Vol 2017, No 9 (2017)

Co₂V and Co₃V alloys are used as examples to discuss the principles of creating modern phase diagrams to take into account the discovery of an ordering–separation phase transition in alloys. The results of electron-microscopic studies of the Co₂V alloy after heat treatment at various temperatures are presented. A comparison of these results with the conclusions based on the existing Co–V phase diagram demonstrates their disagreement. This disagreement is explained in this work. It is concluded that the ordering–separation phase transition should be taken into account in plotting modern phase diagrams. The Fe–Cr and Ni–Cr phase diagrams are considered with allowance for the ordering–separation phase transition in them. A technique is described to determine the ordering–separation phase transition temperature by transmission electron microscopy. The introduction of the concept of the ordering–separation phase transition is shown to change the principles used by researchers to construct phase diagrams.

When analyzing the ternary Ni–Al–M phase diagrams, where M is a group VI–VIII transition metal, we chose the Ni–Al–Co system, where the γ′ and γ phases are in equilibrium with the β phase, as a base for designing alloys with the following physicochemical properties: a moderate density (≤7.2 g/cm³) and satisfactory heat resistance at temperatures up to 1300°C. The structure formation in heterophase β + γ′ alloys during directional solidification is studied. It is found that, in contrast to cobalt-free β + γ′ alloys (where the γ′-Ni₃Al aluminide forms according to the peritectic reaction L + β ⇄ γ′), the alloys with 8–10 at % Co studied in this work during directional solidification at 1370°C contain the degenerate eutectic L ⇄ β + γ. The transition from the β + γ field to the β + γ′ + γ field occurs in the temperature range 1323–1334°C, and the γ′ phase then forms according to the reaction β + γ ⇄ γ′.

The modern concepts of the causes of hot tearing are considered and the influence of the solid fraction growth rate of an alloy is studied. The hot-tearing susceptibility (HTS) of binary Al–(5–73) wt % Zn alloys is investigated using backbone tests. The HTS is found to be maximal at ~25 wt % Zn. This maximum cannot be explained by a change in the effective solidification range, since this range of the alloys decreases monotonically with increasing zinc content. The calculations of nonequilibrium solidification by the Scheil–Gulliver model and the solid fraction growth rate of the alloys under study demonstrate that the increase in the HTS induced by an increase in the zinc content from 5 to 25 wt % is related to the decrease in the solid fraction growth rate at the final stages of solidification. The decrease in the HTS at >25 wt % Zn is associated with an increase in the fraction of eutectic in the alloys (the solid fraction growth rate during the eutectic reaction tends toward infinity) and with a change in its morphology.

The metallothermic (calcium hydride) synthesis of Ti–Nb alloy powders alloyed with tantalum and zirconium is experimentally studied under various conditions. Chemical, X-ray diffraction, and metallographic analyses of the synthesized products show that initial oxides are completely reduced and a homogeneous β-Ti-based alloy powder forms under the optimum synthesis conditions at a temperature of 1200°C. At a lower synthesis temperature, the end products have a high oxygen content. The experimental results are used to plot the thermokinetic dependences o formation of a bcc solid solution at various times of isothermal holding of Ti–22Nb–6Ta and Ti–22Nb–6Zr (at %) alloys. The physicochemical and technological properties of the Ti–22Nb–6Ta and Ti–22Nb–6Zr alloy powders synthesized by calcium hydride reduction under the optimum conditions are determined.

The atom probe tomography of the nanostructure evolution in ODS¹ Eurofer, ODS 13.5Cr, and ODS 13.5Cr–0.3Ti steels under heavy ion irradiation at 300 and 573 K is performed. The samples were irradiated by 5.6 MeV Fe²⁺ ions and 4.8 MeV Ti²⁺ ions to a fluence of ~10¹⁵ cm^–2. It is shown that the number of nanoclusters increases by a factor of 2–3 after irradiation. The chemical composition of the clusters in the steels changes after irradiation at 300 K, whereas the chemical composition of the clusters in the 13.5Cr–0.3Ti ODS steel remains the same after irradiation at 573 K.

The results of high-temperature tensile and compressive tests are used to analyze the effect of a mechanical deformation scheme and the ratio of the initial sizes of the specimens to be upset on the rheological properties of the VT20 titanium alloy.

A technique is developed to estimate the effect of the deformation parameters on the distribution of the mechanical properties of the products made of aluminum alloys. Regression dependences of the mechanical properties on the deformation intensity, the temperature, and the cooling rate are obtained. A software application to CAE systems is developed to predict the distribution of the mechanical properties of the products made of aluminum alloys over their volume.