【作者】 万鹏；

【导师】 栾佰峰；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2024， 硕士

【摘要】 锆合金由于良好的中子经济性、优良的耐腐蚀性等优点,在核反应堆中主要用作核燃料包壳材料。目前,核反应堆技术主要向高燃耗、长周期等方向发展,这对锆合金的使役性能提出了更高的要求。锆合金的性能与退火等工艺密切相关,本文以我国自主研发的新型Zr-Sn合金为研究对象,系统地研究了退火温度与时间对轧制态锆合金的微观组织与力学性能的影响规律。主要研究内容与结果如下:首先,采用SEM、EBSD以及TEM等技术研究了冷轧锆合金板材退火过程的微观组织演变规律。结果表明,冷轧板材中存在高位错密度的变形组织,在低温退火(430℃、530℃)过程中,位错发生滑移与攀移,形成低位错密度的亚结构;高温退火(630℃)时,合金组织中出现再结晶晶粒的形核与长大,随着退火时间的延长,再结晶分数逐渐增加,退火3 h后,合金再结晶分数只有约53.7%,未充分再结晶。冷轧板材中析出相数量较少且主要呈流线分布特征,退火处理后析出相数量增多、尺寸增大、呈弥散分布。受轧制等加工工艺影响,冷轧板材晶粒取向为基面双峰织构特征,其中晶粒的<0001>方向在RD(轧向)-ND(法向)平面,并偏向RD方向约20°,且大部分晶粒的<101?0>方向平行于RD方向。退火过程中,晶粒c轴向ND方向偏转,导致晶粒c轴在ND方向周围分布,且晶粒绕其c轴旋转30°,导致{0001}<101?0>织构向{0001}<112?0>织构转变。其次,采用单轴拉伸实验测试了合金板材沿RD方向与TD方向的极限抗拉强度、屈服强度和断裂延伸率。结果表明,冷轧与退火板材屈服强度存在明显的各向异性。冷轧后沿TD方向拉伸试样的屈服强度(626.4 MPa)高于沿RD方向拉伸试样(598.9 MPa)。退火后,RD试样与TD试样的强度降低,塑性增加,TD试样的屈服强度仍高于RD试样。分析发现,TD试样主要滑移系(柱面<a>滑移)的SF=0.4～0.5的占比(27%～42%)低于RD试样(70%～78%)最后,采用XRD测量了热处理前后合金板材的残余应力,并结合相应微观组织表征,阐述了残余应力降低机理。结果表明,冷轧板材存在104.8±18.9 MPa残余压应力,430℃、530℃退火1 h时,高能量的原子与空位向平衡位置迁移导致应力松弛,残余压应力分别降至73.6±2.3 MPa与71.2±2.9 MPa,延长退火时间(430℃/3 h、530℃/2 h),位错通过滑移与攀移形成低位错能量的亚结构,应力降至41.6±7.7 MPa与34.5±4.0 MPa。630℃退火1 h时,不仅有原子与空位的迁移,还存在再结晶晶粒的形核与长大,残余压应力降低至64.4±11.4 MPa,延长退火时间,再结晶分数增加,残余应力降低,在退火3 h后,应力降低至26.1±5.4 MPa。更多还原

【Abstract】 Zirconium alloy is mainly used as nuclear fuel cladding material in nuclear reactors due to its excellent neutron economy and corrosion resistance.At present,nuclear reactor technology is mainly developing towards high fuel consumption and long cycles,which puts higher requirements on the service performance of zirconium alloys.The properties of zirconium alloys are closely related to the annealing and other processes,this article takes the newly developed Zr-Sn alloy in China as the research object,and systematically studies the influence of the annealing temperature and time on the microstructure and mechanical properties of rolled zirconium alloys.The main research contents and results are as follows:Firstly,the microstructure evolution of cold-rolled zirconium alloy sheets during annealing was studied using techniques such as SEM,EBSD and TEM.The results show that there is a deformation structure with high dislocation density in the cold-rolled sheet.During low-temperature annealing(430℃,530℃),dislocations slip and climb to form a substructure with low dislocation density;during high-temperature annealing(630℃),nucleation and growth of recrystallized grains appear in the alloy structure.With the extension of the annealing time,the recrystallization fraction gradually increases.After 3hours of annealing,the recrystallization fraction of the alloy is only about 53.7%,which is not fully recrystallized.The number of precipitates in the cold-rolled sheet is relatively small and mainly exhibits a streamline distribution feature,After annealing treatment,the number and size of precipitates increase,showing a dispersed distribution.Due to the influence of processing techniques such as rolling,the grain orientation of cold-rolled sheets exhibits a basal bimodal texture feature,where the<101?0>direction of the grains is in the RD(rolling)-ND(normal)plane,and is inclined towards the RD direction by about 20°,with most grains<101?0>direction is parallel to the RD direction.During the annealing process,the c-axis of grains deviates in the ND direction,causing the c-axis of grains to be distributed around the ND direction,and the grains rotate 30°around their c-axis,resulting in{0001}<101?0>texture direction{0001}<112?0>texture transformation.Secondly,the ultimate tensile strength,yield strength,and fracture elongation of the alloy sheet along the RD and TD directions were tested using uniaxial tensile experiments.The results indicate that there is a significant anisotropy in the yield strength of cold-rolled and annealed sheets.The yield strength of the tensile specimen along the TD direction after cold rolling(626.4 MPa)is higher than that of the tensile specimen along the RD direction(598.9 MPa).After annealing,the strength of the RD and TD specimens decreased,plasticity increased,and the yield strength of the TD specimen remained higher than that of the RD specimen.Analysis shows that the proportion of SF=0.4～0.5(27%～42%)in the main slip system(prismatic<a>slip)of TD samples is lower than that of RD samples(70%～78%)Finally,the residual stress of the alloy sheet before and after heat treatment was measured using XRD,and the corresponding microstructure characterization was combined to elucidate the mechanism of residual stress reduction.The results showed that there was a residual compressive stress of 104.8±18.9 MPa in the cold-rolled sheet.When annealed at 430℃and 530℃for 1 hour,high-energy atoms and vacancies migrated to the equilibrium position,leading to stress relaxation.The residual compressive stress decreased to 73.6±2.3 MPa and 71.2±2.9 MPa,respectively.The annealing time was extended(430℃/3 h and 530℃/2 h),and dislocations formed a substructure with low dislocation energy through slip and climb,resulting in stress reduction to 41.6±7.7 MPa and 34.5±4.0 MPa,respectively.When annealed at 630℃for 1 hour,not only the migration of atoms and vacancies,but also the nucleation and growth of recrystallized grains.The residual compressive stress decreases to 64.4±11.4MPa.Extending the annealing time increases the recrystallization fraction,and the residual stress decreases.After annealing for 3 hours,the stress decreases to 26.1±5.4MPa.更多还原