G. A. Malygin

Plasticity and strength of micro- and nanocrystalline materials

This review is devoted to the effect of grain boundaries on the deformational and strength properties of poly-, micro-, and nanocrystalline materials (predominantly metals). The main experimental facts and mechanisms concerning the dislocation structure and mechanical behavior of these materials over wide ranges of temperatures and grain sizes are presented. The experimentally established regularities are analyzed theoretically in terms of equations of dislocation kinetics taking into account the properties of grain boundaries as barriers, sources, and sinks for dislocations and as places where dislocations annihilate. The origin of the Hall-Petch relations for the yield stress and the flow stress as functions of the grain size, as well as the deviations from these relations observed in nano- and microcrystalline materials, is discussed in detail in terms of the dislocation-kinetics approach. Embrittlement of micro- and nanocrystalline materials at low temperatures and superplasticity of these materials at elevated temperatures are also analyzed in terms of the dislocation-kinetics approach.

Acoustoplastic effect and the stress superimposition mechanism

The mechanism of the acoustoplastic effect is discussed which arises when an oscillatory stress of an acoustic frequency is superimposed during quasi-static deformation of a crystal. The kinetics of the acoustoplastic effect and its dependence on the amount of plastic deformation, amplitude of acoustic-frequency stresses, temperature, and strain rate are investigated in terms of the stress superimposition mechanism by a computer simulation method.

On the power-law pressure dependence of the plastic strain rate of crystals under intense shock wave loading

The plastic deformation of metallic crystals under intense shock wave loading has been theoretically investigated. It has been experimentally found that the plastic strain rate

Analysis of the strain-rate sensitivity of flow stresses in nanocrystalline FCC and BCC metals

\dot \varepsilon

Structure factors that influence the stability of plastic strain of bcc metals under tensile load

and the pressure in the wave P are related by the empirical expression

Nanoscopic size effects on martensitic transformations in shape memory alloys

\dot \varepsilon

Influence of the transverse size of samples with micro- and nano-grained structures on the yield and flow stresses

∼ P4 (the Swegle-Grady law). The performed dislocation-kinetic analysis of the mechanism of the origin of this relationship has revealed that its power-law character is determined by the power-law pressure dependence of the density of geometrically necessary dislocations generated at the shock wave front ρ ∼ P3. In combination with the rate of viscous motion of dislocations, which varies linearly with pressure (u ∼ P), this leads to the experimentally observed relationship

Kinetic mechanism of the formation of fragmented dislocation structures upon large plastic deformations

\dot \varepsilon

Size effects under martensitic deformation of shape-memory alloys

∼ P4 for a wide variety of materials with different types of crystal lattices in accordance with the Orowan relationship for the plastic strain rate

Size effects under plastic deformation of microcrystals and nanocrystals

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