SYMPOSIA PAPER Published: 30 January 2015
STP154320130039

Displacive and Diffusional Transformations of the Beta Phase in Zirconium Alloys

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Phase transformations of zirconium alloys in the solid state are essentially governed by a few general tendencies. The high temperature β(bcc) phase has the tendency to transform into the orthohexagonal structure, the orthorhombic distortion from the hexagonal symmetry depending on the extent of super-saturation with respect to β-stabilizing alloying elements. The β-phase also exhibits the tendency to transform into the ω-phase. The structures of the α, the β, and the ω phases are related through unique lattice correspondences, the Burgers relation for β/α and that involving the collapse of a set of adjacent {222} planes for β/ω. In fact, the structural relationships between these phases are so strong that the same relationships remain valid for both displacive and diffusional transformations. Another strong tendency which is responsible for several phase reactions in Zr-alloy systems is the clustering tendency in the β-phase. Spinodal decomposition, phase separation, monotectoid decomposition, metastable phase reactions during tempering of some martensites are all consequences of this clustering tendency. Depending on the nature of alloying additions, chemical ordering in the α, the β, and the ω phase can be introduced. The present paper illustrates how the interplay of these general tendencies can generate the wide variety of phase transformations in zirconium alloys and how some fundamental issues connected with phase transformation research are elucidated by studying them.

Author Information

Banerjee, S.
Bhabha Atomic Research Centre, Trombay, Mumbai, Maharashtra, IN
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Developed by Committee: B10
Pages: 1–29
DOI: 10.1520/STP154320130039
ISBN-EB: 978-0-8031-7580-8
ISBN-13: 978-0-8031-7529-7