Abstract is not available

The solute strengthening due to oxygen in Zircaloy-2 was investigated over the temperature range 1023 to 1873 K. The flow stress was determined in constant true strain rate hot compression over the strain rate 10('-4)-10('-1)s('-1). In order to provide data for LOCA modelling, the 0 concentration range 1260 to 12360 ppm was investigated. For the single phase (alpha) and (beta) materials, the flow curves were normal, whereas the ((alpha)+(beta)) materials exhibited significant yield drops and strain aging, especially when over 50 vol.% (beta) was present. These effects are attributed to the enrichment of the (beta) phase by the solutes Fe and Cr, which are considered to form ordered zones of the Zr(Fe,Cr)(,2) type in the vicinity of dislocations. The flow stress for both the (alpha) and (beta) Zircaloy-2 obeyed the relationship (sigma) = (sigma)(,0) exp(kc), where (sigma)(,0) and k are constants and c is the wt.% 0. The experimental values indicated that 0 strengthens the (beta) phase less effectively than the (alpha) phase. Rule of mixtures calculations were carried out to predict the flow stresses of the ((alpha)+(beta)) alloys; these agreed reasonably well with the experimental data, as long as due allowance was made for the 0 enrichment and 0 empoverishment of the (alpha) and (beta) phases, respectively. / Within the experimental range, the rate sensitivities increased with temperature from 0.13 to 0.20 and from 0.27 to 0.32 for the fully (alpha) and fully (beta) materials. By contrast, the m vs. T curves for the two-phase materials were marked by a rapid increase in m near the beginning and end of the ((alpha)+(beta)) domain, with a dip at large (beta) fractions, particularly in the high 0 alloys. The dip in rate sensitivity was associated with significant strain aging. The experimental activation energies decreased with stress from 440 to 330 kJ/mol (50 to 140 MPa) and from 150 to 125 kJ/mol (1 to 5 MPa) for the (alpha) and (beta) Zircaloy-2 respectively. The extrapolated zero-stress values of Q increased with 0 concentration from 520 to 570 kJ/mol and from 170 to 260 kJ/mol for the (alpha) and (beta) materials, respectively. These data indicate that high temperature dynamic recovery is easier to activate in the (beta) phase but is more sensitive to oxygen than is (alpha) Zircaloy-2.

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No description available.