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The Alloy Phase Diagram International Commission (APDIC) promotes the effective dissemination of data on phase diagrams and thermodynamics of phases in accordance with the required quality standards and furthers the application of phase diagrams in research and industry. The annual report of the Ukrainian Commission on Phase Diagrams and Thermodynamics, which is a member of APDIC as one of the national participants, presents information on the findings of Ukrainian scientists in this field in 2017–2019. Information on the research findings is presented in a table, collecting data on the systems studied and results obtained and listing references to the published papers.

The Mo–Ni–B alloys with a boron content ca.41 at % were prepared by arc melting, annealed at subsolidus temperatures and studied by X-Ray diffraction method, differential thermal analysis and SEM/EPMA microscopy, and the incipient melting temperatures were measured by the Pirani-Alterthum technique. Based on the authors’ experimental data and in view of the data published elsewhere, the partial solidus surface projection has been constructed for the first time for the Mo–Ni–B system in the region Mo–MoB1.0–NiB∼0.8–Ni.

Alloys of the ternary Ni–Ti–Zr system containing 50 to 100 at.% Ni that were annealed at subsolidus temperatures were examined by scanning electron microscopy, electron microprobe analysis, and differential thermal analysis. The solidus surface was constructed in this composition range. A new ternary phase of composition Ni69.2Ti12.5Zr18.3 was found.

The melting diagram and reaction scheme (Scheil diagram) of the Al–Ti–Pt system have been constructed for the first time in the composition range 0–50 at.% Pt using the experimental results for as-cast alloys and alloys annealed at subsolidus temperatures. It is established that ternary compounds τ3, τ4, and τ8 form congruently with participation of the liquid phase and compounds τ1, τ2, τ5, τ6, τ7, τ9, and τ11 by peritectic reactions. All compounds take part in phase equilibria with participation of the liquid phase, forming 31 four-phase and 28 three-phase invariant equilibria at temperatures from 1410 to 660°C.

The liquidus surface of the Al–Ti–Pt system has been constructed for the first time on the composition triangle based on studies of the structure and phase composition and measurement of the liquidus temperatures for the as-cast alloys in the composition range 0–50 at.% Pt produced using a series of techniques. The liquidus surface has 23 primary crystallization fields corresponding to τ1–τ9 and τ11 ternary phases and binary phases formed in the boundary systems and to solid solutions based on components. The extension of these fields and the positions of univariant curves and invariant points have been determined. The liquidus surface exists in the temperature range from 1830°C (corresponding to congruent melting of TiPt compound) to 655°C (temperature of the l ⇄ + eutectic in the binary Al–Pt system).

A series of physicochemical analysis techniques are employed to study the phase equilibria in the aluminum corner of the Al–Ti–Pt system at subsolidus temperatures and in the alloy crystallization process. It has been established for the first time that a ternary τ1 phase (AuCu3 structural type) forms by peritectic reaction L + + ⇄ τ1 at 1405°C. On the solidus surface in the studied composition range at 1405, 1310, 1275, 1060, 925, 820, and 660°C, there are seven isothermal planes that participate in invariant four-phase equilibria involving the liquid phase, three of them being peritectic and the others transitional.

Theoretical bases for the calculation of metastable phase transformations with the participation of supercooled multicomponent melts in the framework of the CALPHAD method are considered. A database with parameters for models of thermodynamic properties of phases in the Cu–Ni–Ti–Zr–Hf system for such calculations is presented. The excess term of the Gibbs energy of liquid alloys is described using the associated solution model, and bcc and fcc solid solutions with a mathematical model with Redlich–Kister polynomials. The diagrams of metastable phase transformations with the participation of supercooled liquid alloys and boundary solid solutions are calculated. The composition ranges for obtaining rapidly quenched and bulk amorphous ternary, quaternary, and quinary alloys of the Cu–Ni–Ti–Zr–Hf system are theoretically assessed.

Optical and scanning electron microscopy, electron microprobe analysis, and X-ray diffraction are employed to examine alloys in the Cu–Ti–Zr ternary system, annealed at 750°C, with copper content from 0 to 50 at.%. A partial isothermal section of the phase diagram is constructed at 750°C in the composition range in question. The existence of a continuous series of solid solutions between CuTi2 and CuZr2 isostructural compounds (γ phase, MoSi2 type) is confirmed. The homogeneity ranges of Cu2TiZr ternary compound (τ1, MgZn2 type) and β-(Ti, Zr), (CuTi) (CuTi type), and CuZr (CsCl type) solid solutions are determined.

Quaternary as-cast Ti 96–x Nb 2 Cr 2 Al x and Ti 93–x Nb 5 Cr 2 Al x alloys, where x = 44, 46, 48, and 50, melted from pure components (~99.9 wt.%) in a laboratory arc furnace, were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM/EDX), and differential thermal analysis (DTA). Bending testing and fracture toughness measurements were performed at room temperature, and compression testing was carried out in a range from room temperature to 750°C. The alloys were found to consist mainly of a superfine lamellar structure formed during decomposition of hightemperature phases. In addition, the alloys with 50 at.% Al contain grains of the γ phase, and all others have precipitates of the cubic β/β 0 phase at boundaries of the high-temperature phases because of double enrichment of the last melt drops with Cr. The tests show that the Ti 96–x Nb 2 Cr 2 Al x alloys with 46 and 48 at.% Al possess the most balanced properties.

In the present paper, the constituent binary B–Mo system is re-modelled in order to reproduce genuine homogeneity ranges of the molybdenum borides. Based on this, available descriptions of the constituent B–Ti and Mo–Ti systems as well as new experimental data reported in the literature for the ternary B–Mo–Ti system are used to model the B–Mo–Ti system in the entire composition and temperature ranges. The elaborated thermodynamic description is further applied to calculate selected phase equilibria as to provide a comparison between calculated and experimental results. The calculations are shown to reproduce the experimental data reasonably well, however for few alloys belonging to the domain of primary (Ti,Mo)B 2 crystallization the computed solidus temperatures are about 200 K higher than incipient melting temperatures measured by pyrometry.

In the present paper, the ternary Al–Cr–Ti and binary constituent Al–Cr systems are thermodynamically re-modelled based on new experimental information reported in the literature within the past few years. Few key experiments were performed with selected ternary alloys in order to complement data on phase equilibria in the composition range of common TiAl-based alloys. Six sample compositions were prepared and analyzed in the as-cast and annealed conditions by means of SEM/EDS, XRD and DTA techniques. The elaborated thermodynamic description was applied to calculate selected phase equilibria as to provide a comparison between calculated and experimental results. The calculations are shown to reproduce the experimental data reasonably well.

The study confirmed the stability of the previously reported ternary C-phase ( $$Pm\bar{3}$$ , a = 0.77353(3) nm for Al73.5Pt10Ru16.5), whose composition was found to range between Al73Pt6Ru21 and Al73.5Pt14.5Ru12. The thermodynamically stable decagonal phase was revealed for the first time at 700-900 °C in a small compositional region around Al78Pt6Ru16. It belongs to the D4 structural type (1.65 nm periodicity in the specific direction). The metastable Al-Pt χ-phase (P31c) is stabilized by the addition of only ~1.5 at.% Ru and extends up to ~12 at.% Ru. The lattice parameters for Al76Pt18.6Ru5.4 are a = 1.2256(4) and c = 2.7331(4) nm.

Based on novel experimental data the thermodynamic description of the ternary Al–C–Ti system was subject to optimization using the CALPHAD approach (Thermo-Calc/PARROT). The reaction scheme, the projections of the liquidus and solidus surfaces, as well as a number of isothermal sections and isopleths were calculated using the proposed thermodynamic description and compared with the experimental results. The calculations were shown to adequately reproduce the experimental data. The main feature of the phase equilibria in the system is the existence of three ternary compounds P (Ti3AlC), H (Ti2AlC) and N (Ti3AlC2) forming peritectically from the liquid phase and TiC1−x carbide at 1907, 1865 and 2013 K, respectively. It is shown that these three compounds are thermodynamically stable in a wide temperature interval.