Phase Diagrams of Polytype Transformations in Close-Packed Crystals Including Metastable States

The paper offers a method for calculating phase diagrams of polytype transformations in close-packed crystals based on the generalized axial Ising's model of finite dimensions at non-zero temperatures. Using the Metropolis algorithm, the behavior of systems with polytype transitions is studied under the conditions of changing external shear stress and temperature. The longest polytype period considered here is taken to be 30 close-packed planes.     

Shear strength of metals behind shock fronts

Results are presented from a numerical modeling of experiments, conducted by J. Lipkin, R. Asay, L. Chabildas, and J. Wise, in which shock-compressed aluminum and polycrystalline beryllium were loaded again by shock waves. Reproduction of the experimental structures of the impulses in the calculations made it possible to determine the stresses acting in the materials during the primary and secondary shock loading, as well as to study the dynamics of the secondary shock load. It is shown that resistance to plastic strain is maintained in aluminum and beryllium behind the front of weak shock waves with intensities up to 10 GPa. The shear strength of the material behind the front does not correspond to the shear stresses at the Hugoniot elastic limit. For aluminum alloy 6061-T6 and beryllium, shear strength behind the fronts of shock waves with amplitudes up to 10 GPa is lower than in the elastic precursor but is greater than the static yield point of the material in the initial state.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 62–66, October, 1995.     

Rhombohedral superlattices based on bcc ones: Concentration and displacement waves

Superlattices based on bcc ones are considered that have space groups P 3ml or P3ml and tripled parameters in the initial cubic axes. Expressions are derived for the concentration and displacement waves corresponding to these superlattices.Translated from Izvestiya Vysshikh Uchebynkh Zavedenii, Fizika, No. 9, pp. 91–96, September, 1991.     

The behavior of crowdions and their complexes in weakly stable states of materials

Using the method of molecular dynamics, both single crowdions and their complexes are investigated in an fccmaterial being in a low-stability state with respect to an external thermal force. The system’s state with single crowdions is shown to be weakly stable, and their complexes therefore present a more favorable interstitial position. It is established that even under moderate external action (thermal activation or propagation of a standing wave) single crowdions form a dumbbell defect. In a low-stability state that is developed in the vicinity of structural-phase transformations, it is the crowdion complexes which represent more stable configurations. In addition, the bulk crowdion complex appears to be most favorable, being virtually unaffected by the phonon friction.     

Dynamic long-period nanosized states in lattice structure

Using a biatomic chain of atoms as an example, whose interaction was represented by the Morse potential, we revealed a possibility for a long-lived, dynamic, long-period, nanosized state to persist in the lattice structure. This nanosized structure (in the case in question, the length of the spatial period of energy localization was found to be 16–20 nm) is generated under excitation of a vibrational short-wave mode, with the atoms of the light component only participating. The resulting dynamic nanostructures are principally different in their nature and characteristics from those described earlier and developed via a mechanism of modulation instability of short-wave vibrational modes. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 21–26, February, 2009.