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Extremes of anisotropic multiaxial creep behaviors were considered by analyzing the strain rate ratios versus applied stress ratio for highly cold-worked stress-relieved and partially recrystallized Zircaloy-4 tubings. Power-law creep was modeled by using the upper-bound estimate with the assumption that prism, basal, and pyramidal slip modes are possible mechanisms. Experimental strain rate ratios were compared with those calculated by statistical averaging of crystallite behavior using the crystallite orientation distribution function (CODF). The experimental data on the stress-relieved material were in excellent agreement with the model predictions based on basal slip as the dominant deformation mode. Data on partially recrystallized material were in reasonable agreement with the predictions based on a combination of basal and prism slip modes.
These results are also correlated with the Von-Mises—Hill phenomenological description with appropriate contractile strain ratios (anisotropy parameters), R and P. The parameter R is relatively insensitive to partial recrystallization and is related to the basal pole angle. The P-parameter, however, is shown to be very sensitive to fabrication procedures and is greater than unity for well-annealed material with split prism pole distributions. As the amount of cold work increased, P-parameter decreased to well below unity.
zirconium alloys, multiaxial deformation, creep, anisotropy, texture, annealing, slip, crystallite orientation, distribution function, strain ratios
Associate Professor, North Carolina State University, Raleigh, N.C.
Assistant Professor, University of Florida, Gainesville, Fla.