Evolution of texture and intergranular stresses of αZr and minority phases in Zr-2.5Nb pressure tube through synchrotron X-ray diffraction

Abstract

This study investigates the impact of different processing steps on the crystallographic texture evolution of αZr and minority phases βZr and ωZr, and intergranular stresses as a function of grain orientation in a Zr2.5Nb pressure tube. This was done by analysis of diffraction data recorded in the 1-ID line of the Advanced Photon Source for high energy X-Rays (∼80 Kev) in transmission geometry on three samples with different processing conditions: extruded, cold rolled and after autoclaving. The crystallographic texture of both αZr and βZr phases changes slightly after cold rolling, with the Burgers orientation relationship between the two phases remaining intact. The texture of βZr and ωZr shows that βZr decomposition during thermal treatment is sensitive to grain orientation. A new method was proposed to obtain the orientation dependence of the intergranular stresses from the experimental pole figures. Intergranular stresses in αZr grains were low after extrusion, but rolling significantly increased them, with values with magnitude as higher as 350 MPa and a strong dependence on grain orientation. The autoclaving treatment leads to important stress relaxation, but the dependence on grain orientation remains. The βZr phase grains exhibit significant intergranular strains in both extruded and cold-rolled conditions; the hydrostatic part was associated to the presence of Nb in solid solution, with content of ∼20 % and an orientation dependence of approximately ±1 at%. The deviatoric strain was attributed to intergranular stresses, with stresses below 80 MPa for the extruded sample and ranging from −600 to 400 MPa after cold rolling.