBs with dislocations, other boundaries, and structural inhomogeneities, such as structural defects of other levels, thermal fluctuations, thermodynamical phases of the substance, impurities, vacancies, and so forth-that leads to the manifestation of internal fluctuations and the changes in grain misorientations in the granular structure of a metal specimen [1,27,29,39,40]. As a result, the emerged boundary structure contains crystallites with a specific structure.…”

Influence of the Grain Size on the Dispersion Strengthening of VT1-0 Alloy Implanted with Aluminum Ions

“…It has been established by now that the strength of any metal material is determined by numerous factors [1], one of which is the presence of carbide and oxide particles and other secondary phases in the material. It is also known that the number of present particles, their size, distribution pattern and interparticle distance, as well as the irregularity degree of the matrix lattice and precipitation have an effect on the material dispersion strengthening [2].…”