Creep Properties and Microstructure of Commercially Pure Zirconium at Ambient Temperature

The creep tests were carried out on commercially pure zirconium (CP-Zr) in different states under the stresses of 0.9R(P0.2), 0.925R(P0.2), 0.95R(P0.2) and 0.975R(P0.2) at ambient temperature (AT). Their steady state creep rate and creep stress were calculated. The microstructures of CP-Zr before and after annealing and creep tests were analyzed. The results indicate that the threshold stress of CP-Zr in different states exists in creep tests at AT. When the creep stress is greater than the threshold stress value, the density of dislocation of CP-Zr obviously increases with the increase of creep stress, and the significant dislocation pile-up can be observed at grain boundaries. It is found that the UFG CP-Zr after annealing at 250 degrees C can not only maintain grain size and stable microstructure, but also keep the original high strength and improve the plasticity compared with CG CP-Zr. In addition, the annealing treatment at 250 degrees C can improve the creep properties of UFG CP Zr, weaken the creep stress sensitivity and enhance the creep resistance.