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This paper summarizes our recent work on thin sheets, thick-walled TREXs, and thin-walled tubings of Zircaloy materials with emphasis on texture analyses, orientation distribution functions, plasticity models, correlation of single crystal behavior to textured bulk materials as well as their application to in-reactor performance of cladding materials in LWRs. The mechanical anisotropy and strain localization were investigated on recrystallized Zircaloy-4 sheet using the grid method, which yielded the transverse contractile strain ratios (R,P), formability parameter B, critical strains to necking, and fracture. The anisotropy and formability parameters were also evaluated from texture data and crystallite orientation distribution function (CODF) using prism slip as the dominant deformation mode, and both the lower bound and Bishop-Hill analyses were considered. Excellent correlations were noted between the experimental results and lower bound model predictions.
Constant strain-rate impression tests were used to evaluate the directional dependence of the mechanical characteristics of recrystallized Zircaloy-2 TREX from which the mechanical anisotropy and formability parameters were derived. The poor correlation between the experimental results and plasticity-CODF model predictions is attributed to the large texture gradients of the thick-walled tube shells. These parameters determined at the mid-wall using the grid method, however, correlated excellently with the prism model.
Biaxial creep of cladding materials is considered in terms of creep loci at constant energy dissipation for CWSR Zircaloy-4 along with the results by Stehle et al. on recrystallized Zircaloy-4 and by Suzuki et al. on Zircaloy-2. Moreover, the anisotropic yield locus developed for Zircaloy-2 by Suzuki et al. is also considered. The minor compositional differences between the two alloys have negligible influences on their textures as well as their creep behaviors, and all of these results on the recrystallized materials agreed with the predicted creep locus based on prism slip. Quantitative correlations were made by appropriately adjusting the creep compliance. The creep behavior of CWSR cladding was quite different from the recrystallized and correlated with the assumption of basal slip dominance.
The application of creep anisotropy derived from CODF in predicting the out-of-pile and in-pile creep behaviors of fuel rod cladding is demonstrated by considering appropriate model equations for thermal and radiation creep components as well as radiation growth developed by Murty et al., Wilson et al., and Clevinger et al.
zirconium alloys, sheet, tube-reduced extrusion, cladding, anisotropy, creep, formability, impression, deformation, texture, slip, crystallite orientation, distribution function, recrystallization, radiation, plasticity, growth
Professor, North Carolina State University, Raleigh, NC