O. L. Semenova

THERMODYNAMIC SIMULATION OF THE Ni Ru BINARY-SYSTEM PHASE DIAGRAM

Calculations have given a consistent set of interaction constants for all the phases of variable composition in the Ni−Ru binary system, and also a set of stability constants for the ruthenium phases in its stable and virtual modifications. These data have been used to calculated a phase diagram for the Ni−Ru system. It is found that there is satisfactory agreement between the calculated phase diagram and the experimental one when one uses the subregular solution approximation for the solid and liquid phases of variable composition.

Structural Phase Transformations in Zr50Co25Ni25 Alloy

High-temperature X-ray diffraction is applied to study for the first time the structural phase transformations in the Zr50Co25Ni25 alloy at 30–800°C. It is shown that this alloy contains one phase at room temperature, with an orthorhombic crystal structure of CrB type. When temperature increases to 400°C, this phase transforms into a tetragonal phase of AuCu type. A phase with a cubic crystal structure of CsCl type and a monoclinic one of TiNi type show up at 800°C. The TiNitype phase remains up to room temperature when the sample is cooled down.

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.

Reactions in the crystallization of Ti-Ni-SC system alloys in the TiNi - Ni - ScNi region

The Ti-Ni-Sc diagram has been examined for nickel contents of 50–100 at. %. The alloys were prepared by arc melting and were examined by metallography, differential thermal analysis, and microprobe analysis. There are four nonvariant equilibria: two incongruent ones and two congruent ones. The minimum melting point of 980°C occurs in alloys with the base composition + + , which form a eutectic.