Modelling the Effect of Texture and Dislocation Structure on Irradiation Creep of Zirconium Alloys

Abstract

The effect of texture and dislocation structure on irradiation creep of Zircaloy-2 (irradiated at about 340 K) and Zr-2.5 wt% Nb alloys (irradiated at about 558 K) is studied by means of a self-consistent model. The model relates the creep behaviour of polycrystals to that of single crystals by taking into account the crystallographic texture, dislocation density, grain shape and the intergranular stresses generated due to the crystallographic anisotropy. Three independent creep compliances of the polycrystal obtained from creep tests on a reference material are used to derive the single crystal creep compliances. These are used to calculate the polycrystalline compliances for the remaining materials. At low irradiation temperatures the predicted polycrystalline compliances agree well with the measured values. The observed behaviour can be described by a climb-assisted glide mechanism in which the creep strain is accommodated mainly by prismatic slip with smaller contributions from basal and pyramidal slip systems. At higher irradiation temperatures, the self-consistent approach can also describe well the creep behaviour of Zr-2.5 wt% Nb samples.

Anisotropic thermal creep of internally pressurized Zr–2.5Nb tubes

“…Crystals deforming by slip are, hence, substantially stronger along the c-axis than in the basal plane, a situation that leads qualitatively to the variation in ( _ e A = _ e T ) versus (f T À f R ) seen in Fig. 12 [11]. Another factor that could affect the anisotropy from slip is the distribution of different dislocation types from cold work amongst the different grain orientations, as seen by Griffiths et al [2].…”

“…In a previous study of in-reactor deformation, Zr-2.5Nb tubes were only available with a few different crystallographic textures in which basal plane normals are concentrated in the transverse or radial direction [11,12]. This significantly restricts the understanding of the relationship between crystallographic texture and anisotropic creep.…”

The effect of stress on point-defect diffusion in hcp metals and irradiation creep

“…Therefore we can assume that » c º 0 in this case. Calculated single-crystal irradiation creep compliance rates from three model interatomic potentials, in comparison with those determined from experimental creep data via polycrystalline models (Woo 1987b, Christodoulou et al 1993. It is clear that the variability between the calculated results from the di erent potentials is large.…”

Influence of prior dislocation structure on anisotropy of thermal creep of cold-worked Zr–2.5Nb tubes

“…Crystallographic texture is an important factor controlling creep anisotropy. However, because a limited range of textures is available for this material, the relationship between texture and anisotropic creep is not fully understood [3][4][5]. This limitation also restricts the development and evaluation of new anisotropic creep models.…”

“…This limitation also restricts the development and evaluation of new anisotropic creep models. Several versions of a self-consistent polycrystalline model, SELFPOLY, have been used to calculate the steady-state creep anisotropy of pressure tube materials for CANDU reactors [3][4][5][6]. In all versions, the model assumes that all crystal orientations have the same response to stress and thus crystallographic texture is the only factor determining anisotropy in thermal and irradiation and creep.…”