Abstract
A new model describing the structural and bonding properties of the omega phase in Zr–Nb alloys has recently been presented [G. B. Grad et al.: Z. Metallkd. 87, (1996) 726]. This model, which was aimed at explaining the composition dependence of the bonding distances, predicts that the omega phase in Zr–Nb alloys is ordered, i.e., that some of the crystallographic sites are preferently occupied for Zr atoms. This feature of the omega phase is not contradicted by the most recent studies of the lattice parameters, but it has not yet been tested against direct measurements of the atomic ordering. In this paper we identify, theoretically, the Bragg reflections that appear only if the alloy is ordered, and show that among the three prototypical isoelectronic systems Ti–V, Zr–Nb and Hf–Ta, the former is the most suitable one for an experimental test of the model. The use of neutron scattering and transmission experiments is critically discussed, and the optimum composition for experiments with Ti–V alloys is presented.
It is a privilege for the authors to dedicate this work to Prof. inden on the occasion of his 60th birthday. One of us (AFG) has benefited over the years from stimulating conversations with Prof.Inden about various aspects of the phase stability problem.
This work is part of a research project supported by CONICET (Argentina) under grant PIA 6100/96, by Fundación Antorchas (Argentina) under grant A-13434/1-000081, by Cooperativa de Electricidad Bariloche, and by Fundación Balseiro (Bariloche, Argentina).
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