Global and local texture development during initial plastic deformation of cold-pilgered Zircaloy-4 tubing

GABRIEL JUAREZ; MIGUEL ANGEL VICENTE ALVAREZ; JAVIER R. SANTISTEBAN; JONATHAN ALMER; VLADIMIR LUZIN; PABLO VIZCAINO

JOURNAL OF NUCLEAR MATERIALS

ELSEVIER SCIENCE BV

Año: 2021 vol. 558 p. 1 - 15

0022-3115

This work presents a thorough characterization of the texture development during the initial step of a cold pilgering process of a Zircaloy-4 TREX tube, on which the axial cross section is reduced by 80% over a 40cm length with an overall Q-ratio of 2.34, followed by a recrystallization thermal treatment. Tex- ture across a tapered specimen representing this working zone was characterized by neutron diffraction and high energy synchrotron x-ray diffraction at 28 positions (4 locations along its length and 7 loca- tions across its thickness with 0.3 mm spatial resolution), and on the deformed end after the thermal treatment. Results show that the starting material (TREX tube) presents a texture gradient through its wall thick- ness, with the c poles aligned to the hoop direction at the outer surface (with radial and hoop Kearns factors: fR = 0.36, fH = 0.50), and gradually rotating around the axial direction to become a quasi-radial orientation ( ∼35 o out of the radial direction) at the inner surface ( fR = 0.43, f H = 0.35). The overall tex- ture becomes more radial due to the cold pilgering, but the texture gradient remains during the whole deformation process, being always more radial at the inner surface, ( fR = 0.53, fH = 0.37 at 80%) than at the outer surface ( fR = 0.41, fH = 0.50at 80%). The most remarkable changes in texture produced by the rolling process is a 30 o rotation of the grains around their c-axis, producing a marked increase of the < 11 ¯2 0 > // axial fiber texture at expenses of the original < 10 ¯1 0 > // axial fiber texture observed in the TREX tube. The observed changes in texture during deformation were correctly explained by visco-plastic self-consistent (VPSC) modelling. This was achieved after the inclusion of the basal < a > slip system, which plays a central role to explain the 30 o rotation around the c-axis during deformation. The texture evolution was correctly described after the inclusion of a drag effect to grain rotation due to the in- teraction with neighbouring grains. The through thickness texture differences are greatly reduced by the recrystallization thermal treatment, with similar Kearns factors at the inner surface ( fR = 0.50, fH = 0.28) and the outer surface ( fR = 0.48, fH = 0.39). The predominance of the < 10 ¯1 0 > // axial fiber texture is recovered after recrystallization.