Highly dispersed powders of two-phase multicomponent alloys have been prepared by mechanochemical synthesis from Hf0.5Nb0.5Ta0.5Ti1.5Zr1 (composition 1) and HfNbTaTiZrMo (composition 2) refractory-metal mixtures in a Fritsch (P-7) planetary mill under an Ar atmosphere. Two solid solutions, with BCC and HCP lattices, were obtained from the five-component mixture (composition 1). In the case of the six-component mixture (composition 2), both solid solutions had BCC lattices. Using compaction by hot isostatic pressing at a temperature of 1200°C, we obtained dense samples. Mechanical tests in compression showed a combination of high strength and plasticity. For sample 1, we obtained a yield stress σy = 1317 MPa, compressive breaking stress σb = 1340 MPa, and relative breaking spread of 7%. Even better results were obtained for sample 2: σy = 2153 MPa and σb = 2165 MPa, with δ = 10%.

Multicomponent (Cr, Fe, Co, Ni, Al, Ti, and Nb) powder alloys prepared by milling five- to seven-component equiatomic mixtures of elemental powders in a Fritsch (P-7) planetary mill have been characterized by differential thermal analysis and X-ray diffraction. The results demonstrate that, if the starting mixture contains Al, the BCC solid solution formed as a result of the milling undergoes heating-induced CsCl-type ordering (β-phase). If not only Al but also Ti are present in the starting mixture, further heating causes the β-phase to convert to an L21 phase with the composition (Ni,Co)TiAl. The elements Cr and Fe form a tetragonal σ-phase. The presence of Nb in the starting mixture suppresses the formation of the σ- phase and favors the formation of a hexagonal Laves phase of complex composition: (Fe,Co)CrNb.

Quasicrystalline Al–Cu–Fe–Cr alloys have been prepared by mechanical activation. The morphology of powder particles has been investigated after thermomechanical processing under various conditions. We have identified the sequence of phase transformations in the quaternary alloys in the stability region of quasicrystalline phases and optimized conditions for obtaining a maximum fraction of a decagonal state in powder materials.

This paper presents a detailed study of the formation of chromium-based alloys, Cr–Ta–W + plasticizing additives (Nb and Zr) and Cr–Ta–Si, during milling of powder mixtures in a Fritsch (P-7) planetary mill under an Ar atmosphere. It is shown that, after milling for 18 h, all the components of the starting mixtures convert into a Cr-based BCC solid solution. The powders of chromium alloys obtained in this study are readily compacted by hot isostatic pressing (HIP) under conditions typical of the processing of powders of high-temperature nickel alloys. Heating of the powders and compacts leads to the decomposition of the supersaturated solid solution and the formation of two forms of the Cr2M Laves phase with cubic crystal lattices. The formation of a mixed-phase fine microstructure in the chromium alloys after HIP suggests that the materials studied here are potentially attractive as a base of next-generation chromium-based high-temperature alloys.

Using mechanochemical synthesis through milling of equiatomic multicomponent mixtures of Cr, Fe, Co, Ni, Al, Ti, Mo, and Nb metals in various combinations, we have synthesized powder alloys with different phase compositions: amorphous phase (AP), AP + BCC phase, AP + BCC phase + MO, and FCC + BCC phases. The FCC phase has been shown to be a Ni-based solid solution. The presence of aluminum in a starting mixture helps to stabilize the BCC phase owing to the formation of a disordered B2 phase. Al dissolves in both the BCC and FCC solid solutions, increasing their lattice parameters. In Al-free starting mixtures, Cr is responsible for the formation of the BCC solid solution. The formation of an AP during milling of multicomponent mixtures is favored by the presence of transition metals with a large atomic radius: Ti, Mo, and Nb.

Методом механохимического синтеза (МС) получены трех- и четырехкомпонентные сплавы систем Nb–Al–Si и Nb–Al–Si–С. Показано, что при помоле трехкомпонентной смеси 62Nb + 19Al + 19Si, состав которой отвечает составу интерметаллида Nb10Al3Si3, образуется аморфная фаза (АФ), а из смеси 86Nb + 9Al + 5Si, соответствующей твердому раствору, формируется двухфазная смесь – АФ и наноструктурный (7 нм) ОЦК-твердый раствор. Добавка графита в исходные смеси не только гомогенизирует, но и диспергирует продукты МС до 2 нм. При помоле смеси состава Nb10Al3Si3С10 фазовый состав не изменяется. При помоле смеси 78Nb + 8Al + 5Si + 9С появляется дополнительная фаза – нанодисперсный карбид ниобия. На основе ДТА установлена последовательность перехода МС-сплавов к равновесному состоянию. После компактирования МС-порошков методом горячего изостатического прессования образцы, содержащие графит в исходных смесях, были более однородными как для сплавов на основе интерметаллида, так и для твердых растворов на основе Nb. Нанокарбиды, выделяющиеся по границам зерен, почти на 30% увеличивают твердость сплавов HV: от 12.75 до 18.13 ГПа для образцов, соответствующих интерметаллиду, и от 4.76 до 6.85 ГПа для образцов, соответствующих твердым растворам.

Ternary and quaternary alloys of the Nb-Al-Si and Nb-Al-Si-C systems have been produced by mechanochemical synthesis. Our results demonstrate that the milling of a 62Nb + 19Al + 19Si ternary mixture, whose composition corresponds to that of the intermetallic phase Nb10Al3Si3, leads to the formation of an amorphous phase, whereas the milling of a 86Nb + 9Al + 5Si mixture, corresponding to a solid solution, results in the formation of a two-phase mixture, consisting of an amorphous phase and a nanostructured (7 nm) bcc solid solution. The addition of graphite to the starting mixtures homogenizes the MS products and reduces their particle size to ≃2 nm. The milling of a mixture with the composition Nb10Al3Si3C10 causes no changes in phase composition. The milling of a 78Nb + 8Al + 5Si + 9C mixture leads to the formation of an additional phase: nanoparticulate niobium carbide. Using differential thermal analysis, we have identified the sequence of transformations underlying the transition of the MS alloys to an equilibrium state. After the compaction of the MS powders by hot isostatic pressing, the samples prepared from the graphite-containing mixtures were more homogeneous in the case of both the alloys based on the intermetallic phase and the Nb-based solid solutions. The carbide nanoparticles precipitating on grain boundaries increase the hardness H V of the alloys by almost 30%: from 12.75 to 18.13 GPa for the samples corresponding to the intermetallic phase and from 4.76 to 6.85 GPa for the samples corresponding to solid solutions.

Solid solutions Ni(Al, Mo, C) are formed via milling the Ni2.8Al1Mo0.2 and Ni3Al0.8Mo0.2 and graphite-containing Ni2.8Al1Mo0.2C(0.25, 0.5) and Ni3Al0.8Mo0.2C(0.25, 0.5) mixtures. In this case, some amount of Mo remains beyond the solid solution. Graphite added to a starting mixture decreases the Mo solubility and favors the amorphization of solid solutions. The complete amorphization was found for the mixture with the 5 at % C and 5 at % Mo, which was added instead of Ni. The heating of mechanically synthesized(MS) powder alloys leads to the ordering of carbon-free and carbon-containing solid solutions with the formation of the L1(2) and E2(1) structure, respectively. In the course of the ordering of the Ni(Al, Mo, C) solid solutions, Mo and carbon precipitate in the form of the molybdenum carbide(Mo2C) second phase. The hardness of the MS three-phase Ni-Al-Mo-C solid solutions subjected to hot isostatic pressing is determined by the mass fraction of the formed Mo2C carbide. It is shown that the carbon content in the multicomponent anti-perovskite can be estimated by analyzing the ratio of integral intensities of superlattice reflections I-(100)/I-(110).

A quasicrystalline compound of composition Al64Cu24Fe12 has been prepared through mechanical activation. We have studied the morphology of powder particles after heat treatment under various conditions, identified the sequence of phase transformations in Al-Cu-Fe alloys in the stability region of the ico-phase, and optimized conditions for the preparation of powders containing the maximum possible percentage of the quasicrystalline phase.

Помолом смесей составов Ni2.8Al1Mo0.2 и Ni3Al0.8Mo0.2, а также с добавкой графита Ni2.8Al1Mo0.2C(0.25, 0.5) и Ni3Al0.8Mo0.2C(0.25, 0.5) сформированы твердые растворы Ni(Al, Mo, C), при этом часть Mo не входит в твердый раствор. Введение графита в исходную смесь уменьшает растворимость Mo и способствует аморфизации твердых растворов. Для смеси с добавкой 0.5 ат. % С, в которой 5 ат. % Mo было добавлено вместо никеля, отмечена полная аморфизация. Нагрев механосинтезированных (МС) порошковых сплавов приводит к упорядочению твердых растворов по типу L12 (без углерода) или Е21 (при внедрении углерода). При упорядочении твердых растворов Ni(Al, Mo, C) происходит выделение Mo и углерода с образованием в качестве второй фазы карбида молибдена (Mo2C). Твердость МС трехфазных сплавов системы Ni–Al–Mo–C после горячего изостатического прессования определяется массовой долей образовавшегося карбида Mo2C. Показана возможность оценить количество углерода в многокомпонентном антиперовските на основании анализа соотношения интегральных интенсивностей сверхструктурных линий I(100)/I(110).

The energetics and structural properties of native, substitutional and interstitial defects in Ni3Al have been investigated by first-principles methods. In particular, we have determined the formation energies of composition conserving defects and established that the so-called penta defect, which consists of four vacancies on Ni sublattice and Ni antisite on the Al sublattice, is the main source of vacancies in Ni3Al. We show that this is due to the strong Ni-site preference of vacancies in Ni3Al. We have also calculated the site substitution behaviour of Cu, Pd, Pt, Si, Ti, Cr, V, Nb, Ta and Mo and their effect on the concentration expansion coefficient. We show the latter information can used for an indirect estimate of the site substitution behaviour of the alloying elements. The solution energy of carbon and its effect on the lattice constant of Ni3Al have been obtained in the dilute limit in the first-principles calculations. We have also determined the chemical and strain-induced carbon-carbon interactions in the interstitial positions of Ni3Al. These interactions have been subsequently used in the statistical thermodynamic simulations of carbon ordering in Ni3Al.

An amorphous-crystalline two-phase (amorphous phase + BCC solid solution) powder alloy has been produced by mechanochemical synthesis (MS): by grinding an equiatomic mixture of Cr, Fe, Co, Ni, Al, and Ti metals in a Fritsch (P-7) ball mill at a powder-to-ball weight ratio of 1: 8. Using X-ray diffraction, X-ray microanalysis, and scanning electron microscopy, we have determined the sequence of reaction steps during milling of the mixture. In the early stages of milling (2 h), we observed the formation of an ordered phase (B2), Al + Ni → NiAl, and the CoHCP → CoFCC polymorphic transformation. Milling for 3 h led to the formation of a BCC solid solution. Further milling produced an amorphous phase (AP). In the range 6–25 h of milling, the percentage of the AP increased and that of the BCC solid solution decreased. The phase transformations induced by heating the alloy to 1200°C after MS have identified using differential thermal analysis and X-ray diffraction: \(MS (FCC + AP)\xrightarrow{{450^ \circ C}}(B2)\xrightarrow{{650^ \circ C}}(L2_1 + BCC)\xrightarrow{{850^ \circ C}}L2_1 + \sigma - phase\) (FeCr structure). Prolonged milling has been shown to stabilize the metastable BCC solid solution at temperatures of ≃650°C.

Механохимическим синтезом (МС) смеси металлов Cr, Fe, Co, Ni, Al, Ti эквиатомного состава в шаровой мельнице FRITSCH (P-7) при соотношении массы порошка к массе шаров 1 : 8 получен порошковый аморфно-кристаллический двухфазный сплав (АФ+ОЦК-твердый раствор). Методами рентгенофазового, локального рентгеноспектрального анализа, сканирующей электронной микроскопии определена стадийность взаимодействия компонентов при помоле смеси: на ранних стадиях помола (2 ч) отмечено появление упорядоченной фазы (В2): Al+Ni NiAl и полиморфное превращение CoГПУ CoГЦК; после 3 ч помола появляется ОЦК-твердый раствор; продолжение помола приводит к формированию аморфной фазы (АФ). В интервале 6–25 ч помола происходит увеличение количества АФ за счет уменьшения количества ОЦК-твердого раствора. Методами ДТА и РФА идентифицированы фазовые превращения при нагреве МС-сплава до 1200°С: МС (ОЦК+АФ) L21+ОЦК) L21+ -фаза (тип FeCr); показано, что длительный помол стабилизирует метастабильный ОЦК-твердый раствор при температурах 650°.