Влияние процессов микросегрегации на формирование периодических примесных сверхструктур в бинарных сплавах

The influence of the trapping of mobile impurity atoms by immobile defects on superstructures is analyzed. Superstructures are formed as a result of solid-solid phase transitions like the directional crystallization. A capillary wave model was used for the analysis. It was shown that the conditions for the appearance of periodic superstructures are facilitated when the time of the diffusion jump of impurity atoms is much shorter than the characteristic time of their segregation at defects.

Diffusion of Light Elements in BCC, FCC and HCP Metals

The mechanisms of formation of activated states upon diffusion of impurity interstitial atoms in metals have been identified, which allows formulation of the theoretical criterion for reliability of corresponding experimental data. This criterion is valid for almost all experimental results gained using precise techniques for bcc, fcc, and hcp metals. In case of hydrogen, oxygen, and nitrogen, most adequate are the models of potential diffusion barrier that are based on the elasticity theory. For carbon and boron, a less energy-taking mechanism is realized which involves the electron system rearrangement in a crystal during the diffusion jump. The accuracy of the theoretical criterion is in line with the capacities of modern precision techniques.

A STOCHASTIC MODEL OF THE EVOLUTION DERIVED FROM ELASTIC VELOCITY PROCESS WITH MIXED DIFFUSION-JUMP CHARACTERISTICS

The phenomenon of phase space evolution is modeled by the diffusional change in particles directions that is interrupted by independent collisions. Transition densities of stochastic process defined by this dynamical evolution are equivalent to solutions of a particular Boltzmann integro-differential equation. The general construction of solutions of this equation is developed. Specific methods of calculations of transition densities are detailed for the small angle approximation of the Boltzmann equation.

Microscopic Diffusion Mechanism of Iron in FeAl Revisited by New Methods

ABSTRACTThe elementary diffusion jump of Fe atoms in the ordered intermetallic alloy FeAl is studied in a coordinated effort of atomistic experimental techniques, Monte Carlo simulation and abinitio electron theory. The experiment demands that the elementary diffusion jump is a jump into an antistructure site on the Al sublattice which is occupied for a much shorter time than the sites on the Fe sublattice. The diffusion path can be followed by Monte Carlo simulations which can perfectly explain the experiments. Since ab-initio theory yields a very low concentration of Al vacancies it is suggested that correlated jumps of two atoms prevent the creation of a fully developed Al vacancy.