Microstructure Stability and Mechanical Properties of Ultrafine-Grained Zirconium Alloy under Prolonged Thermal Exposure

The paper describes the experimental results in microstructure thermal stability and mechanical properties of ultrafine-grained zirconium alloy with 1 mass % Nb (Zr-1 mass % Nb) under prolonged thermal exposure. Ultrafine-grained zirconium alloy is produced by severe plastic deformation (SPD) method. It was proved that SPD method including multiple abc-pressing and multi-pass rolling, as well as further pre-recrystallizing annealing enhances the formation of ultrafine-grained structures with mean element size of 0.2 mu m. Thermostability time interval of ultrafine-grained structure and the mechanical properties (in case of microhardness) under prolonged thermal exposure (up to 360 hours) for zirconium alloy was experimentally determined. It was proved that ultrafine-grained structure is stable at 400 degrees C within 10 hours whilst keeping the microhardness level attained after SPD. In cases of continuous annealing time from 24 to 360 hours recrystallization processes develop intensively, followed by the decrease in microhardness and intensive growth of structure elements within the alloy.