Yu. B. Kuz'ma

Phase equilibria in the system Zr-W-C

SummaryThe system Zr-W-C was investigated by the methods of X-ray diffraction and microstructural analyses. Phase equilibria at 1500°C were determined for as-cast and annealed alloys. The carbide ZrC dissolves 34 mo%WC at 500°C; at l,950°C. the solubility ofWC increases to 40 mol.yo. As-cast alloys contain the ω- phase, which has a cubic NaCl-type structure (a = 4.25–4.30 A), and is distributed along the 50 at.% C line at 2–10 at.% Zr. It is shown that the solubility of WC in ZrC may be even greater at temperature approaching the melting point of the alloys.

Phase equilibria in the ternary system zirconium-molybdenum-carbon

SummaryThe system Zr-Mo-C was investigated by means of x-ray diffraction and microstructural analyses. Phase equilibria in the system at 1400 and 600°C were established (Fig. 1). The compound Mo2C dissolves about 4 at.% Zr. The ZrC-base solid solution extends up to 90 mol.% Mo3C2. The hexagonal phase Mo3C2 may be stabilized at 1400°C and below by zirconium.

Isothermal section of the molbdenum-iron-boron system

Summary1.The Mo-Fe-B system has been studied by x-ray structural methods and microstructural analyses, and the isothermal cross section at 1000‡C has been constructed.2.It has been found that the ternary phase (Mo, Fe)3B2 has a crystal structure which is superstructural with respect to the U3Si2 type (for the composition Mo2FeB2 a=5.807±0.004 A, c=3.142±0.003 A).3.For the composition MoFe2B4 the existence has been confirmed of a compound with a structure which is superstructural with respect to the Ta3B4 type, and the lattice constants have been determined (a=3.128±0.005 A, b=12.70±0.01 A, c=2.984±0.005 A).4.Iron has a stabilizing effect on the high-temperature modification of MoB.

Phase equilibria in the system molybdenum-chromium-carbon

SummaryThe methods of x-ray diffraction and microstructural analyses were employed for studying the system Mo-Cr-C, and an isothermal section (1350°C) of the system was plotted. At high carbon contents, the alloys which have not been subjected to heat-treatment contain, theω-phase, which has a cubic face-centered structure of the NaCl type (a = 4.24−4.27 A). The carbide Mo2C dissolves up to 46 at.% Cr, and the carbide Cr23C6 up to 15 at.% Mo. It is shown that the Mo atoms dissolved in the carbide Cr23C6 are distributed in an ordered manner.

PHASE EQUILIBRIA IN THE SYSTEM ZIRCONIUM-CHROMIUM-CARBON

SummaryPhase equilibria in the system Zr-Cr-C at 1300°C were investigated by themethods of x-ray diffraction and microstructural analyses (Fig. 2). Zirconium carbide dissolves up to 6 at.% Cr, while chromium carbides dissolve negligible amounts of zirconium. In accordance with results of a thermodynamic calculation, zirconium carbide is in equilibrium with chromium carbides, chromium, and the compound ZrCr2.

X-ray diffraction study of the system niobium-tungsten-boron

SummaryThe system Nb-W-B was investigated by the x-ray diffraction method. The phase equilibria in this system at 1500° C were established (Fig. 1). The compound W2B dissolves 15 at.% Nb, Nb3B2 dissolves 35 at. % W, and NbB dissolves 40 at. % W. The effect of composition on the lattice parameters of solid solutions based on (Nb, W)3B2 and (Nb, W)B is shown in Figs. 2 and 3.

The rhenium-chromium-carbon system

SummaryThe Re-Cr-C system was investigated by means of x-ray and microstructural analyses. Phase equilibria were established for cast alloys at 1300‡ C (Fig. 1). The compound Cr23C6 dissolves about 20 at. % Re, and the resulting solid solution has an ordered arrangement of atoms.

Ternary systems nio bium-rhenium-carbon and tantalum-rhenium-carbon

SummaryThe systems Nb-Re-C and Ta-Re-C were investigated by the methods of x-ray and metallographic analyses. The phase equilibria in these systems at 1800°C were determined (Figs. 1 and 3). In the ascast high-rhenium alloys, a metastableϑ -phase was detected. Theϑ -phase could not be obtained in the pure form; this phase is in equilibrium with NbC and TaC. Theσ -phase does not exist in the system Ta-Re at 1800°C.

Investigation of physicochemical properties of tungsten — Rhenium thermoelectrodes

SummaryThe authors studied some physicochemical properties of tungsten rhenium thermoelectrodes. It is shown that the instability of the work of a thermocouple with these electrodes and the increase in their brittleness are due to the change in the chemical composition during operation.

X-RAY DIFFRACTION STUDY OF THE SYSTEM TUNGSTEN-RHENIUM-CARBON

ConclusionsThe system W-Re-C was studied by the method of x-ray structural analysis. Phase equilibria were established for as-cast alloys and alloys quenched from 2000, 1500, 1000, and 800°C. Rhenium and α-W2C form continuous series of solid solutions. Forthe composition W3Re2C, there exists a ternary compound with a cubic structure which is related to the β-Mn structure (space group P41 3-O7, a=6.859±0.002 A). At temperatures above 2500°C, there exists the ternary carbide (W, Re)C, which has a cubic face-centered NaCl type structure (space group Fm3m-Oh5, a==4.063± 0.001 A). Preliminary data were obtained on the existence of a rhombic low-temperature W2C modification.