Structural Properties and Stability of Metastable Phases in the Zr-Nb System

Abstract:

The lattice parameters of the bcc (b) and omega (W) phases occurring metastably in a series of Zr-rich Zr-Nb alloys have been determined at and above room temperature (TR) using neutron diffraction techniques. In the first place, the effect of temperature changes upon the lattice parameters of the b and W phases in alloys with 10 and 18 at.% Nb was monitored using neutron thermodiffraction. A method of analysis is applied to the data which involves a confrontation between the observed structural properties and an idealised -or ``reference'- behaviour (RB) which admits a simple mathematical description. A generalised form of Vegard's law is adopted as RB for the b phase, whereas a specific RB is proposed for the W structure. The experimental data are well accounted for by this interpretation scheme, leading to a picture of the isothermal reactions occurring at high temperature which involves the transfer of Nb from the W to the b phase. Finally, the neutron diffraction data on the W phase are combined with an electron microscopy study for the alloy with 10 at.% Nb aged at 773 K, which provides information on the composition of this phase and its evolution towards thermodynamic equilibrium.

• Periodical: Materials Science Forum (Volumes 480-481)
• Pages: 565-572
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.480-481.565
• Online since: March 2005
• Authors: G. Aurelio, A. Fernández Guillermet, G.J. Cuello, P.B. Bozzano
• Keywords: Analytical Microscopy, Lattice Parameter, Metastable Phases, Omega Phase, Zirconium Alloys

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