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

• Published in: Calphad Vol. 35; no. 3; pp. 403 - 410
• Main Authors: Wu, Changjun, Su, Xuping, Liu, Daniel, Wang, Xinming, Wang, Jianhua, Li, Zhi, Peng, Haoping
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.09.2011; Elsevier
• Subjects: Alloys; Assessments; CALPHAD; Computer simulation; Cooling rate; Cross-disciplinary physics: materials science; rheology; Differential thermal analysis; Exact sciences and technology; Intermetallics; Materials science; Mathematical models; Metastable compound; Phase diagram; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Phase diagrams of metals and alloys; Physics; Thermodynamics; V–Zn system; X-rays; Metastable compound; Intermetallics; V–Zn system; CALPHAD; Phase diagram; Phase diagrams; Intermetallic compounds; Vanadium; Binary systems; Differential thermal analysis; XRD; Zinc; Thermodynamic model; V-Zn system; Transition elements; Phase equilibria
• ISSN: 0364-5916; 1873-2984
• DOI: 10.1016/j.calphad.2011.05.005

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 Zn 16, with a V content of about 5.8 at.%, was indeed an equilibrium phase. DTA results indicated that the peritectic temperature for V Zn 16 was about 427  ∘C. Two new metastable compounds, V Zn 9 and V 3Zn 2, 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 Zn 9 was formed at around 450  ∘C in Zn75V25 alloy with a cooling rate greater than 12  ∘C/min. The V Zn 9 phase, however, decomposed into V Zn 3 and liquid Zn when the alloy was held above 442  ∘C. The peritectic temperatures for two equilibrium phases, V 4Zn 5 and V Zn 3, 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 Zn 3 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 Zn 3 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. ► V Zn 16 was confirmed to be an equilibrium phase. ► Two metastable compounds, V Zn 9 and V 3Zn 2, were discovered. ► The solubility of Zn in α -V was measured. ► The V–Zn system was reassessed thermodynamically.