Oxidation of alloy Ti6242S in the temperature range of 500 – 800°C in an air atmosphere is investigated by x-ray diffraction analysis, nuclear microanalysis, optical and electron microscopy. The effect of the content of oxygen at the oxide/metal interface on the lattice constants of the phases is assessed using XRD. It is shown that the concentration of oxygen in the gas-saturated layer depends on the temperature and the time of the annealing. The results obtained are expected to raise the reliability of prediction of the oxidation behavior of the alloy.

The results of a study of the resistance to fatigue fracture of the sheets made of the heat-resistant titanium alloys VT18U (Ti–6.5Al–4.3Zr–2.4Sn–0.8Nb–0.7Mo–0.1Si, wt

Исследовано окисление сплава Ti6242S в диапазоне температур 500 – 800 °C в воздушной атмосфере методами рентгеноструктурного анализа, ядерного микроанализа, световой и электронной микроскопии. Проведена оценка влияния содержания кислорода на границе раздела оксид/металл на периоды кристаллической решетки фаз с использованием метода рентгеноструктурного анализа. Обнаружено, что концентрация кислорода в газонасыщенном слое зависит от температуры и времени отжига. Использование полученных результатов позволяет повысить надежность прогнозирования поведения сплава при окислении.

In this paper the decomposition and evolution of microstructures of the metastable β-phase during aging of Ti10V2Fe3Al, VST5553, and Beta-21S alloys were studied. A comparative study of the evolution of the microstructure and crystal lattice of phases in alloys during aging has been carried out. Features of the nucleation and growth of the secondary α-phase formed during aging were observed using scanning electron microscopy. The concomitant diffusion redistribution of alloying elements between the phases was studied using the method of full-profile X-ray diffraction analysis. It has been established that during aging, the change in the periods of crystal lattices in the studied alloys has a general pattern, which is associated with the common nature of the process of diffusion redistribution of alloying elements between phases. The morphology formed during the decomposition of the secondary α-phase differs between alloys and is determined by the stability of the β-phase after quenching.

The mechanical properties and structure of Ti–6Al–2Sn–4Zr–2Mo–0.1Si (Ti6242S) and Ti–6Al–7Nb alloys subjected to annealing in air at 700°C for 100 h are studied. The Ti–6Al–7Nb alloy in the oxidized state is shown to retain plasticity; this fact was not observed for the other alloyed titanium compositions. The cause for such mechanical behavior of the Ti–6Al–7Nb alloy is related to the substantially lower gas saturation of its surface during annealing.

The effect produced by the rate of heating to the aging temperature of 500°C on the character of phase transitions, the formation of a phase-structure state, and the change in hardness in the quenched Ti–10V–2Fe–3Al titanium alloy with different carbon contents has been studied by differential scanning calorimetry (DSC), scanning electron microscopy, X-ray diffraction analysis, and durometry. It has been shown that the change in the heating rate and carbon content of the alloy has an effect on the temperatures of the exothermic peaks of phase transitions associated with that the metastable solid β-solution formed under quenching decomposes in the process of heating. It has been established that a decrease in the rate of heating to the aging temperature from 40 to 10°C/min and an increase in the carbon content from 0.008 to 0.034 wt % in the quenched Ti–10V–2Fe–3Al alloy improves the dispersity of secondary phases formed after quenching and thereby promotes a growth in the alloy hardness. The effect of the heating rate and carbon content on the change in the parameters calculated by the full-profile analysis of X-ray diffraction pattern for the phases detected after treatment is considered.

Isothermal oxidation testing of near α titanium alloys VT18U, VT20, Ti6Al7Nb and Ti6242S was performed in air at 560 °С for 1000 hours. Parameters of diffusion layer on the alloy surfaces were studied by microhardness indentations, optical microscopy, X-ray diffraction analysis and nuclear microanalysis. It was established that concentration of oxygen in diffusion layer of tested alloys after oxidation differs significantly. An approach was demonstrated and validated by nuclear microanalysis data that allows comparative evaluation of the total concentration of interstitial impurities in the diffusion layer by the X-ray diffraction method.

Рассматриваются причины необычного деформационного поведения тугоплавкого ГПУ-металла рения при комнатной температуре, когда при приложении растягивающих нагрузок он демонстрирует низкую пластичность, а при их отсутствии ведет себя как пластичный металл. The cause for the peculiarity of polycrystalline rhenium at room temperature, which exhibits low plasticity under tension, while behaves like a ductile metal when tensile stress is absent, is considered.

The VST3331 titanium alloy in three structural states with different dispersities of the secondary α phase of titanium has been investigated by scanning electron microscopy and X-ray diffraction analysis. The possibility of using full-profile analysis of X-ray diffraction patterns for determining the size of titanium secondary α-phase crystallites has been estimated. It is demonstrated that the methods in use yield similar estimates of the average thickness of titanium secondary α-phase plates.

The influence of the isothermal annealing conditions in air (at 560 and 625°C for 1000 h) on the deformation behavior of a high-temperature VT18U titanium alloy under tension is studied. The plasticity of the alloy at room temperature decreases from 14 to ≈5% after annealing at the investigated temperatures. The thickness of the gas-saturated layer is 17 and 42 μm after annealing at 560 and 625°C, respectively. The main factor determining the plasticity of the alloy in the oxidized state is the oxygen content gradient in the gas-saturated layer.

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We study the effect of the content of oxygen (carbon) impurities on the temperature of complete polymorphic α + β→β transformation (Tpt) and a set of properties of Ti – 10% V – 2% Fe – 3% Al and VST5553 (Ti – 5% Al – 5% V – 5% Mo – 3% Cr) titanium alloys in the thermally hardened state. We determine the microstructure of the alloys by metallographic analysis and test them for tension and fracture toughness. The dependence of Tpt on the content of impurities in the analyzed alloys is determined. It is shown that the value of Tpt can be found by the method of differential scanning calorimetry whose accuracy is comparable with the accuracy of the method of test quenching. The dependences of the strength and ductile properties of the alloys in tension on the aging temperature are constructed. We also establish the relationship between the fracture toughness of the alloys and the morphology of the primary α-phase.