High temperature (600–800°C) thermally activated deformation behaviour of α-Zircaloy-4-Oxygen alloys

Abstract

The high temperature thermally activated deformation behaviour of Zircaloy-4-oxygen alloys containing oxygen up to 1 wt.% has been investigated. Décrémentai unloading technique (Dip technique) was employed to determine the internal stress ( τ μ ) and thus the effective stress ( τ ∗). Strain rate change tests were done to determine strain rate sensitivity ( m) and activation volume ( V∗). Activation energy ( ΔG μ ) was calculated from the above data. Oxygen was found to produce an increase in y.s. (0.2%), τ ∗ and ΔG μ 0 and a decrease in m and V∗ while τ μ was not affected significantly. These experimental results support the view that the predominant rate controlling mechanism for deformation in this temperature regime is the thermally activated breaking of attractive junctions for these alloys. Oxygen atoms, pairs or clusters of oxygen atoms, are ruled out as barriers, instead the strengthening is attributed to an increase in the core width of the dislocations due to the presence of oxygen. This in turn results in a more stable attractive junction, which is reflected in the increasing values of ΔG μ 0 with the increase in oxygen. Finally it is suggested that the atypical temperature dependence of τ μ / μ and ΔG μ is a direct consequence of dynamic recovery.