High pressure sintering of TiB2 ceramics at different temperatures

In this paper the effect of high-pressure sintering (HPS) temperature on the microstructure, physical and mechanical properties of TiB2 ceramics has been investigated. Initial TiB2 powder with the average particle size of 5 μm was sintered in a modifi ed high-pressure anvil-type apparatus under static pressure of 4 GPa in the temperature range of 1400–1800°C. It is shown that HPS allows preparing full-dense TiB2 ceramics with fi ne-grained structure. The density of samples rises with increasing the sintering temperature up to 1800°C while the maximal microhardness is observed on samples prepared in the temperature range of 1500–1600°C. XRD analysis has shown that this fact is connected with an increase of the level of internal stresses in these samples

СТРУКТУРА БЫСТРОЗАКАЛЕННЫХ ЛЕНТ ПОСЛЕ ЕСТЕСТВЕННОГО СТАРЕНИЯ

Alloy solidification at high cooling rates leads to significant changes in structure and phase composition. Conditions appear for a significant extension of solid solubility, grain refining, and formation of metastable phases or amorphous state. Due to this it is possible to obtain  unique combinations of physical, mechanical and other properties in rapidly quenched alloys. Undoubted scientific and practical interest is an application of  quenching processes from a liquid state for aluminum alloys with the purpose to improve their physical and mechanical properties.As the structure of such alloys is extremely unstable from a thermodynamic point of view the important issue is to study  temporal stability of the microstructure and phase composition of rapidly quenched aluminium alloys of various chemical composition. The paper has investigated an influence of various alloying elements on the structure, phase composition and durometric properties of aluminum foils obtained by liquid aluminum alloy melt-spinning on the disk rotating with various speed. Optical and electron microscopy  has been used to study structure and phase composition as well as X-ray structural analysis. It has been shown that alloying of aluminium with copper leads to an increase in micro-hardness up to 130–160 HV0.01, and alloying with chromium and zirconium provides micro-hardness up to 60–80 HV0.01. It has been shown that increasing in amount of alloying additions in the aluminum melt (Al–Cu system alloy) rises the number of CuAl2 precipitates and is accompanied with an increase in micro-hardness of aluminum foils. An increase in cooling rate of the aluminum melt (Al–Cr–Zr system) is accompanied with structure dispersion which increases micro-hardness of the casted foils. The obtained results have made it possible to establish the optimal percentage of alloying elements and the disk rotation speed providing the highest level of aluminium foils’ durometric properties.Затвердевание сплавов при высоких скоростях охлаждения приводит к существенным изменениям структуры и фазового состава. Появляются условия для значительного расширения области твердой растворимости, существенного измельчения зерна, формирования метастабильных фаз или аморфного состояния. Как результат, в быстрозакаленных сплавах можно получить уникальные сочетания физико-механических и других свойств. несомненный научный и практический интерес представляет собой применение процессов закалки из жидкого состояния для алюминиевых сплавов с целью повышения их физико-механических свойств.Поскольку структура таких сплавов крайне нестабильна с термодинамической точки зрения, то важным моментом является изучение временной стабильности микроструктуры и фазового состава быстрозакаленных алюминиевых сплавов различного химического состава. Исследовано влияние различных легирующих элементов на структуру, фазовый состав и дюрометрические характеристики алюминиевых фольг, полученных путем разливки жидкого алюминиевого сплава на диск, вращающийся с различной скоростью. Для изучения структуры и фазового состава использовали оптическую и электронную микроскопию, а также рентгеноструктурный анализ. Показано, что легирование алюминия медью приводит к увеличению его микротвердости до 130–160 HV0,01, а при легировании хромом и цирконием – до 60–80 HV0,01, а повышение количества легирующих составляющих в расплаве на основе алюминия (сплав системы Al–Cu) приводит к росту количества выделившихся частиц CuAl2 и сопровождается увеличением микротвердости алюминиевых фольг. Увеличение скорости охлаждения алюминиевого расплава системы Al–Cr–Zr сопровождается диспергированием структуры, что приводит к возрастанию микротвердости получаемых фольг. На основании полученных результатов выбраны оптимальное процентное содержание легирующих добавок и скорость вращения диска, обеспечивающие наиболее высокие дюрометрические свойства алюминиевых фольг

Влияние скорости нагрева цементируемых конструкционных сталей на рост аустенитного зерна в процессе высокотемпературной выдержки

The influence of the heating mode of samples of constructional cemented steels 20ХН3А, 20ХГНР and 15ХГН2ТА on the value of austenite grain after high-temperature isothermal aging at 1000 °С is studied. It is shown that the heating of steels at a rate of 1.2–3.0 °C / min in the phase-transformation interval stabilizes the grain structure of the steels and leads to a slowing down of the kinetics of the growth of austenite grains during prolonged high-temperature aging, which makes it possible to increase the temperature of the chemical-thermal treatment of steels. It is concluded that the stabilization of the grain structure of steels is associated with the formation of segregation of impurity atoms and particles at grain boundaries with high-angle disorientation during slow heating, which prevents migration of grain boundaries in the process of prolonged high-temperature aging. A high-temperature chemical-thermal treatment of a batch of billets from steel 20ХН3А under experimental conditions with stepwise heating in the phase-transformation interval provided a qualitative fine-grained structure of the cemented layer.Исследовано влияние режима нагрева образцов конструкционных цементируемых сталей 20ХН3А, 20ХГНР и 15ХГН2ТА на величину аустенитного зерна после высокотемпературной изотермической выдержки при 1000 °С. Показано, что нагрев сталей со скоростью 1,2–3,0 °С/мин в интервале фазового α→γ превращения стабилизирует зеренную структуру сталей и приводит к замедлению кинетики роста аустенитного зерна при длительной высокотемпературной выдержке, что позволяет повысить температуру химико-термической обработки сталей. Сделано заключение, что стабилизация зеренной структуры сталей связана с образованием при медленном нагреве сегрегаций примесных атомов и частиц на границах зерен с высокоугловой разориентацией, что препятствует миграции границ зерен в процессе длительной высокотемпературной выдержки. Проведена высокотемпературная химико-термическая обработка партии заготовок из стали 20ХН3А по экспериментальному режиму со ступенчатым нагревом в интервале фазового α→γ превращения, обеспечившему получение качественной мелкозернистой структуры цементированного слоя

Механические свойства и структурное состояние покрытий Cr–N и Ti–Cr–N, сформированных методом вакуумно-дугового осаждения

With the development of nuclear industry, the requirements for materials capable of operating under the conditions of ionizing radiation have increased. Such materials are nitride coatings based on titanium and chromium. In the work, using X-ray diffraction, X-ray microanalysis, nanoindentation method of Oliver and Farr, scratch testing, the structural phase state and the mechanical properties of nanostructured Cr–N and Ti–Cr–N coatings formed by vacuum-arc deposition from filtered plasma on substrates of steel 12X18H10T and alloy Zr2.5%Nb are investigated. It is established that the coating based on titanium and chromium has a single-phase structure (Ti,Cr)N with a face-centered cubic crystal lattice (FCC), and the coating based on chromium consists of chromium nitride CrN (FCC). It is shown that the Ti–Cr–N coating has greater hardness and toughness than the Cr–N coating. The Ti–Cr–N coating, due to its alloying with Ti atoms, has a higher adhesive strength as compared to the Cr–N coating. At the same time, in the Ti–Cr–N coating, the adhesive strength for a substrate made of Zr2.5%Nb alloy is ≈2 times greater than for a substrate based on steel 12X18H10, which may be associated with the formation of solid solutions between Ti and Zr elements. It is shown that on the contrary, the Cr–N coating can withstand heavy loads before tearing from a substrate based on steel 12X18H10T than from that based on a Zr2.5%Nb alloy. On the basis of the obtained data, one can say about the positive effect on the mechanical properties of titanium additive in the chromium-based coating composition.Исследовано структурно-фазовое состояние, изучены механические свойства методом наноиндентирования по методике Оливера и Фарра и определена нагрузка, при которой происходит отслаивание покрытий Cr–N и Ti–Cr–N, сформированных методом вакуумно-дугового осаждения на подложках из стали 12Х18Н10т и сплава Zr2,5%Nb. Установлено, что покрытие Ti–Cr–N имеет однофазную структуру (Ti,Cr)N с гранецентрированной кубической кристаллической решеткой (ГЦК), а покрытие Cr–N состоит из нитрида хрома CrN (ГЦК). Показано, что покрытие Ti–Cr–N обладает большей твердостью и вязкостью, чем покрытие Cr–N. Вследствие легированности атомами Ti, покрытие Ti–Cr–N имеет более высокую нагрузку отслаивания по сравнению с покрытием Cr–N. При этом у покрытия Ti–Cr–N нагрузка отслаивания от подложки из сплава Zr2,5%Nb в ≈2 раза большая, чем от подложки из стали 12Х18Н10т, в то время как покрытие Cr–N, напротив, выдерживает большие нагрузки до отслаивания от подложки из стали 12Х18Н10т, чем от сплава Zr2,5%Nb

Nanostructured composite materials on the base of titanium and zirconium… 45 SCIENTIFIC PROBLEMS OF MACHINES OPERATION AND MAINTENANCE 1 (161) 2010 Nanostructured composite materials on the base of titanium and zirconium with modified surface layers for m

K e y w o r d s Titanium, zirconium, modified surface layers. S u m m a r y This paper presents the results of the investigations of mechanical and tribological properties of ultrafine-grained and nanostructured titanium and zirconium under microplasma and ion beam treatments. It indicates that the nitrogen ion beam treatment of titanium and zirconium at low temperatures essentially increases the wear resistance by 35-50 times and reduces the friction coefficient by 40%. The biocomposite (nanostructured titanium -calcium phosphate coating) demonstrates a high friction coefficient (0.4-1.0) in tribological interaction with an ultrahigh molecular polyethylene imitated of subcutaneous tissue and bone tissue that allows to eliminate the microdisplacements of an implant against bone tissue under friction and to increase its fixation. A considerable improvement of tribological characteristics of the nanostructured titanium and zirconium with the modified surface layers give the advantages for these materials in medicine and engineering

STRUCTURAL PHASE STATE AND TRIBOTECHNICAL PROPERTIES OF CASTINGS FROM HIGH-CHROME STEEL 20Cr15Mn3, OBTAINED BY TECHNOLOGY OF PRECISION SOL-GEL CASTING IN CERAMIC FORMS

The structure, phase composition and tribotechnical properties of the impeller casting for oil and centrifugal pumps made from high-chromium steel 20Cr15Mn3, obtained by the technology of precise casting, were studied. It was concluded that impeller casting made from high-chromium steel 20Cr15Mn3, obtained by the technology of exact casting of Sol-Gel in ceramic molds, had improved properties and can serve as a replacement for the traditionally used material – cast iron

The influence of heat treatment on the structural phase state and durometric properties of small-sized castings from a copper alloy Cu-Cr-Al

The effect of heat treatment on the structural-phase state and hardness of small-sized castings made from the Cu-Cr-Al copper alloy obtained by casting in a water-cooled metal mold is studied. Using X-ray diffraction analysis, it was found that the castings consist of a matrix solid solution based on copper. The increased value of the crystal lattice parameter of the copper phase is associated with aluminum atoms dissolved in it. After a low-temperature (450 °C) tempering for 10 hours, the crystal lattice parameter of the matrix solid solution decreases, which is associated with the formation of the Al8Cr5 intermetallic compound on the surface of the casting.It is established that after heat treatment (hardening and tempering), the hardness of castings from the Cu-Cr-Al alloy increases by 1.5 times

Structure, physical and mechanical properties of bronze castings obtained by continuous and centrifugal casting

The influence of crystallization conditions (continuous and centrifugal casting) of small-sized BrА1Fe4Ni4 bronze castings on the structure, phase composition, and hardness was studied. It was found by metallographic and X-ray diffraction methods that the castings consist of (α + γ')-eutectoid, α phase and AlCu, Al2Cu3 intermetallic compounds. The matrix phase in the alloy, crystallized by centrifugal casting, due to its higher alloying with Al atoms, has an increased value of the crystal lattice parameter, compared with the case of continuous casting. The hardness of the casting obtained by centrifugal casting increases compared with continuous casting, which is due to the formation of a more dispersed structure, as well as a large solid solution hardening of the matrix phase of the casting

RESEARCH OF THE TRIBOLOGICAL PROPERTIES OF CAST SILUMIN АК15М3

A comparative study of the tribological properties of antifriction silumin casting АК15М3 and typical bronzes БрОЦС, БрОФ and БрАЖ at the friction in the lubricant-20A in a wide range of sliding velocities and pressures of the tests. The conclusion is made that the silumin АК15М3 can be used to replace anti-friction bronze type БрОЦС, БрОФ and БрАЖ in highly loaded friction units