Методами дифференциальной сканирующей калориметрии, растровой электронной микроскопии, микрорентгеноспектрального и рентгеноструктурного фазовых анализов, микроиндентирования изучено влияние термического воздействия на структурно-фазовое состояние и физико-механические свойства сплава на основе орторомбического алюминида титана (О-сплава), полученного селективным лазерным сплавлением. Изменение режима селективного лазерного сплавления, а именно повышение величины относительной плотности энергии при синтезе с 49 до 97 Дж/мм3 приводит к эволюции характера пористости образцов после селективного лазерного сплавления: от пористости, связанной с непроплавом частиц порошка, к газовой пористости, наследуемой от пор в порошке. Фиксируемый в О-сплаве при селективного лазерного сплавления метастабильный β-твердый раствор при нагреве со скоростью 50 К/мин до 900 °С претерпевает распад в двух диапазонах температур 300–600 и 650–800 °С. Повышение температуры термообработки с 750 до 900 °С синтезированного О-сплава способствует уменьшению объемной доли и укрупнению размеров О-пластин, выделяющихся при распаде β-твердого раствора, что приводит к уменьшению эффекта дисперсионного упрочнения (роста твердости) и прироста модуля упругости. Рассмотрено влияние величины относительной плотности энергии при селективном лазерном сплавлении на химический состав синтезируемого О-сплава, стабильность фиксируемого β-твердого раствора к процессам распада и формируемый комплекс физико-механических свойств при термообработке. Using the methods of differential scanning calorimetry, scanning electron microscopy, micro-X-ray spectral and X-ray structural phase analysis, microindentation, the influence of thermal effects on the structural-phase state and physical and mechanical properties of an alloy based on orthorhombic titanium aluminide (O-alloy), obtained by selective laser melting, was studied. A change in the selective laser melting regime, namely an increase in the relative energy density during synthesis from 49 to 97 J/mm3 leads to an evolution of the nature of the porosity of samples after selective laser melting from porosity associated with non-melting of powder particles to gas porosity inherited from pores in the powder. The metastable β-solid solution fixed in the O-alloy during selective laser melting, when heated at a rate of 50 K/min to 900 °C, undergoes decomposition in two temperature ranges 300–550 and 700–800 °C. Increasing the heat treatment temperature from 750 to 900 °C of the synthesized O-alloy promotes reduce the volume fraction and the enlargement of O-plates released during the decomposition of the β-solid solution, which leads to a decrease in the effect of dispersion strengthening (hardness growth) and an increase in the elastic modulus. The influence of the relative energy density value during selective laser melting on the chemical composition of the synthesized O-alloy, the stability of the fixed β-solid solution to decomposition processes, and the complex of physical and mechanical properties formed during heat treatment is considered.

Electrode induction gas atomization (EIGA) is a perspective, cost-effective method for producing spherical intermetallic titanium powders used in additive manufacturing. This study investigates the morphology, microstructure, nanoindentation properties, chemical and phase composition of commercial pre -alloyed EIGA powder of the Ti 2 AlNb-based alloy. The effect of particle size distribution on flowability is studied. Ti-23Al-25Nb powder is characterized by a typical dendritic single beta-phase microstructure with almost homogeneous distribution of alloying elements. The dendriti & scy; body is slightly enriched with Nb and the dendritic boundaries are enriched with Al. The temperature ranges of phase transformations are studied using differential scanning calorimetry at a rate of 50 degrees / min. Several phase transformations including beta -iota omega 0 ; beta -iota O; O -iota beta+alpha 2 ; alpha 2 -iota beta are revealed during heating. The activation of the powder oxidation process at temperatures above 700 degrees C is observed.

The impact of selective laser melting (SLM) process parameters on the porosity, microstructure, phase and chemical composition, texture, and physical-mechanical properties of orthorhombic titanium aluminide Ti2AlNb (O-alloy) powder was studied using a range of methods, including hydrostatic weighing, scanning and transmission electron microscopy, X‑ray diffraction analysis, energy-dispersive X‑ray spectroscopy, microindentation, and compression testing. It was demonstrated that an increase in the volumetric energy density within the range of 28 to 139 J/mm3 led to the following effects: 1) increase in the relative density of the obtained O‑alloy from 97 to 99.9

Abstract—Differential thermal analysis, scanning electron microscopy, X-ray diffraction analysis, and microindentation are used to study changes in the structure, phase composition, microhardness, and contact modulus of elasticity of a heat-resistant alloy based on the Ti2AlNb titanium intermetallic compound, depending on the rate of colling (10–80°/min) from heating temperatures of 950 and 970°С. Using the results obtained, thermokinetic diagrams of high-temperature decomposition of the β(B2) solid solution are constructed.

In situ X-ray diffraction studies of a hardened Ti–26 at

Методами световой микроскопии, рентгеноструктурного фазового анализа, микроиндентирования, термодинамических расчетов в ThermoCalc изучено изменение структуры, фазового состава, химического состава фаз, микротвердости по Виккерсу, контактного модуля упругости в высокопрочном титановом α + β-сплаве мартенситного класса VST2 при закалке от температур нагрева в диапазоне 700 – 1000 °C. Показана хорошая сходимость экспериментальных данных и термодинамических расчетов. Установлена взаимосвязь характера изменения микротвердости и контактного модуля упругости в сплаве VST2, закаленном от 700 – 1000 °C, с эволюцией структуры и фазового состава при закалке.

Методами гидростатического взвешивания, растровой и просвечивающей электронной микроскопии, рентгеноструктурного и микрорентгеноспектрального анализов, микроиндентирования, испытания на сжатие изучено влияние режима селективного лазерного сплавления (СЛС) порошка сплава на основе орторомбического алюминида титана Ti2AlNb (О-сплава) на пористость, структурно-фазовое состояние, химический состав, текстуру и физико-механические свойства получаемых образцов. Показано, что увеличение используемой в работе при синтезе объемной плотности энергии в диапазоне от 28 до 139 Дж/мм3 способствует: 1) повышению относительной плотности получаемого О-сплава с 97 до 99,9%, 2) усилению аксиальной текстуры с выраженным направлением 001 в фиксируемом β/B2-твердом растворе, 3) снижению содержания алюминия, повышению содержания ниобия в сплаве и менее значительному его обогащению кислородом. Обнаружено, что отделение от платформы построения и разрезка О-сплава в продольном сечении приводит к нарушению баланса остаточных напряжений в образцах, синтезированных на нагретой до 200 °С подложки, с образованием в них трещин. Выявлены характерные дефекты структуры сплава (поры, непроплавы, химическая неоднородность) после сплавления порошка. Определен комплекс физико-механических свойств, синтезированных О-сплавов (твердость – 390–430 НV, контактный модуль упругости – 91–98 ГПа, предел текучести при сжатии – 1060–1080 МПа, относительное укорочение при сжатии не менее 30%. Рассмотрена связь получаемого уровня свойств в О-сплаве с формируемым при синтезе структурно-текстурным состоянием. The influence of the of selective laser melting (SLM) process parameters of the alloy based on orthorhombic titanium aluminide Ti2AlNb (O-alloy) on porosity, microstructure, phase and chemical compositions, texture, physical and mechanical properties using the methods of hydrostatic weighing, scanning and transmission electron microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy, microindentation and compression testing were studied. It was demonstrated that the increase in the SLM in the range of volumetric energy density from 28 J/mm3 to 139 J/mm3 contributes to: 1) the increase in the relative density of the resulting O-alloy coupons from 97 to 99.9%, 2) the intensification of the solidification <001>-fiber texture of β/B2-solid solution, 3) decrease in Al, increase in Nb content and lesser enrichment with oxygen in the as-built coupons. The separation the O-alloy from the platform and along the building direction results in the imbalance of residual stresses accompanied by the crack formation in samples fused on a substrate preheated at 200°C. The typical defects (pores, lack of fusion, chemical inhomogeneity) after SLM are discussed. A combination of physical and mechanical properties of the synthesized O-alloys coupons was determined (Vickers microhardness - 390...430 HV, contact modulus of elasticity – 91–98 GPa, compressive yield strength 1060–1080 MPa, relative shortening in compression of at least 30%. The relationship between the resulting level of properties and a microstructure-texture in an O-alloy state formed of as-built SLM samples are considered.

The impact of heat treatment on the structural-phase characteristics, physical and mechanical properties of an alloy based on orthorhombic titanium aluminide (O-alloy) produced by selective laser melting was investigated using differential scanning calorimetry, scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction analysis, and microindentation. Modifying the selective laser melting process parameters, specifically increasing the relative energy density from 49 to 97 J/mm3, results in the evolution of the porosity character of the samples after selective laser fusion. This transition is observed from porosity associated with the lack-of-fusion to the gas porosity inherited from the pores in the powder and gas entrapment during melting. The metastable β‑solid solution that is fixed in the O‑alloy during selective laser melting undergoes decomposition in two temperature ranges, 300–600 °C and 650–800 °C, when heated at a rate of 50 °C per minute up to 900 °C. An increase in the heat treatment temperature from 750 to 900 °C of the as-built O‑alloy results in a reduction in the volume fraction and an expansion in the thickness of the O‑platelets precipitated during the decomposition of the β‑solid solution. This phenomenon leads to a decline in the impact of dispersion hardening (hardness growth) and enhancement in the elastic modulus. This study examines the impact of volumetric energy density during selective laser melting on the chemical composition of the O‑alloy, the stability of as-built alloy to decomposition of β‑solid solution and the formation of a combination of physical and mechanical properties during heat treatment.

In situ X-ray diffraction studies of a hardened Ti-26 at % Nb alloy with an initial single-phase beta structure sublected to tension allows studying the processes occurring upon application of deformation and correlating them to three intervals of strain values. The first range of values (up to 0.7%) is the region of elastic deformation of the bcc lattice of the beta titanium solid solution. In the second interval (0.7-1.4%), the occurrence of the strain-induced beta -> tau transformation is recorded, and, as the strain increases to 1.4%, an increase in the c/a parameter of this lattice is observed. In the third strain range (1.4-2.2%), plastic deformation of the beta and tau phases occurs. The resulting tau phase after the test remains quite stable. It is found that after tensile tests, the Young modulus of the hardened Ti-26Nb alloy decreases from 58 to 52-54 GPa, and the microhardness increases from 200 to 240 HV.

Changes in the structure, phase composition, chemical composition, Vickers microhardness, and contact modulus of elasticity of a high-strength titanium α + β-alloy of the VST2 martensitic class during quenching after heating in the 700 – 1000°Ñ range were studied using the methods of optical microscopy, XRD phase analysis, microindentation, and thermodynamic calculations in ThermoCalc. The experimental data were in good agreement with the results of thermodynamic calculations. Arelationship between changes in the microhardness and contact modulus of elasticity of VST2 alloy, quenched from 700 – 1000°C, and the structure and phase composition of the alloy during quenching was established.

Composites based on Nb3(Fe, Al)3 C η-carbide obtained by mechanical alloying are studied. Microstructural and quantitative phase analyses are performed. The phase composition, the density and the hardness are determined. It is shown that mechanical fusion of the elemental components in liquid hydrocarbon followed by annealing can be used to synthesize an Nb3(Fe, Al)3 C η-carbide phase. Spark plasma sintering is used to obtain a composite based on η-carbide (60 wt.

The article analyses data for chemical composition, manufacturing and processing methods for promising heat-resistant alloys based upon orthorhombic titanium intermetallic Ti2AlNb (O-alloys) developed within Russia and abroad. Phase diagrams typical for alloys based upon Ti–Al–Nb and general data for the phases formed in these alloys are provided. Concepts of aluminum and niobium equivalents used for multicomponent alloys are considered. The effect of alloying elements on a combination of mechanical properties of O-alloys, alloying principles, and compositions of the alloys developed are summarized. Characteristics of phase transformations occurring within alloys during heat treatment, including continuous heating and isothermal treatment, are provided. Typical microstructures of the alloys are presented; processing methods for their production and the influence of structural parameters on a combination of properties are described. Methods for manufacturing and processing routes of O-alloys are presented, which provide a good set of properties at room and elevated temperatures, as well as possible operating temperatures for refractory use.

Исследованы композиты на основе h-карбида Nb3(Fe, Al)3C, полученные с использованием метода механического сплавления. Определен фазовый состав композитов. Проведены микроструктурный и количественный фазовый анализы. Определены плотность и твердость композитов. Проведены испытания на изнашивание. Показано, что механическим сплавлением элементарных компонентов в жидком углеводороде с последующим отжигом возможен синтез фазы h-карбида Nb3(Fe, Al)3C. Методом электроимпульсного плазменного спекания получен композит на основе h-карбида (60 масс. %), остальное — фазы Nb5Al3Cx, Nb3Al, Nb, Nb2C и ~ 5 % (масс.) нанопластинок графита. Композит имеет плотность 5,11 ± 0,05 г/см3 при пористости ~ 20 %, твердость 1,4 ± 0,6 ГПа и практически не изнашивается при испытаниях в условиях сухого трения с шариками из закаленной стали и сплава ВК6.

The evolution of phase composition and hardness in the refractory titanium VT18U alloy (Ti–6.4Al–3.5Zr–2.6Sn–1Nb–0.6Mo–0.2Si) during aging for 1 h within a temperature range of 550–700°C has been studied by optical, scanning, and transmission electron microscopy; full-profile X-ray diffraction analysis; and durometry. An explanation is given to some specific features of changes in the crystal lattice constants (unit cell parameters) (β, α', αII, αI , and α2) calculated by means of full-profile analysis for the phases formed under high-temperature treatment at 915°C and further aging in alloy VT18U. It has been shown that a maximum hardness at 650°C in aged alloy VT18U is correlated with a maximum amount of α2-precipitates, which are formed at this temperature and detected by means of full-profile analysis. For an pilot VT18U-based alloy with an increased content of zirconium (7 wt %) and tin (4 wt %), some morphological features in the precipitation of αII and α2-phases have been established alongside with regularities of transformations due to doping with aluminum, zirconium, and tin in the phases (β, αII, αI, α2) formed during aging at 700°C for 100 h.

The effect of continuous cooling at a rate of 1.1 K/min and combined cooling with an isothermal hold at 860 – 940°C on the structure, phase composition and properties of titanium alloy VTI-4 is studied. It is shown that introduction of an isothermal hold into the cooling mode lowers the hardness and elevates the content of untransformed β-phase in the structure of the alloy. The structure of the alloy is shown to be the most homogeneous without a feature of secondary decomposition yielding fine precipitates and with a maximum content of β-phase after an isothermal hold at 800°C for 1 h.

Исследовано влияние непрерывного охлаждения со скоростью 1,1 °C/мин и комбинированного охлаждения с изотермической выдержкой при 860 - 940 °C на структуру, фазовый состав и свойства титанового сплава ВТИ-4. Показано, что введение в режим охлаждения изотермической выдержки способствует снижению твердости и увеличению количества непревращенной β-фазы в структуре сплава. Установлено, что наиболее однородная структура без признаков вторичного распада с образованием дисперсных выделений и с максимальным количеством β-фазы формируется в результате введения изотермической выдержки при 860 °C в течение 1 ч.

A two-stage wet ball milling procedure followed by SPS at 900 degrees C was applied to fabricate the composite based on Ti2AlC MAX phase with the incorporated nanographite. In addition to the MAX phase (71 vol-%) and nanographite (5 vol-%), the synthesized composite contains TiC (7 vol-%) and TiAl (4 vol-%) and Ti6Al16Fe7 G phase (13 vol-%) which is formed under the interaction of the starting powders with iron going from the material of the milling equipment under milling. The MAX phase and G phase form areas of a layered structure with a layer thickness of about 100-200 nm. The density of the composite is 3.95 g cm-3 which is 95% of the calculated, and microhardness being -8.7 GPa. The proposed method for the synthesis of the composite provides high wear resistance to dry sliding friction against a steel ball and the friction coefficient kfr of -0.35, and wear being practically absent.

The present work develops a novel unified approach to describe the crystal structure of orthorhombic martensite (α′′) in Ti alloys independent of chemical composition. By employing a straightforward yet highly instructive solid sphere model for the basic tetrahedral structural unit the crystal structures involved in the β ↔ α′′/α′ martensitic transformation are categorized into several intermediate configurations. Importantly, a new metric is introduced, δ, which unambiguously characterizes the atomic positions inside the orthorhombic unit cell depending on unit-cell geometry. Furthermore, the exclusive use of relative quantities to describe unit-cell geometry and atom positions renders the approach developed herein independent of alloy content. In this way, shortcomings of commonly suggested structural metrics for α′′ are eliminated. Subsequently, the novel methodology is applied to analyse and compare the crystal structure of α′′ across a broad range of Ti alloys based on experimentally measured unit-cell parameters. From this analysis it emerges that a large fraction of structural configurations along the b.c.c.–Cmcm–h.c.p. transformation path is not observed in quenched alloys. The threshold between the not-observed and the remaining well observed configurations is identified with an ideal Cmcm crystal structure, relative to which the experimentally found α′′ is compressed along its c axis.