Grain refinement of commercially pure zirconium by ECAP and subsequent intermediate heat treatment

Microstructural evolution of commercially pure zirconium (Zr702) processed by equal channel angular pressing (ECAP) and subsequent intermediate heat treatment was investigated. ECAP was carried out at room temperature, and the sample was rotated 90° in the same sense in each pass. Also, intermediate heat treatment of the ECAP samples processed by was performed at 773 and 873 K for their recovery and recrystallization temperatures. When the samples were annealed at recrystallization temperature of 873 K, the mean grain size of these samples decreased from ∼40 to ∼3 μm by the further four passes of ECAP. However, when the samples were annealed at recovery temperature of 773 K, the mean grain size was found to be 0.2 μm after the same ECAP process. A difference in microstructural evolution with annealing processes indicated that the rate of formation of new grains for ultra-fine-grained Zr702 was accelerated due to the high fraction of subgrains into the matrix of Zr702 after recovery.