Uniaxial tensile properties of Zircaloy containing oxygen: summary report

The uniaxial stress-strain behavior of Zircaloy-2 and -4, Zircaloy-oxygen alloys with a uniform oxygen distribution, and composite specimens with a ZrO2/α/β layer structure was investigated over the range of experimental conditions: temperature 25-14000C; strain rate 10-6 - 10-1 s-1; oxygen content 0.11 - 4.4 wt %; grain size 5-50 μm; texture longitudinal, transverse, and diagonal orientations; and microstructural state, which consists of the equiaxed α phase and various transformed β acicular structures. The work-hardening and strain-rate sensitivity parameters were determined from the experimental results, and the tensile properties were correlated with oxygen concentration, oxygen distribution in the material, and microstructure. Dynamic strain-aging phenomena were observed in Zircaloy at 200, 400, and 7000C, and superplastic deformation occurred at 850 and 10000C. An increase in the oxygen concentration in homogeneous Zircaloy-oxygen alloys increased the ultimate tensile strength and decreased the total strain, particularly below approximately 9000C. In composite specimens with the ZrO2/α/β structure, the total oxygen content had little effect on the ultimate tensile strength below approximately 10000C, but the strength increased with oxygen content at higher temperatures. Information on the effects of grain size, oxygen content, texture, and strain rate on the stress-strain behavior suggests that the dominant mechanism of superplastic deformation in Zircaloy near approximately 8500C is grain-boundary sliding at the α-β interface with accommodation by diffusional creep, dislocation slip, and grain-boundary migration. Good correlation was obtained between ductility and values of the strain-rate sensitivity parameter