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.     

Special features of polytype transformations under changing external shear stress and temperature

Within the generalized axial finite-dimensional Ising model, possible model and experimental non-equilibrium polytype 3C-2H and 9R-3C transformations and twinning of the fcc-lattice of close-packed model crystals are considered. These transformations are realized in a great number of metals as well as cobalt, iron, and copper-base alloys and observed on variation of both the applied load and the temperature. The structure transformations simulated in the model may involve a number of multilayer metastable structures. Hysteresis phenomena found under variations of the external stress and temperature and their behavior in response to long-range interactions corresponding to atomic interactions in the fcc lattice in ten coordination spheres and in many-body interaction responsible for the stability of the 4H structure are considered. Factors accounting for the formation of metastable states and hysteresis effects are analyzed. It is shown that the crystal form may undergo a non-monotonic change as the applied load and temperature are varied. Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 80–86, September 1999.     

Model of a martensitic transformation of a two-dimensional crystal

A model of a configuration transition is proposed which describes the characteristic features of the martensitic transformation of a two-dimensional crystal. Such transformations are observed in certain microorganisms.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 80–84, February, 1992.     

Phase transitions in 1-D magnetic materials

Ferromagnetic ↔ antiferromagnetic phase transitions for one-dimensional systems are investigated using the Monte Carlo technique. Ground state diagrams are constructed within the framework of the Ising model. Using the Metropolis algorithm, the effects of external magnetic field and temperature variations on phase transitions are examined. Kinetic features of these transitions are included into consideration. It is shown that the correlational length coefficient v for ferromagnetic materials decreases with increase in the external magnetic field strength, while for antiferromagnetic this dependence is reverse. Behavior of the critical dynamic coefficient z under field variations for small one-dimensional magnetic is similar to that of coefficient v. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp.54–58, March, 2006.     

Behavior of Polytype Structures in Poor-Stability Systems under Varying External Loading

An approach to investigating polytype transformations in close-packed crystals based on the generalized axial finite-dimensional Ising model is proposed. Within this approach, an analysis is made of the influence that model dimensions and long-range and many-body interactions exert on the stability of short-period and multi-layer structures and the sequence of polytype transformations. Using computer simulation techniques, the potential behavior of systems with polytype transformations is studied by varying the external shear stress and temperature under equilibrium and nonequilibrium conditions. The results obtained agree with the experimental data. This approach furnishes a means for predicting new multi-layer polytype structures and determining their symmetry.     

Effect of grain-boundary conditions on polytype transformations in close-packed crystals

Within the framework of a modified Ising model, the effect of the boundary conditions (“free ends” and periodic boundary conditions) on the polytype structure stability is studied in close-packed crystals. Using the ground state diagrams, feasible structures and transformation induced by an external field are identified. An analysis of the model system dimensions and long- and short-range many-body interaction on the shape of the ground state diagrams under different boundary conditions is made. The temperature effects on the polytype structure characteristics are discussed in detail. It is shown that both at the absolute zero and finite temperatures, the effects of the boundary conditions on certain properties could be predominant.__________This revised version was published online in May 2005 with a correction on affiliation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 61–66, November 2004.