Phase Diagram of the Nb—Ge System

Thermodynamic assessment of the Nb–Ge system

“…The solubility of Ge in Bcc-(Nb) measured by Jorda et al [9] increases from 4 ± 1 to 11.5 ± 1 at.% Ge within the temperature range from 1000 to 1900 • C, which is higher than that of 2-8 at.% Ge determined by Pan et al [7] and that of 3-5% at.% Ge by Muller [8]. The (Nb3Ge) phase is formed by a peritectic reaction L + Bcc-(Nb) ↔ (Nb3Ge), which is measured at 1900 ± 10 • C, 18 ± 1 at.% Ge by Jorda et al [9], at 1970 • C, 18 at.% Ge by Pan et al [7] and at 1910 • C, 18 at.% Ge by Muller [8].…”

“…The eutectic reaction L ↔ (Nb3Ge) + (Nb5Ge3) occurs at 1865 • C, 27 at.% Ge measured by Jorda et al [9], (1930 • C, 26 at.% Ge) by Pan et al [7] and 1900 • C, 21.8 at.% Ge by Muller [8]. The congruent melting point of (Nb5Ge3) measured by Jorda et al [9] is 2180 ± 10 • C which is higher than that of 2150 • C by Pan et al [7] and 2065 • C by Muller [8], and the homogeneity range of (Nb5Ge3) extends from 38 to 44 at.% Ge [9] which is distinctly different from the range (34-36 at.% Ge) given by Pan 0925-8388/$ -see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.12.005 Table 1 The experimental data of the Nb-Ge system.…”

“…The (Nb3Ge) phase is formed by a peritectic reaction L + Bcc-(Nb) ↔ (Nb3Ge), which is measured at 1900 ± 10 • C, 18 ± 1 at.% Ge by Jorda et al [9], at 1970 • C, 18 at.% Ge by Pan et al [7] and at 1910 • C, 18 at.% Ge by Muller [8]. The homogeneity range of the (Nb3Ge) phase was confirmed between 18-23 at.% Ge by Jorda et al [9], 15-18 at.% Ge by Pan et al [7] and 18-19 at.% Ge by Muller [8]. The eutectic reaction L ↔ (Nb3Ge) + (Nb5Ge3) occurs at 1865 • C, 27 at.% Ge measured by Jorda et al [9], (1930 • C, 26 at.% Ge) by Pan et al [7] and 1900 • C, 21.8 at.% Ge by Muller [8].…”

“…The present paper deals with an assessment of the thermodynamic description of the Nb-Ge system with the inclusion of the newly confirmed stable phase Nb 3 Ge 2 by means of the CALPHAD (Calculation of Phase Diagram) technique and provides a set of self-consistent parameters for calculation of phase equilibria and thermochemical properties of the system. The complete investigation of the Nb-Ge phase diagram was originally measured by Pan et al [7], including four intermediate compounds (Nb3Ge), (Nb5Ge3), (Nb3Ge2) and (NbGe2) with homogeneity ranges, two terminal solution phases Bcc-(Nb) and Diamond-(Ge), two eutectic reactions and three peritectic reactions. Muller [8] gave a partial phase diagram of the Nb-Ge system at Nb-rich side in the temperature range from 1600 to 2065 • C. Jorda et al [9] later reinvestigated a majority of the Nb-Ge equilibrium phase diagram by means of X-ray diffraction (XRD), metallography, hardness measurements, microprobe analysis and differential thermal analysis (DTA) up to 2200 • C. For temperatures higher than 1870 • C, the solidus lines were determined by thermal analysis on levitating samples.…”

“…[10]. The eutectic reaction L ↔ Nb5Ge3 + NbGe2 was measured at 1580 ± 10 • C, 59 at.% Ge by Jorda et al [9], at 1590 • C, 60 at.% Ge by Pan et al [7] and at 1590 • C by Feschotte et al [10]. The congruent melting point of (NbGe2) is 1680 • C [9].…”