Abstract: Junction disclinations are important elements of the structure of nanostructured metals
produced by severe plastic deformation (SPD). Effect of these defects on the formation energy of
vacancies in grain boundaries (GBs) is studied by means of atomistic computer simulations.
Estimates based on the calculations of vacancy formation energies suggest that at least two orders of
magnitude increase of the GB diffusion coefficient can be expected due to junction disclinations in
Abstract: The following experimental data are presented and discussed: a) the explosion-like
nucleation of micro- (meso) cracks; b) the dependence of the scale of local “microcatastrophe” on
the relation between the released strain energy and the dissipative properties of the nearest
environment; c) the determinative influence of the dissipative properties on the rate of redistribution
of local stresses. The presented data evidence that every event of defect nucleation that takes place
at either micro- or mesoscale level in the heterogeneous solid examines the energy absorbtion
properties of the whole system. Future localization of the macroscopical failure is of “accidental
type”, that is results from random, active formation of the ensemble of micro- and mesocracks in
different localities as a consequence of the decrease of the dissipative capability of surrounding
Abstract: The advantages of the OMI algorithm to compute the logarithmic decrement and the
resonant frequency from free decaying oscillations is reported. The OMI algorithm is proved to be
the best solution in the computation of the logarithmic decrement and the resonant frequency for
high damping levels.
Abstract: Internal friction peaks observed in single or polycrystals are clearly due to a dislocation
relaxation mechanism. Because a sample observed by transmission electron microscopy (TEM)
often exhibits in the same time various dislocation microstructures (isolated dislocations,
dislocation walls, etc.) it is very difficult to connect the observed relaxation peak with a particular
dislocation microstructure. Using isothermal mechanical spectroscopy (IMS), it is easier to
compare, for instance, the evolution of a relaxation peak with measurement temperature to the
microstructural evolution observed by in-situ TEM at the same temperatures. IMS was used to
study a relaxation peak in a 5N aluminium single crystal firstly 1% cold worked and then annealed
at various temperatures. TEM experiments performed in the same material at various temperatures
equal to the temperatures used for the damping experiments made possible to link this internal
friction peak with a relaxation effect occurring inside dislocation walls. In two other experiments in
a 4N aluminium polycrystal and in a metal matrix composite with SiC whiskers, it is shown that the
observed relaxation peaks are connected to the motion of dislocations inside polygonization
boundaries in the first case and in dislocation pile-ups around each whisker in the second one.
Theoretical models proposed to explain such relaxation peaks due to a dislocation motion inside a
dislocation wall or network are discussed.
Abstract: High temperature plasticity of fine-grained ceramics (ZrO2, Al2O3, etc) is usually
associated with a grain boundary sliding process. The aim of the present research is then to improve
the high-temperature mechanical strength of polycrystalline zirconia (3Y-TZP) through the
insertion of multiwalled carbon nanotubes (CNTs) or silicon carbide whiskers (SiCw), which are
susceptible to pin the grain boundaries. The effect of these nano-sized particles on grain boundary
sliding has been studied by mechanical spectroscopy.
Abstract: An influence of Cd content on the kinetics of a spontaneous low-temperature structure
transformation in In-rich In - Cd alloys has been investigated using acoustic, resistivity and DSCtechniques.
It is established that increase of the concentration of Cd leads to an essential increase of
a driving force of the transition that results in an increase of the transition rate and in decrease of the
relaxation time. The low-temperature instability of acoustic, resistivity and thermal properties is
caused presumably by a decomposition of the solid solution that has features of a phase transition of
the 1st order. The main empirical activation parameters of the transformation are derived. The
activation energy amounts to U0 = 0.43 eV, the attempt period is τ 0 =5 × 10-9 s. The probable border
of the decomposition in the phase diagram of the In-Cd system is established.
Abstract: Acoustic properties of polycrystalline Cr samples of 99.99 % purity are investigated at
frequencies of longitudinal vibrations f ~ 75 kHz and of bending vibrations at 0.6 < f < 1.5 kHz
when thermocycling within the temperature interval 5 − 330 K. Special attention is paid to the
acoustic anomalies in the vicinity of the magnetic phase transitions: the Néel point and the spin-flip
transition. In the as-received samples, a significant hysteresis of the acoustic properties has been
found for the first time. The effect of heat treatments on internal friction and elastic properties of
chromium polycrystals is also investigated. The data obtained are compared with the effect of small
preliminary deformation and а long-time ageing at room temperature on the ultrasound anomalies in
Cr single crystal. The observed behavior of the acoustic properties may be caused by changes in the
antiferromagnetic domain structure in Cr polycrystals under the action of thermoelastic stresses
arising from quenching, preliminary plastic deformation or thermocycling.