Tamara Ya. Velikanova

Isothermal sections of the Al–Pd–Co alloy system for 50–100 at.% Al

Abstract The Al–Pd–Co alloy system was studied in the range of 50 to 100 at.% Al. Isothermal sections at 1050, 1000, 940 and 790 °C were determined. The isostructural AlCo and AlPd phases form a continuous range of solid solutions. The Al–Pd e-phase(s) region extends up to ∼16.1 at.% Co, Al 3 Pd 2 up to 7.1 at.% Co, M-Al 13 Co 4 , Al 5 Co 2 , Al 9 Co 2 and the Al–Co Z-phase exhibit moderate extensions into the ternary compositional range of the phase diagram. Six stable ternary compounds designated W, Y 2 , U, V, F and C 2 were revealed and characterized.

Novel ytterbium-zinc-silicides and germanides grown from zinc-flux

Abstract Novel ternary ytterbium-zinc-silicides and germanides have been synthesized using pure zinc metal as a flux-solvent. The new compounds, YbZn 2 Si 2 and YbZn 2 Ge 2 crystallize with the BaAl 4 or ThCr 2 Si 2 -type. Yb(Zn,Si) 2 and Yb(Zn,Si) 2− x crystallize with the ThSi 2 and the GdSi 2− x type, respectively. Crystal properties were characterized using X-ray single crystal analysis via Gandolfi and Weissenberg film techniques, by flat specimen X-ray powder diffractometry and in some cases by automatic four circle X-ray single crystal diffractometry. Depending on the heating and cooling program in the synthesis, various lattice parameter values were obtained suggesting the existence of homogeneity regions. Both the Yb-Zn-silicides and the germanide show a temperature independent Pauli-type paramagnetic behaviour down to liquid He temperature consistent with the XAS-measurements revealing an Yb 2+ ground state.

Formation of Quasicrystals and Related Structures in Systems of Aluminum with Transition Metals. Part 2. Binary Systems Formed by Aluminum with 4d and 5d Metals

Numerous systems for aluminum with transition metals have been found to contain quasiperiodic phases (quasicrystals) having symmetries forbidden by classical crystallography. These phases are metastable in binary systems and have been obtained by rapid cooling from the liquid or gaseous phases. Binary quasicrystals are considered along with revised phase diagrams for the systems Al – 4d-M and Al – 5d-M (M from Mo to Pd and from W to Pt).

Decagonal quasicrystal of a new structural type

Abstract A stable decagonal phase of a new structural type was discovered in Al—Pd—Re. This is the second Al-based alloy system after Al—Pd—Mn where both stable icosahedral and decagonal phases are formed. In contrast to the isostructural icosahedral phases of similar Al and Pd concentrations in both systems, the new decagonal phase exhibits periodicity of ∼2.57 vs. ∼1.25 nm in Al—Pd—Mn and is formed at significantly higher Al concentration than that in Al—Pd—Mn. In the tenfold plane, the structural unit of the Al—Pd—Re decagonal phase assumed from the high-resolution electron images is τ times larger in diameter than that in Al—Pd—Mn.

Titanium-Boride Composites

Alloy properties and phase constitutions for ternary Ti-Al-B and Ti-B-X, quaternary Ti-10 at.% Al-B-X (where X=Si, Ge, Sn, Zr, V, or Nb) and some multi-component alloys were investigated on alloys prepared by arc melting. Ascast and annealed samples were studied by metallography, electron probe microanalysis, XRD, DTA, Vickers hardness at temperatures up to 800°C and compression and bend tests. Phase equilibria in the Ti-rich portions of the systems were studied in the two-phase (Ti)+(TiB) and conjugate three-phase fields. Based on the experimental data obtained, contributions of alloying additions to the mechanical properties are estimated and discussed for eutectic alloys.

Melting Diagram for the Cr ― Nb ― C System in the (Cr) ― (Nb) ― ― (NbC) Region

It is shown from experimental tests on alloys in the Cr ― Nb ― C system in the region of the (Cr) ― (Nb) ― (NbC) subsystem at the melting (crystallization) temperatures that there are two nonvariant four-phase equilibria of congruent type: LE ↔ (Nb) + (Nb2C) + (NbCr2) at 1660°C and LE ↔ (NbC) + (Cr) + (NbCr2) at 1620°C; there is also one nonvariant four-phase equilibrium of incongruent transition type LU + (Nb2C) ↔ (NbC) + (NbCr2) at 1680°C; and two nonvariant three-phase equilibria of congruent type: Le ↔ (NbC) + (NbCr2) at 1696°C and Le ↔ (NbC) + (Cr) at 1640°C. A projection of the liquidus surface has been constructed together with the melting diagram for the system in the stated composition region.

Phase Diagram of the Al ― Rh System

Phase equilibria in the Al ― Rh system over the range 15-50 at.% Rh were investigated by the methods of scanning electron microscopy, x-ray diffraction and electron-probe microanalysis.

Structural parameters of the low-temperature metastable form of the carbide W2C

A sufficiently complete spectrum of superstructure reflections was obtained by the x-ray diffraction analysis of a monocrystal to unequivocally determine, for the first time, the ordered structure of W2C annealed for a long time at a temperature below that of its eutectoidal decomposition. It was shown that W2C of eutectoidal composition in a metastable state has a rhombic ordered structure with the lattice parameters a=4.719 ± ± 0.003 nm × 10=c0, b=6.017 ± 0.003 nm × 10 ≈ 2a0, c=5.181 ± 0.003 nm × 10 ≈ √3a0 (a0, c0 ≡ aHCP, cHCP). The specimens were obtained from tungsten alloys containing 30.5 and 35 at. % C, prepared by are melting followed by annealing at ∼2700°C (1 h) and stepwise cooling to 850°C (the total annealing time at temperatures below 1200°C was 538 h).

New high-temperature heat-resistant alloys on the basis of the Cr–Ti–C system

Abstract The outlook is good for the structure and mechanical properties of eutectic alloy Cr–Ti–C in the temperature range from 200 to 1200°C as high-temperature material has shown. The possibilities of increasing high-temperature strength of Cr–Ti–C alloy by alloying with iron, scandium, lanthanum, molybdenum, and rhenium are discussed.

The Cr ― Ta ― C Melting Diagram in the (Cr) ― (Ta) ― (TaC) Region

It has been found from an experimental study on alloys in the Cr ― Ta ― C system in the region of the (Cr) ― (Ta) ― (TaC) subsystem at melting (crystallization) temperatures that there are two nonvariant four-phase equilibria of congruent type: LE ↔ (Ta) + (Ta2C) + (TaCr2) at 1935°C and LE ↔ (TaC) + (Cr) + (TaCr2) at 1675°C; there is also one four-phase nonvariant equilibrium of incongruent transition type: LU + (Ta2C) ↔ (TaC) + (TaCr2) at 1943°C, and two nonvariant three-phase equilibria of congruent type: Le ↔ (Ta2C) + (TaCr2) at 1960°C and Le ↔ (TaC) + (Cr) at 1695°C. The phase diagram for the subsystem has been constructed in the form of projections of the solidus and liquidus surfaces, and a melting diagram has been constructed.