Atomic mechanisms of the beginning of plastic deformation and failure initiation in nanoparticles of
b.c.c. transition metals are presented in this report. It is shown that strength level of nanoparticles of
b.c.c. transition metals is pre-determined by the lattice instability within the local region of the
crystal. At uniaxial tension even at low temperatures perfect crystal becomes unstable to shear
(„orthorhombic“ path), i.e. local shear instability is the main mechanism of stress relaxation in
nanoparticles of b.c.c. metals. Specific features of local instability of nanoparticle under hydrostatic
tension are considered. A model of the temperature dependence of strength is offered. It is shown
that nanoparticle strength decreases as square root function of temperature with temperature growth.
Just this is essential difference of the temperature dependence of nanoparticle strength from the
same for “ordinary” single- and polycrystals.
A concept of atomic mechanisms governing strength of nanosized defect-free crystals is presented. It is exhibited that these mechanisms consist in local instability of the lattice. Two main reasons for localization of instability in three-dimension (3D) crystals are analyzed, namely, (i) fluctuation of local stresses induced by thermal vibrations of atoms, and (ii) non-uniform distribution of local stresses caused by a surface tension. Based on this conception, explanations of both the temperature dependence of strength of 3D nanocrystals and scale effect are given. Ideas on the reasons for and regularities of change in strength at transition from 3D to 2D (graphene) and 1D (monatomic chain) crystals are represented. It is shown that dimensionality of crystal is one of the main factors governing strength of defect-free crystals. Experimental values of the strength of carbon monatomic chains are given, which times exceeds the strength of graphene and is the highest attainable level of strength in the world.
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