Molybdenum – Niobium – Zirconium

Savitskii and Zakharov [1963Sav] published small sketches of three T-c-sections from pure Nb to Mo67Zr33, Mo48.74Zr51.26 and Mo24.07Zr75.93, as well as an isothermal section at 1800°C. [1964Pop] reported an isothermal section at 1400°C and some solidus isotherms, which must be taken with care as they define a very wavy solidus surface. [1966Chu] investigated the isothermal section at 1200°C. These two papers show no miscibility gap of the $ phase at the corresponding temperatures. No significant solubility of Nb in the ZrMo2 Laves phase is indicated in the diagrams. [1968Gru] gave the boundaries of the homogeneity range of the $ phase against the two-phase field $ + ZrMo2 in the Zr rich part (> 50 mass% Zr) at 1350, 1200, 1000 and 800°C They constructed also a reaction scheme containing two invariant four-phase equilibria, One of the four univariant equilibria belonging to the upper invariant equilibrium is not consistent. The authors assume a three-phase equilibrium between ZrMo2 and two $ phases (Zr rich and Mo+Nb rich) connecting both invariant equilibria. [1968Sve] studied six isothermal sections at 1800, 1600, 1350, 1100, 800 and 600°C. These authors assume the $ miscibility gap to decrease from the binary Nb-Zr system (976°C) and to form a three-phase field ZrMo2 + $' + $'' somewhat below 800°C. The solubility of Nb in the Laves phase ZrMo2 they estimated to be slightly above 20 mass% between 800 and 1350°C, forming a line compound towards ZrNb2. [1975Khe] investigated the vertical section ZrMo2-Nb as part of the section ZrMo2-Nb-Ti of the quaternary system Mo-Nb-Ti-Zr. These authors found the three-phase equilibrium ZrMo2 + $' + $'' up to about 1350°C in this section. [2006Xia] investigated the 1100°C isothermal section by a ternary diffusion couple. They tabulated the compositions of the end points of 28 tie lines of the ZrMo2 + $ two-phase field. For the maximum Nb content of the Laves phase they gave 30.4 at.%, what is significantly higher than reported by [1968Sve] or [1975Khe]. No $' + $'' miscibility gap was found by [2006Xia] at 1100°C. The experimental investigations relevant for phase diagrams are summarized in Table 1. Other publications on ternary Mo-Nb-Zr alloys regard mechanical properties of Mo-Nb-W-Zr alloys [1965Sav], magnetic spin resonance and low temperature specific heat [1967Mas], electric resistivity and Seebeck effect in Nb rich alloys [1980Moo] as well as recrystallization behavior and grain growth of Zr rich alloys [1999Chu1, 1999Chu2, 2001Chu].