Microstructural and Textural Evolution of a Zr-Sn-Nb-Fe Alloy Tube During Cold Pilger Rolling

In this study, a cold-pilgered Zr alloy tube with the composition of Zr-1.0 wt%Sn-1.0 wt%Nb-0.3 wt%Fe was investigated. During the cold pilgering, the tube developed distinct microstructural and textural features at different positions (with varying internal/external diameters and wall thicknesses) due to their specific stress states and deformation amount. Microstructural and textural evolution during cold pilgering were analyzed by characterizing specimens (S0-S4) cut from typical tube positions mainly using electron channeling contrast imaging and electron backscatter diffraction techniques. Transmission electron microscopy was also utilized to reveal typical precipitates in the un-pilgered specimen (S0). Results indicate that at low/medium strains, there exist non-deformation grains with hard orientations in the pilgered tube specimens, leading to heterogeneous microstructures. With increasing strains, the tube specimens show continuously reduced grain sizes and increased kernel average misorientations along with higher fractions of low angle boundaries, resulting in enhanced microstructural homogeneity. During the pilgering, the texture of Zr-1.0Sn-1.0Nb-0.3Fe alloy tube gradually transforms from initial c//TD to c//RD, which changes back to the c//TD at high strains (>similar to 60%). In the meantime, the < 10-10>//AD component is initially weakened slightly but then significantly enhanced, while there is an opposite trend for that of the < 11-20>//AD component. According to the analysis of in-grain misorientation axes, the textural evolution during the pilgering results from the coordination of multiple slip systems and the pyramidal slip can be substantially activated at a high strain.