Pilgering of Zircaloy-4: Experiments and simulations

The evolution of crystallographic texture during pilgering of Zircaloy-4 was studied experimentally and determined using crystal plasticity simulations. The pilgered samples showed a characteristic texture with 0 0 0 2 poles aligned away from the circumferential direction towards the axial as well as the radial direction. The texture remained similar but weakened on further annealing. The evolution of residual stresses was recorded at the macroscopic (type III) as well as microscopic (type II intergranular and type I intragranular) level. Crystal plasticity simulations indicated that the high stresses involved during pilgering enabled the activity of basal slip at room temperature in Zircaloy-4. It has been shown that high intergranular type II stresses are most deleterious for pilgering and limit the amount of strain achieved in a single step. It is therefore, proposed that reduction in type II stresses by process modification can help in reducing number of steps in processing of Zircaloy-4 tubes.