J. Bradbrook, G. Lorimer, N. Ridley
Feb 1, 1972
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2
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Journal
Journal of Nuclear Materials
Abstract
The precipitation of zirconium hydride in iodide zirconium and zircaloy-2 has been studied using, primarily, thin foil electron microscopy. The precipitate crystal structure and distribution has been found to be a function of heat treatment procedure. At rates of cooling of < 2 °C/min, large precipitates of the equilibrium fcc δ-hydride formed mainly at grain boundaries. As the cooling rate was increased intragranular precipitates became more evident. On cooling at 2–10 °C/min the precipitates were mainly δ-hydride, but at rates greater than 10 °C/min the fct γ-hydride became increasingly predominant. These δ- and γ-precipitates were internally twinned. Specimens rapidly quenched to room temperature contained only untwinned γ-hydrides. The orientation relationships between the hydrides and the matrix were measured. Hydrides formed under stress in zircaloy tubing were observed to have similar structures and morphologies to those reported for unstressed material, although the precipitate distribution differed. A martensitic mechanism is proposed for the formation of twinned hydride and twinned and untwinned γ-hydrides, and its implications for the precipitation behaviour of hydrides in the can of a reactor fuel element are outlined.