Studies of concentration and temperature dependencies of precipitation kinetics in iron-copper alloys using kinetic monte carlo and stochastic statistical simulations

The earlier-developed ab initio model and the kinetic Monte Carlo method (KMCM) are used to simulate precipitation in a number of iron-copper alloys with different copper concentrations x and temperatures T. The same simulations are also made using the improved version of the earlier-suggested stochastic statistical method (SSM). The results obtained enable us to make a number of general conclusions about the dependencies of the decomposition kinetics in Fe-Cu alloys on x and T. We also show that the SSM describes the precipitation kinetics in a fair agreement with the KMCM, and employing the SSM in conjunction with the KMCM enables us to extend the KMC simulations to the longer evolution times. The results of simulations seem to agree with available experimental data for Fe-Cu alloys within statistical errors of simulations and the scatter of experimental results. Comparison of results of simulations to experiments for some multicomponent Fe-Cu-based alloys enables us to make certain conclusions about the influence of alloying elements in these alloys on the precipitation kinetics at different stages of evolution.Comment: 18 pages, 17 postscript figures, LaTe

Peculiarities of phonon spectra and lattice heat capacity in Ir and Rh

A simple pseudopotential model is proposed, which allows the phonon spectra and temperature dependence of the lattice heat capacity of Ir and Rh be described with a high enough accuracy. A careful comparison of the calculated and experimental values of the lattice heat capacity is carried out, with the procedure of the identification of the phonon contribution to the heat capacity and determination of the characteristics (momenta) of the phonon density of states from the experimental values of the total heat capacity of metal at a constant pressure being described in detail. The results of the theoretical calculations explain, in particular, such peculiar feature of Ir and Rh, unusual for cubic metals, as a sharp (more than by a factor of 1.5) decrease in the effective Debye temperature with increasing termperature. The temperature dependence of the mean square amplitude of atomic displacements in Ir and Rh has been calculated. Basing on the band calculations the manifestation of the Kohn singularities in the phonon spectra of Ir are discussed.Comment: 15 pages, LaTeX2e, 12 figures in postscrip

Characteristic features of anharmonic effects in the lattice dynamics of fcc metals

The dispersion in the entire Brillouin zone and the temperature dependence (right up to the melting temperature) of the anharmonic frequency shift and phonon damping in a number of fcc metals is investigated on the basis of microscopic calculations. It is found that the anharmonic effects depend sharply on the wave vector in the directions $\Gamma$-X, X-W, and $\Gamma$-L and, in contrast to bcc metals, the magnitude of the effects is not due to the softness of the initial phonon spectrum. It is shown that the relative frequency shifts and the phonon damping near melting do not exceed 10-20%. The relative role of various anharmonic processes is examined, and the relation between the results obtained and existing experimental data is discussed.Comment: 4 pages, 5 figures, LaTe

Peculiarities of anharmonic lattice dynamics and thermodynamics of alkaline-earth metals

The calculations are performed for a broad range of the properties of Ca and Sr in the fcc and bcc phases. A detailed information on the magnitude and character of temperature dependence of anharmonic effects in the lattice dynamics over the entire Brillouin zone (frequency shifts and phonon damping, Gruneisen parameters) is given. A detailed comparison of the computational results for the heat capacity and thermal expansion with the experimental data is carried out; the theoretical results are in good agreement with the experiment.Comment: 16 pages, 19 Postscript figures, Revte

Направления повышения эффективности эксплуатации локомотивов

The article contains the analysis of statistics of locomotives’ operation and define main opportunities to increase its efficiency. The main objective of the study is to reveal factors influencing the increase in reliability of locomotives.Data of the sample of 40 locomotives of main series operated in Russia for the period of 400–500 days are used, which ensures accuracy of results obtained. The method of the study is mainly statistical processing of data. Besides commonly statistically analyzed positions like «in operation» and «faulty» new positions «at the head of the train» (effective work) and some other are considered. The coefficient of useful (effective) work is introduced. As a result, it is proved that feasible level of value-added use of locomotive up to 75 % of total time versus 49 % nowadays is possible. It is shown that reduction of time and cost of technical maintenance and repair of locomotives (TMR) is an important opportunity to increase efficiency of locomotives’ operation. Besides, it has been proved that one of the reasons of over-downtime of locomotives under repair is a significant volume of violations of operating modes, which is also confirmed by statistical data used in previous publications.В статье выполнен анализ статистики эксплуатации локомотивов и определены основные направления повышения эффективности тяги поездов. Основная цель исследования – выявление факторов повышения надёжности локомотивов.При этом использованы данные выборки по 40 локомотивам всех основных серий, эксплуатируемых в России, за 400–500 дней эксплуатации, что гарантирует достоверность полученных результатов. Метод исследования – статистическая обработка данных. При этом в дополнение к общепринятым состояниям «исправное» и «неисправное» рассмотрены новые «в голове поезда» (полезная работа) и ряд других. Введён коэффициент полезной работы. В результате доказан реально возможный уровень полезного использования локомотива до 75 % от общего времени против 49 % в настоящее время. Показано, что сокращение времени и стоимости технического обслуживания и ремонта локомотивов (ТОиР) является важным направлением повышения эффективности эксплуатации локомотивов. При этом ранее было показано, что одна из причин перепростоя локомотивов на ремонте – это существенный объём нарушений режимов эксплуатации, что было подтверждено статистическими данными