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

THE INFLUENCE OF HYDROGEN ALLOYING ON THE STRUCTURE, PHASE COMPOSITION AND TECHNOLOGICAL PLASTICITY OF THE TITANIUM ALLOY WITH ALUMINUM CONTENT EXCEEDING LIMIT SOLUBILITYABSTRACT

Установлено влияние водорода на структуру, фазовый состав и сопротивление горячей пластической деформации опытного сплава Ti–8,7Al–1,5Zr–2Mo, перспективного для изготовления силовых режущих хирургических инструментов. Установлено, что легирование водородом до 0,3 и 0,6 масс. % увеличивает объемную долю β-фазы при температурах α+α2+β-области и снижает предел текучести сплава на 115–200 МПа при температурах деформации 800–850С.The influence of hydrogen on the structure, phase composition and resistance of hot plastic deformation of the Ti–8.7Al–1.5Zr–2Moexperimental alloy, promising for the manufacture of power cutting surgical instruments, is established. It was found that doping with hydrogen to 0.3 and 0.6 wt. % increases the volume fraction of the β-phase at temperatures α+α2+β-region and reduces the yield strength of the alloy by 115–200 MPa at deformation temperatures of 800–850°C

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

Basics of Bose-Einstein Condensation

The review is devoted to the elucidation of the basic problems arising in the theoretical investigation of systems with Bose-Einstein condensate. Understanding these challenging problems is necessary for the correct description of Bose-condensed systems. The principal problems considered in the review are as follows: (i) What is the relation between Bose-Einstein condensation and global gauge symmetry breaking? (ii) How to resolve the Hohenberg-Martin dilemma of conserving versus gapless theories? (iii) How to describe Bose-condensed systems in strong spatially random potentials? (iv) Whether thermodynamically anomalous fluctuations in Bose systems are admissible? (v) How to create nonground-state condensates? Detailed answers to these questions are given in the review. As examples of nonequilibrium condensates, three cases are described: coherent modes, turbulent superfluids, and heterophase fluids.Comment: Review articl