摘要
为了研究Zr对钇合金铸态组织结构、元素分布和维氏硬度的影响,本文使用磁悬浮感应熔炼,对钇合金进行5次熔炼,得到成分偏差小于0.3%、杂质含量低于0.05%、表面质量好的钇合金铸锭。采用X射线衍射(XRD)对合金的物相结构进行标定,随着Zr含量的添加,合金中α-Zr的特征峰逐渐明显,且Y在铸态合金中显示出了固溶度的扩展,对α-Y的晶格参数进行计算,得到室温下Zr在铸态合金中的极限固溶度,约为4%(质量分数)。使用光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)对合金的组织进行分析,当Zr的含量小于5%时,钇锆合金组织由简单的等轴晶组成;当Zr的含量大于5%时,晶界处有共晶组织出现。随着Zr含量的增加,晶粒尺寸逐渐减小,说明Zr对Y合金有显著的晶粒细化的作用。经EDS检测,元素Zr主要在晶界位置分布。使用数显维氏硬度计对材料的维氏硬度进行测量,发现当Zr的添加量为1%~20%时,合金元素Zr的添加会增强钇合金的维氏硬度。
Since 1960s,many countries leaded by the United States and Russia have done a lot of researches on the space nuclear reactor power.Moderator is an important functional component in nuclear reactor operating with a thermal neutron spectrum.Due to the limitation of volume and mass,metal hydride is usually used as moderator in small reactor.Since the second half of the 20th century,zirconium hydride has been the main hydride used as moderator material for small nuclear reactor,but it has the disadvantages of short life and low working temperature.Compared with zirconium hydride,yttrium hydride has stronger thermal stability and is suitable for long life and high power small nuclear reactor.In order to prolong the life of small nuclear reactor and increase its power,it is necessary to study and fabricate yttrium hydrate matrix.Pure yttrium or yttrium-based alloy was the raw material for the preparation of yttrium hydride moderator.It’s composition,microstructure and performance directly affected the performance of hydride moderator.In order to provide possible quality yttrium alloy for manufacturing hydride moderator and study the effect of Zr on the structure,element distribution and Vickers hardness of as-cast yttrium alloy,magnetic levitation induction melting method was employed to yttrium-zirconium alloys with Zr content of 1%,5%,10%,20%were prepared which remelt for five times.The yttrium alloy with smooth surface were obtained with the component deviation less than 0.3%,impurity content less than 0.05%.X-ray diffraction(XRD)was used to calibrate the phase structure of the alloy.With the increase of zirconium content,the characteristic peak of Zr in the alloy became more and more obvious.Y showed the solid expansion in the as-cast alloy.The lattice parameters ofα-Y were calculated by XRD and the ultimate solid solubility of Zr in cast alloy at room temperature was about 4%.Optical microscope(OM),scanning electron microscope(SEM)and energy dispersive spectrometer(EDS)were used to analyze the microstructure of the alloy,and it was found that when the content of Zr was less than 5%,the yttrium zirconium alloy structure was composed of simple isometric crystal.When the content of Zr was more than 5%,the eutectic organization appeared in the grain boundary.With the increase of Zr content,the grain size gradually decreased.Indicating that Zr had a significant role in grain refinement of Y alloy after detection by EDS,the element Zr was mainly precipitated in the grain boundaries and played a role of refining the grains.Digital display Vickers hardness tester was used to measure the Vickers hardness of the material.It was found that the addition of Zr increased the Vickers hardness of yttrium alloy when the addition of Zr was 1%~20%.Forging,heat treatment,surface processing,hydrogenation and other processes were needed from yttrium-based alloy to yttrium hydride.Therefore,the following research also needed to focus on:(1)The forging performance of yttriumbased alloys.In order to select suitable yttrium-based alloys,the forging temperature,pressure and deformation speed of the yttriumbased alloy was required to obtain the stress-strain curve of the yttrium-based alloy.The quality of the hydrogenated material was determined by the quality of the matrix.(2)Considering whether the forging needed to be performed under protective gas conditions,and the oxidation resistance of yttrium-based alloys at different temperatures and time needed to be obtained,the oxidation weight gain law of yttrium-based alloys could be obtained from the oxidation weight gain curve.(3)To obtain the pressure-composition-temperature curve of the yttrium-based alloy at 700~900℃through experiment,and analyze the performance of yttrium hydride and to observe the alloy structure and element distribution after hydrogenation,provide a basis for the selection of the optimal system moderator,and provide theoretical support for the subsequent preparation of yttrium hydride.The design of future moderator materials needed to focus on the following two aspects:(1)Further improve the thermal stability of moderator materials.The lager the temperature difference between the inlet and outlet of the coolant,the better the improvement of the power supply,the current operating temperature greatly limited the maximum temperature.Such working temperature could not meet future power demand of the space nuclear reactor.Increasing the thermal stability of the moderator material could not only achieve higher power requirements,but also ensure the safety of nuclear reactors and extend the service life.(2)Reduce the volume of moderator and compact the core structure.Compared with slow neutron spectrum reactors,the advantage of fast neutron spectrum reactors was the high utilization rate of nuclear fuel.In thermal neutron spectrum reactors,more structural materials were used,and the critical mass of nuclear fuel was higher.Some neutrons were absorbed during the movement,which reduced the utilization rate of nuclear fuel.Therefore,reducing the volume of moderators and compacting the core structure were the most direct ways to improve fuel utilization.In addition,in the selection of moderator cores and core materials,preferential selection of elements with smaller neutron absorption cross-sections was also conducive to improving fuel utilization.
作者
刘芳辰
王智辉
闫国庆
袁学韬
王力军
Liu Fangchen;Wang Zhihui;Yan Guoqing;Yuan Xuetao;Wang Lijun(National Engineering Laboratory of Biohydrometallury,GRINM Engineering Institute Co.,Ltd,,Beijing 101407,China;China GRINM Resources and Environment Tech.Co.,Ltd,Beijing 100088,China;General Research Institute for Nonferrous Metals,Beijing 100088,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2022年第3期315-323,共9页
Chinese Journal of Rare Metals
基金
国家自然科学基金项目(51674035)资助。
关键词
钇锆合金
铸态组织
固溶度
细化晶粒
维氏硬度
yttrium zirconium alloy
as-cast structure
solid solubility
refined grain
Vickers hardness
