Stability of the Nb5Si3 phase in the Nb-Mo-Si system
Phase equilibrium between the α-Nb5Si3 and β-Nb5Si3 phases has been studied in the Nb-Mo-Si ternary system. The high temperature β-Nb5Si3 phase is stabilized by Mo additions to yield a relatively narrow α/β two-phase field in the Nb-Mo-Si ternary system. The enthalpy of the α-β phase transformation has been evaluated from the experimentally determined two-phase field boundaries lines in Nb-xMo-37.5Si (x = 0-10) alloys as 21 (±3) kJ/mol-atom. The β-Nb5Si3 phase exhibits a temperature dependent solubility, which results in the formation of Nbss precipitates both in the α- and β-Nb 5Si3 matrices. The orientation relationship between Nbss and Nb5Si3 has been identified by transmission electron microscopy. Lattice parameter variation of the β-Nb5Si3 phase suggests that the departure of the β-Nb5Si3 phase from stoichiometry toward (Nb + Mo) compositions is derived from the anti-site substitution of Nb and Mo atoms for Si sites.
A. Silicides, various, B. Crystallography, B. Phase transformation, B. Thermodynamic and thermochemical properties, D. Electron microscopy, transmission
Sekido, N., K. Hildal, R. Sakidja, and J. H. Perepezko. "Stability of the Nb5Si3 phase in the Nb–Mo–Si system." Intermetallics 41 (2013): 104-112.