【作者】 唐维维；

【导师】 何维均；

【作者基本信息】 重庆大学 ， 工程（材料工程）（专业学位）， 2020， 硕士

【摘要】 由于其较低的中子吸收截面、优异的耐腐蚀性以及力学性能,锆及其合金作为结构件被广泛应用在核反应堆和化学工业中。由于其典型的(α+β)双相组织及优异的耐腐蚀性能、综合力学性能等特点,Zr-Nb合金备受关注。本文以民用版的Zr-2.5Nb合金(Zr705)为研究对象,开展不同工艺的热、机械处理,以调控其微观组织、优化其力学性能。利用SEM、EBSD、XRD以及TEM等表征技术表征微观组织,基于维氏硬度及压缩实验分析力学性能演变,研究了轧制变形温度对后续退火组织及力学性能的影响规律及机制,探讨了压缩变形对淬火试样时效组织及力学性能的影响规律及机制。针对原始态Zr705合金,开展了室温以及液氮温度条件下的轧制变形,以及200℃～700℃温度范围内的后续退火处理。轧制变形过程中,Zr705合金中的(α+β-Zr)两相区内的片层状α相与β-Zr相随变形量增大逐渐平行于轧制方向。退火过程中,随着退火温度的升高,Zr705合金的硬度与强度先升高后降低,先升高的原因主要是因为析出了细小弥散的ω粒子,而回复与再结晶导致了硬度与强度的降低。在相同变形量与退火温度条件下,液氮轧制样品的峰值时效强度与硬度要高于室温轧制样品,这可能是因为液氮温度抑制了动态回复,保留的位错密度更高,导致β-Zr→ω转变驱动力更大,析出了更多的ω粒子所致。针对原始态Zr705合金,开展了650℃～850℃温度范围内的固溶处理,并针对部分温度淬火试样开展了不同变形量的压缩变形以及不同温度与时间的后续时效处理。在固溶处理中,随着固溶温度升高,更多的Nb原子固溶在基体中,导致屈服强度显著增加。淬火+压缩变形+时效处理组织为三态组织,即α呈三种不同的形貌,分别为初始等轴α_p相、厚片层状α_t和薄片层α。随着压缩变形量的增加,初生α_p相逐渐减少,更多β-Zr从α’相析出,β-Zr粗化速度越快。时效过程中,预压缩样品的强度与硬度随时间的增加单调降低,而无预变形的样品则是先升高后降低。当时效温度较低时(550℃),β-Nb呈颗粒状析出。当时效温度较高时(650℃),β-Zr主要以片层状形式析出。相同变形量以及相同时效时间条件下,经550℃时效后试样的屈服强度高于650℃时效试样。更多还原

【Abstract】 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(α+β)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 lamellarαphase andβ-Zr phase in the(α+β-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 dispersedωparticles.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.Theβ-Zr→ωtransformation driving force is greater,and moreωparticles 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 whichαphase has three different morphologies:primary equiaxedα_pphase,thick lamellarα_tand thin lamellar layerα.As the increase of the compression,the primary equiaxedα_pphase gradually decreases,and moreβ-Zr precipitates from theα’phase,and theβ-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℃),β-Nb precipitates in the form of particles.When the aging temperature is high(650℃),β-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℃.更多还原