V. M. Petyukh

The effect of cobalt and nickel on transformation in TiRh

Abstract The transformations in TiRh and the effect of replacement of rhodium in TiRh by cobalt and nickel have been studied. TiRh undergoes two structural transformations which are of first order, exhibit thermoelastic properties and persist in the TiRhCo and TiRhNi ternary alloys. Stabilization of the high temperature phase of TiRh of B2 type crystal structure down to room temperature can be achieved by substitution of cobalt at about 15 at.% and of nickel at about 20 at%. The TiCoTiRh and TiNiTiRh sections of the corresponding ternary systems are found to be quasi-binary.

Alloy Constitution and Phase Equilibria in the Hf–Ru–Rh System. III. Solidus Surface of the Partial Ru–HfRu–HfRh–Rh System

The data obtained by metallography, X-ray diffraction, and electron microprobe and differential thermal analyses, as well as incipient melting points measured with the Pirani-Althertum method, are used to construct, for the first time, the solidus surface of the Hf–Ru–Rh system at 0–50 at.% Hf on the composition triangle. Ruthenium and rhodium solid solutions, ε and θ phases based on HfRh3 (AuCu3-type structure) and Hf3Rh5 (Ge3Rh5 type), and a continuous series of solid solutions between isostructural (CsCl type) phases based on the HfRu compound and its high-temperature modification (δ phase) take place in phase equilibria. Five single-phase surfaces corresponding to solid solutions based on components and binary phases, seven ruled surfaces bounding the two-phase volumes, and three isothermal planes formed by the mentioned phases in invariant four-phase equilibria with participation of liquid (at 1900, 1810, and 1720°C) are constituents of the solidus surface.

Phase Equilibria in the Melting/Solidification Range of B–Mo–Ti Alloys

As-cast B–Mo–Ti alloys and samples annealed at subsolidus temperatures are experimentally studied by X-ray diffraction and scanning electron microscopy with electron microprobe analysis. Solidus temperatures and temperatures of other phase transformations are measured by differential thermal analysis and pyrometry with the Pirani–Alterthum method. No ternary compounds are found in the examined alloys. Based on the data obtained, the B–Mo–Ti liquidus and solidus surfaces have been constructed for the first time.

Phase equilibria in the ternary system Sc−Cr−C at subsolidus temperatures

Phase equilibria in the ternary system Sc−Cr−C were investigated by metallography, differential thermal analysis, x-ray diffraction, and electron probe microanalysis. A projection of the solidus surface was constructed for the first time. The nature of phase equilibria in the system is defined by the presence of two thermodynamically stable phases based on the compounds Sc2CrC3 (whose existence was confirmed) and ScC1−x. The melting point of the alloys increases with increasing carbon concentration. Compositions in the 〈Cr〉+〈ScC1−x〉+〈Sc〉 range have a minimum melting temperature equal to 1018±2°C, and the maximum melting temperature in the system, 1660±2°C, is found in alloys containing 〈Cr3C2〉+〈Sc2CrC3〉+C.

Constitution of Alloys and Phase Diagram of the Hf–Ru–Rh System. IV. Liquidus Surface and Melting Diagram of the Partial Ru–HfRu–HfRh–Rh System

Using the data obtained in study of the as-cast Hf–Ru–Rh alloys in the range 0–50 at.% Hf and considering the solidus surface constitution, physicochemical analysis techniques are employed to construct for the first time the liquidus surface of the Ru–HfRu–HfRh–Rh partial system onto the composition triangle, the melting diagram, and the reaction scheme reflecting processes during crystallization of the alloys. It is shown that five surfaces of primary crystallization of a continuous series of solid solutions between isostructural (CsCl-type) phases formed by compound HfRu and its high-temperature modification (δ phase), ruthenium and rhodium solid solutions, as well as the ε phase based on compound HfRh3 (AuCu3-type structure) and θ phase based on compound Hf3Rh5 (Hf3Rh5-type structure) are parts of the liquidus surface. Three invariant four-phase processes involving liquid take place at 1900, 1810, and 1720°C.

Alloy Constitution and Phase Equilibria in the Hf–Ru–Rh System. II. Liquidus Surface, Melting Diagram, and Vertical Sections of the Partial Hf–HfRu–HfRh System

According to the constitution of the solidus surface in the Hf–Ru–Rh system over the composition range 50−100 at.% Hf and the data obtained in studying the as-cast alloys by physicochemical analysis techniques, we constructed, for the first time, the liquidus surface of the partial Hf–HfRu–HfRh system on the composition triangle and its melting diagram. The vertical sections at 5 at.% Ru, 10 at.% Rh, and 75 and 80 at.% Hf at the ratio Ru : Rh = 1 : 1 are presented. The processes that occur when the alloys are crystallized are shown in the reaction scheme. The primary crystallization regions for a continuous series of solid solutions between isostructural (CsCl type) phases formed by the HfRu compound and its high-temperature modification (δ phase) as well as β-Hf and γ-Hf2Rh (Ti2Ni type) solid solutions are parts of the liquidus surface. An invariant four-phase equilibrium involving liquid, LU + δ ⇆ γ + , is observed at 1373°C in the system.

Constitution of Rh–Sc–Ti Alloys in the 50% (At.) Rh Section and Adjacent Composition Range

Physicochemical analysis methods (metallography, X-ray diffraction, differential thermal analysis, and resistometry) are used to examine phase equilibria in the Rh–Sc–Ti system in the ScRh–TiRh section and in the adjacent composition range. It is shown that the ScRh–TiRh section is quasibinary. Intermetallic ScRh and TiRh phases with the same crystalline structure form an infinite series of solid solutions with cubic CsCl structure at subsolidus temperature. Replacement of titanium by scandium stabilizes the high-temperature phase at room temperature. The martensitic transformation in TiRh alloys proceeds in two stages as follows: cubic (CsCl) → tetragonal (AuCu) → monoclinic (TiNi).

The Quasibinary ZrCo–ZrNi Phase Diagram

Physicochemical analysis methods (metallography, X-ray diffraction, differential thermal analysis, and electron microprobe analysis) are used to first study the ZrCo–ZrNi alloys in the temperature range that includes their melting and crystallization. The phase diagram of the system is constructed. The phases based on ZrCo (crystal structure of CsCl type, maximum nickel solubility about 46 at.%) and ZrNi (crystal structure of CrB type, cobalt solubility about 2 at.%) coexist in a range from room to subsolidus temperatures. The phase diagram is of peritectic type with peritectic point coordinates 1240 ± 12°C and ~48 at.% Ni.

The Constitution of Co–Zr Phase Diagram

The constitution of Co–Zr alloys in the Zr2Co–Zr region is studied by physicochemical analyses (metallography, X-ray diffraction, differential thermal analysis). It is shown that the Zr3Co phase exists in the system, though the literature data on its existence and formation are contradictory. It forms in solid state at 981°C via peritectoid reaction + ↔ , and its homogeneity range at 900°C is no larger than 1 at.%. The eutectic point L ↔ + is found in the alloy with ~22 at.% Co. The microhardness of the Zr2Co and Zr3Co phases is determined.

Cocrystallization of Max-Phases in the Ti–Al–C System

The structure and phase transformations in the Ti–Al–C system were studied by X-ray diffraction, differential thermal analysis, and scanning electron microscopy, including energy-dispersive X-ray spectroscopy and electron backscatter diffraction on samples obtained by arc melting and annealing at high temperatures. The ternary system has a cocrystallization region for the two MAX-phases, N and H. The Ti41.5Al38.5C20 samples contain three phases at all experimental temperatures (from 650 to 1660°C): Ti3AlC2 (N-phase of Ti3SiC2 type), Ti2AlC (H, Cr2AlC type), and binary intermetallic TiAl3 (ε, its own crystal type). The morphology of the as-cast alloy and annealed samples (at temperatures above and below the solidus temperature, 1660 and 1250°C, respectively) shows that invariant solidification at 1405°C (solidus temperature) precedes the univariant simultaneous solidification of N- and H-phases, i.e. both MAX-phases separating from the melt.