The V-Zn binary system: New experimental results and thermodynamic assessment

Experimental investigation followed by thermodynamic assessment of the V-Zn system was carried out in the present study. A series of V-Zn alloys annealed at various temperatures were examined using scanning electron microscopy coupled with energy dispersive spectroscopy/wavelength dispersive X-ray spectrometer, X-ray diffraction and differential thermal analysis. It was confirmed that V Zn₁₆, with a V content of about 5.8 at.%, was indeed an equilibrium phase. DTA results indicated that the peritectic temperature for V Zn₁₆ was about 427 ^°C. Two new metastable compounds, V Zn₉ and V ₃Zn₂, with V contents of 8.5-11.3 at.% and 60 at.%, respectively, were discovered. DTA results together with SEM-EDS examinations revealed that V Zn₉ was formed at around 450 ^°C in Zn75V25 alloy with a cooling rate greater than 12 ^°C/min. The V Zn₉ phase, however, decomposed into V Zn₃ and liquid Zn when the alloy was held above 442 ^°C. The peritectic temperatures for two equilibrium phases, V ₄Zn₅ and V Zn₃, were 651 ^°C and 621 ^°C, respectively. These measurements were slightly lower than the values determined in prior studies. The onset temperature for forming V Zn₃ decreased significantly with increasing cooling rate while its exothermic peak widened during fast cooling. These phenomena indicated that both the nucleation and growth processes for V Zn₃ were kinetically challenged.In addition, the solubility of Zn in α-V was measured. It was 2.1 at.%, 2.5 at.%, 2.6 at.%, 2.9 at.% and 3.3 at.% at 450 ^°C, 600 ^°C, 670 ^°C, 800 ^°C and 1000 ^°C, respectively. Based on the results obtained in the present study and previous investigations, the V-Zn system was reassessed thermodynamically. The assessment was in good agreement with experimental results.