Nonclassical rotational behavior at the vicinity of the lamda point

The rotational property of a quantum liquid at the vicinity of the lambda point is examined. In a liquid helium 4 just above the lambda point, under the strong influence of Bose statistics, the coherent many-body wave function grows to an intermediate size between a macroscopic and a microscopic one, which is of a different nature from the thermal fluctuations. It must reflect in the rotational properties such as the moment of inertia. Beginning with the bosons without the condensate, we make a perturbation calculation of its susceptibility with respect to the repulsive interaction, and examine how, with decreasing temperature, the growth of the coherent wave function gradually changes the rotational behavior of a liquid:The moment of inertia slightly decreases just above the lambda point. This means that at the vicinity of the lambda point, the mechanical superfluid density does not always agree with the thermodynamical one.We compare the result to the experiment by Hess and Fairbank. A new interpretation of the shear viscosity just above the lambda point is given from this viewpoint.Comment: 12pages, 5figure

Stages of steady diffusion growth of a gas bubble in strongly supersaturated gas-liquid solution

Gas bubble growth as a result of diffusion flux of dissolved gas molecules from the surrounding supersaturated solution to the bubble surface is studied. The condition of the flux steadiness is revealed. A limitation from below on the bubble radius is considered. Its fulfillment guarantees the smallness of fluctuation influence on bubble growth and irreversibility of this process. Under the conditions of steadiness of diffusion flux three stages of bubble growth are marked out. With account for Laplace forces in the bubble intervals of bubble size change and time intervals of these stages are found. The trend of the third stage towards the self-similar regime of the bubble growth, when Laplace forces in the bubble are completely neglected, is described analytically.Comment: 22 page

Multichannel Approach to Clustering Matter

An approach is developed, combining the ideas of quantum statistical mechanics and multichannel theory of scattering, for treating statistical systems whose constituents can possess different bound states realized as compact clusters. The main principles for constructing multichannel cluster Hamiltonians are formulated: principle of statistical correctness, principle of cluster coexistence, and principle of potential scaling. The importance of the principle of statistical correctness is emphasized by showing that when it does not hold the behaviour of thermodynamic functions becomes essentially distorted. And moreover, unphysical instabilities can appear. The ideas are carefully illustrated by a statistical model of hot nuclear matter.Comment: 1 file, LaTex, no figure

Homogeneous bubble nucleation limit of lead

Liquid heavy metal coolant in a fast reactor, as well as in accelerator driven systems, is exhibited to large thermal and pressure shocks which can cause cavitation in the coolant. Here we calculated the work of the critical bubble formation in the lead coolant and the nucleation rate in terms of the generalized Gibbs approach. It is demonstrated that such approach provides a more adequate description of the process of bubble nucleation as compared with the classical nucleation theory.Теплоносители на основе жидких тяжелых металлов в быстрых реакторах и реакторах, управляемых ускорителем, подвержены значительным тепловым и гидравлическим ударам, что может приводить к кавитации теплоносителя. Рассчитаны работа образования критических пузырьков в свинцовом теплоносителе и скорость их зарождения в рамках обобщенного подхода Гиббса. Показано, что такой подход обеспечивает более адекватное описание процесса зарождения пузырьков по сравнению с классической теорией нуклеации.Теплоносії на основі рідких важких металів у швидких реакторах і реакторах, керованих прискорювачем, схильні до значних теплових і гідравлічних ударів, що може призводити до кавітації теплоносія. Розраховані робота утворення критичних пухирців в свинцевому теплоносії та швидкість їх зародження в рамках узагальненого підходу Гіббса. Показано, що такий підхід забезпечує більш адекватний опис процесу зародження пухирців в порівнянні з класичною теорією нуклеації

Theory of the nonsteady diffusion growth of a gas bubble in a supersaturated solution of gas in liquid

Using a self-similar approach a general nonsteady theory is elaborated for the case of the diffusion growth of a gas bubble in a supersaturated solution of gas in liquid. Due to the fact that the solution and the bubble in it are physically isolated, the self-similar approach accounts for the balance of the number of gas molecules in the solution and in the bubble that expells incompressible liquid solvent while growing. The rate of growth of the bubble radius in its dependence from gas solubility and solution supersaturation is obtained. There is a nonsteady effect of rapid increase of the rate of bubble growth simultaneous with the growth of the product of gas solubility and solution supersaturation. This product is supplied with a limitation from above, which also stipulates isothermal conditions of bubble growth. The smallness of gas solubility is not presupposed.Comment: 22 pages, 3 figure

Self-similar solution of a nonsteady problem of nonisothermal vapour condensation on a droplet growing in diffusion regime

This paper presents a mathematically exact self-similar solution to the joint nonsteady problems of vapour diffusion towards a droplet growing in a vapour-gas medium and of removal of heat released by a droplet into a vapour-gas medium during vapour condensation. An equation for the temperature of the droplet is obtained; and it is only at that temperature that the self-similar solution exists. This equation requires the constancy of the droplet temperature and even defines it unambiguously throughout the whole period of the droplet growth. In the case of strong display of heat effects, when the droplet growth rate decreases significantly, the equation for the temperature of the droplet is solved analytically. It is shown that the obtained temperature fully coincides with the one that settles in the droplet simultaneously with the settlement of its diffusion regime of growth. At the obtained temperature of the droplet the interrelated nonsteady vapour concentration and temperature profiles of the vapour-gas medium around the droplet are expressed in terms of initial (prior to the nucleation of the droplet) parameters of the vapour-gas medium. The same parameters are used to formulate the law in accordance with which the droplet is growing in diffusion regime, and also to define the time that passes after the nucleation of the droplet till the settlement of diffusion regime of droplet growth, when the squared radius of the droplet becomes proportionate to time. For the sake of completeness the case of weak display of heat effects is been studied.Comment: 12 pages, 4 figure

THE FORMATION, STRUCTURE AND TEXTURE OF HIGH MODULUS TITANIUM ALLOY DURING HOT PLASTIC DEFORMATION

The regularities of the formation of the phase composition and structure of the experimental high-modulus titanium alloy Ti–8,7Al–1,5Zr–2,0Mo at hydrogen doping to different concentrations and subsequent precipitation of samples are analyzed. It was found that hydrogen leads to a decrease in the yield strength and stresses of the alloy flow at deformation temperatures of 800 and 850 °C. It is shown that hydrogen doping significantly affects the nature and intensity of the crystallographic texture formed during hot plastic deformation.Проанализированы закономерности формирования фазового состава и структуры опытного высокомодульного титанового сплава Ti–8,7Al–1,5Zr–2,0Mo при легировании водородом до различных концентраций и последующей осадке образцов. Установлено, что водород приводит к снижению предела текучести и напряжений течения сплава при температурах деформации 800 и 850 °С. Показано, что легирование водородом существенно влияет на характер и интенсивность кристаллографической текстуры, формирующейся при горячей пластической деформации

Structure and Texture Formation behaviour in Two-Phase Titanium Alloys Billets Obtained by Additive Manufacturing

Работа выполнена с применением оборудования ресурсного центра коллективного пользования «Авиационно-космические материалы и технологии» МАИ.The effect of heat treatment on the structure, mechanical properties and texture of titanium alloy Ti–6Al–4V billets, obtained by additive manufacturing technology was investigated in this work.В рамках проведенного исследования было изучено влияние термической обработки на структуру, механические свойства и текстуру заготовок из титанового сплава ВТ6, полученных при помощи аддитивной технологии прямого лазерного нанесения материала

УПРАВЛЕНИЕ ФАЗОВЫМ СОСТАВОМ, СТРУКТУРОЙ И КОМПЛЕКСОМ СВОЙСТВ ВЫСОКОМОДУЛЬНОГО ТИТАНОВОГО СПЛАВА МЕТОДАМИ ТЕРМОВОДОРОДНОЙ ОБРАБОТКИ

This paper considers the possibility and efficiency of thermohydrogen processing of the high-modulus Ti–8,7Al–1,5Zr–2,0Mo titanium alloy with aluminum content exceeding its solubility limit in α-titanium. Experimental data on the effect of hydrogen on the alloy phase composition and structure are obtained. Regularities of phase transformations in the hydrogen-containing alloy are analyzed under different thermal effects. An alloy–hydrogen system is diagramed in the hydrogen concentration range from the initial content up to 1,0 wt.% and temperature range from 20 up to 1100 °C. It is shown that a β single-phase structure forms in the alloy via quenching from the temperatures of β range at a hydrogen content of 0,6 wt.% or more. Hydrogen saturation up to 0,8–1,0 wt.% causes β → δ hydride shear transformation during quenching from the temperatures below 750 °C and results in partial eutectoidal β phase transformation at slow cooling. It is stated that hydrogen extends the region of β phase stability by decreasing the temperature of β / (α + β) transition by 210 °C (at 1,0 wt.% of hydrogen) and increases the temperature of α2 phase stability by 50 °C. Technological schemes and modes of thermohydrogen processing are developed and tested using the alloy specimens in order to form the two types of structure – submicrocrystalline and bimodal, and formation mechanisms of these structures under thermohydrogen processing are analyzed as well. Mechanical properties of the alloy specimens are determined. It is stated that thermohydrogen processing results in growth of strength and hardness as compared with the initial state. The thermohydrogen processing forming submicrocrystalline structure leads to decrease of plasticity characteristics at maximum hardness.Рассмотрены возможность и эффективность применения термоводородной обработки (ТВО) высокомодульного титанового сплава Ti–8,7Al–1,5Zr–2,0Mo с содержанием алюминия, превышающим предельную растворимость в α-титане. Получены экспериментальные данные о влиянии водорода на фазовый состав и структуру сплава. Проанализированы закономерности фазовых превращений в водородсодержащем сплаве при различных термических воздействиях. Построена фазовая диаграмма системы сплав–водород в интервале концентраций водорода от исходной до 1,0 мас.% и температур от 20 до 1100 °С. Показано, что при концентрации введенного водорода 0,6 % и более закалкой из β-области фиксируется однофазная β-структура. Насыщение водородом до 0,8–1,0 % приводит к реализации сдвигового гидридного β → δ-превращения при закалке с температур ниже 750 °С, а при медленном охлаждении – к частичному эвтектоидному превращению β-фазы. Установлено, что водород расширяет область стабильности β-фазы, снижая температуру β / α + β-перехода на 210 °С (при 1,0 % H), и повышает температуру устойчивости α2-фазы на 50 °С. Разработаны и опробованы на образцах сплава технологические схемы и режимы ТВО, формирующие два типа структур – субмикрокристаллическую и бимодальную. Проанализированы механизмы образования этих структур в процессе ТВО. Определены механические свойства образцов сплава. Установлено, что ТВО приводит к увеличению прочности и твердости по сравнению с исходным состоянием. Термоводородная обработка, формирующая микрокристаллическую структуру, обуславливает снижение характеристик пластичности при максимальной твердости