Effect Of Pre-deformation On The Microstructure And Properties Of Annealed Zr705 Alloy

Zirconium(Zr)and its alloys are widely used as structural parts in nuclear reactors and chemical industries,due to its low neutron absorption cross-section,excellent corrosion resistance and mechanical properties.Because of its typical(?+?)two-phase structure,excellent corrosion resistance and comprehensive mechanical properties,Zr-Nb alloy has attracted extensive attention.This paper takes the civilian version of Zr-2.5Nb alloy(Zr705)as the experimental material,and carries out various thermal and mechanical treatments to tailor its microstructure and optimize its mechanical properties.Using SEM,EBSD,XRD and TEM techniques,the microstructures are characterized.The mechanical properties are analyzed based on Vickers hardness testing and compression experiments.This paper reveals the effect of rolling temperature on the subsequent annealing structure and mechanical properties,and discusses the influence of compression deformation on the evolution of aged microstructure and mechanical properties.For the original Zr705 alloy,rolling at room temperature and liquid nitrogen temperature are carried out,followed by subsequent annealing treatment within the temperature range of 200?to 700?.During the rolling,the lamellar?phase and?-Zr phase in the(?+?-Zr)two-phase zone are gradually parallel to the rolling direction with the increase of the applied amount of deformation.During the annealing process,as the annealing temperature increases,the hardness and strength of the Zr705alloy first increase and then decrease.The reason for the first increase is mainly due to the precipitation of fine and dispersed?particles.While,the recovery and recrystallization lead to hardness and strength reduction.Under the same deformation and annealing temperature conditions,the peak aging strength and hardness of the liquid nitrogen rolled samples is higher than those of the room temperature rolled samples.This may be because the liquid nitrogen temperature represses the dynamic recovery and the retained dislocation density is higher.The?-Zr??transformation driving force is greater,and more?particles are precipitated.For the original Zr705 alloy,solid solution at temperature range of 650?to850?are carried out.Compressions are also performed for some of the quenched samples,which are followed by ageing at different temperatures and for different holding time.During the solid solution process,with the solid solution temperature increasing,more Nb atoms are dissolved in the matrix,leading to the significant increase of yield strength.The microstructure of quenched+compression+aging treatment is a three-states structure,in which?phase has three different morphologies:primary equiaxed?_pphase,thick lamellar?_tand thin lamellar layer?.As the increase of the compression,the primary equiaxed?_pphase gradually decreases,and more?-Zr precipitates from the?'phase,and the?-Zr coarsening rate is faster.During the aging process,the strength and hardness of the compressed samples decrease monotonically with aging time,while the samples without deformation first increase and then decrease.When the aging temperature is low(550?),?-Nb precipitates in the form of particles.When the aging temperature is high(650?),?-Zr is mainly precipitated in the form of lamellae.Under the same deformation and aging time,the yield strength of the sample aged at 550?is higher than that of the sample aged at 650?.