锆合金中的氢氦行为研究
发布时间：2018-07-29 21:02
【摘要】：锆合金由于其较低的热中子吸收截面,良好的力学和耐腐蚀性能,能够很好地与核燃料(U02)相容等优点而广泛应用于裂变核能系统。其在服役过程中会与氢以及微量的氦发生相互作用,从而引起结构和性能上的变化,降低了它的安全性和使用寿命。锆-氢体系本身的复杂性给研究带来了很大困难,目前对锆氢化物各个不同相的稳定性以及相互之间相转变的认识仍存在分歧。此外,外界因素如热处理状态,应力,第二相的尺寸、分布、结构和组成等都会对锆氢化物的形成产生影响。一般认为,少量氦对锆合金结构和性能的影响几乎可以忽略不计,但在特定环境下,锆合金中形成的氦的量会增加到必须予以重视的程度,目前这方面的研究还很匮乏。 本论文针对现有研究中重点关注而仍未得到深入研究的问题从理论和实验两个方面研究了氢氦对纯锆和国产N18合金的结构和性能的影响,试图为改进现有锆合金抗氢脆、氦脆的性能提供参考。主要研究了不同氢化物相的相对稳定性、相转变随氢含量变化的规律；第二相与氢的相互作用；钇元素的掺杂对氢化物形成的影响；高压扭转对氢化物形成的影响；氦对锆的结构和力学性能的影响。 采用第一性原理软件VASP结合SQS(Special Quasirandom Structures)建模方法研究了氢化物的有序相和无序相。研究发现,对于氢化物的有序相,ζ-Zr2H、“金刚石型”γ-ZrH、δ-[111]以及fcc结构的ZrH2都是不稳定的。而对于氢化物的无序相,随着H浓度的增加,Zr-H体系逐渐从hcp向fcc,然后继续向fct(c/a1)结构转变。其中hcp(固溶体)和δ相之间的平衡态介于ZrHo.25和ZrH0.375之间,δ相和ε相之间的平衡态的组成介于ZrH和ZrH1.s之间。从能量角度看,γ相在各个H浓度下都是不稳定的。 采用第一性原理软件VASP结合SQS建模方法研究了第二相与氢的相互作用。首先考察了简单的二元ZrCr2体系,在其中7种不同的四面体间隙位中,H占据H5-2Zr2Cr型的间隙位的形成能最低。除了H2-4Cr型间隙,H占据其他间隙位的形成能均小于0。其次,重点研究了较复杂的赝二元Zr(FexCr1-x)2体系,发现随着Fe浓度的增加,其晶格常数和体模量均呈线性降低。H占据Zr(Fe0.5Cr0.5)2中的H5-2Zr2Cr型四面体间隙位的形成能最低。且晶胞中的Fe原子越多,越不利于H的吸收。而无论是出现Zr、Fe还是Cr原子的离位,相比于完整晶体,H进入这些四面体间隙的形成能均更低。 采用光学显微镜、扫描电镜、透射电镜、X射线衍射仪等方法研究了掺杂Y元素对锆合金结构和性能的影响。发现掺Y的N18合金在氢化后,既有晶粒内又有晶粒间氢化物形成,但氢化物的尺寸有所增大。N18合金中的第二相主要有Zr(Fe,Cr)2和Zr(Fe,Cr,Nb)2,N18+Y合金中的第二相主要有Zr(Fe,Cr)2和部分氧化的Y。在这些部分氧化的Y颗粒的周围,发现氢化物的富集生长的现象。 采用光学显微镜、纳米压痕仪、透射电镜、X射线衍射仪、二次离子质谱(SIMS)等方法研究了高压扭转对锆合金结构和性能的影响。发现经高压扭转处理后,N18和N18+Y合金样品中均没有出现ω和β相的锆。维氏硬度均有所上升,升高的幅度约为10%。高压扭转处理后氢化物出现聚集生长并联接呈网状的现象。第二相的EDS和SIMS结果均显示,Fe的分布变化不大,而部分Cr向基体中扩散。第一性原理计算的结果表明,第二相中Fe的结合力要比Cr大,Cr更容易向基体扩散并在原晶格位置留下空位,从而导致氢的聚集。 采用第一性原理软件CASTEP研究了He对锆的结构和性能的影响。结果表明,对于无缺陷的a-Zr晶格,从能量角度来看,He最倾向于占据·BO位置,而对于已存在空位的a-Zr晶格,He位于S位时体系最稳定。He的引入会以各向异性的方式改变体系的弹性常数,使得弹性各向异性显著增加。当He与空位结合成He-V团簇时,这种效应会得到增强,从而使得Zr的力学性能显著恶化。使用SRIM程序计算得到,200KeV的氦离子注入到锆后,形成的损伤的峰值深度为600-650nm,氦浓度的峰值深度在700nm左右,其中1017ions/cm2的注量下,氦的浓度为0.78%左右,离位损伤约为4dpa。使用纳米压痕仪测量了氦离子注入样品的显微硬度和弹性模量,发现随着氦离子注量的增加,纯Zr和N18合金的显微硬度均明显增大,纯Zr的弹性模量略有下降,而N18合金的弹性模量明显下降。 上述研究结果进一步揭示了在反应堆使役环境下锆合金中复杂的氢氦行为,得到了锆氢化物不同相的相对稳定性以及锆氢化物各物相之间的相转变随氢含量变化的趋势,获得了第二相与氢、锆与氦之间的相互作用对锆及其合金结构和性能的影响规律,提出了掺杂钇元素以及经高压扭转处理后氢化物聚集生长的机理。本论文的研究工作为改进现有锆合金抗氢脆、氦脆的性能提供了较系统的科学认识和技术支持,也为其他材料中的氢氦行为,特别是对未来聚变堆结构材料中氢氦协同效应的研究具有方法学意义。
[Abstract]:Zirconium alloy is widely used in the fission nuclear energy system because of its low thermal neutron absorption cross section, good mechanical and corrosion resistance and good compatibility with nuclear fuel (U02). It will interact with hydrogen and trace helium in the service process, which leads to structural and performance changes and reduces its safety. The complexity of the zirconium hydrogen system itself has brought great difficulties to the research of the zirconium hydrogen system. At present, there are still differences in the stability of the different phases of the zirconium hydride and the phase transition between each other. In addition, the external factors such as heat treatment, stress, the size, distribution, structure and composition of the second phase are formed for the formation of zirconium hydrides. It is generally believed that the effect of a small amount of helium on the structure and properties of zirconium alloys is almost negligible, but in a specific environment the amount of helium formed in the zirconium alloy will increase to the extent that it must be paid attention to, and the research in this respect is still very scarce.
This paper studies the effect of hydrogen helium on the structure and properties of pure zirconium and homemade N18 alloy from two aspects of theory and experiment, which is the key concern in the existing research and still has not been studied in depth. The purpose of this study is to provide a reference for improving the properties of hydrogen brittleness and helium embrittlement of the existing zirconium alloys. The change in the phase change with the hydrogen content; the interaction of the second phase with the hydrogen; the effect of the doping of Yttrium on the formation of hydride; the effect of the high pressure torsion on the formation of hydride; the effect of helium on the structure and mechanical properties of zirconium.
The ordered phase and disordered phase of the hydride are studied by the first principle software VASP and the SQS (Special Quasirandom Structures) modeling method. It is found that the ordered phase of the hydride, the zeta -Zr2H, the "diamond" gamma -ZrH, the delta -[111], and the ZrH2 of the fcc structure are unstable. For the disorder phase of the hydride, with the H concentration In addition, the Zr-H system gradually moves from HCP to FCC, and then continues to transform to the FCT (c/a1) structure. The equilibrium state between HCP (solid solution) and delta phase is between ZrHo.25 and ZrH0.375, and the equilibrium state between the Delta and epsilon phases is between ZrH and ZrH1.s. From the energy point of view, the phase of gamma is unstable at every H concentration.
The interaction between second phases and hydrogen is studied with the first principle software VASP and the SQS modeling method. First, a simple two element ZrCr2 system is investigated. In the 7 different tetrahedron spaces, the formation of the H5-2Zr2Cr type gap is the lowest in the 7 different tetrahedron spaces. In addition to the H2-4Cr gap, the formation of the H occupying other space positions can be less than 0.. At the same time, the more complex pseudo two element Zr (FexCr1-x) 2 system was studied. It was found that with the increase of Fe concentration, the lattice constant and the bulk modulus showed a linear decrease in the formation of the H5-2Zr2Cr type tetrahedron space position in Zr (Fe0.5Cr0.5) 2, and the more Fe atoms in the cell were not favorable for the absorption of H, but no matter Zr, Fe or Cr. Compared with the complete crystal, the formation energy of H entering these tetrahedral gaps is lower.
The effects of doped Y elements on the structure and properties of zirconium alloys were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X ray diffractometer. It was found that after hydrogenating, Y doped N18 alloys have both grain and intergrain hydrides, but the size of the hydride is larger than Zr (Fe, Cr) 2 and Zr (Fe, Fe,). Cr, Nb) 2, the secondary phase in the N18+Y alloy is mainly Zr (Fe, Cr) 2 and partially oxidized Y. around these partially oxidized Y particles, and the enrichment and growth of the hydride is found.
The effects of high pressure torsion on the structure and properties of zirconium alloys were studied by optical microscopy, nano indentation, transmission electron microscopy, X ray diffractometer and two ion mass spectrometry (SIMS). It was found that after high pressure torsion treatment, no omega and beta phase zirconium was found in N18 and N18+Y alloy samples. The hardness of Vivtorinox increased, and the increase was about 10. The results of EDS and SIMS in the second phase show that the distribution of Fe has little change and the partial Cr diffuses into the matrix. The results of the first principle calculation show that the binding force of Fe is larger than that of Cr in the second phase, and Cr is more easily diffused to the matrix and left in the original lattice position. The vacancy, which leads to the accumulation of hydrogen.
The effect of He on the structure and properties of zirconium is studied by the first principle software CASTEP. The results show that, for the amorphous a-Zr lattice, from the energy point of view, He tends to occupy the position of. BO, and for the a-Zr lattice with existing vacancies, the introduction of the most stable.He in the He at the S bit will change the system's projectile in an anisotropic manner. The properties of the elastic anisotropy increase significantly. When the He and the vacancies are combined into a He-V cluster, the effect is enhanced and the mechanical properties of the Zr are significantly deteriorated. The SRIM program is used to calculate the 200KeV helium ion implanted into the zirconium, and the peak depth of the damage is 600-650nm and the peak depth of the helium concentration is around 700nm. Under the injection of 1017ions/cm2, the concentration of helium is about 0.78%. The microhardness and modulus of elasticity of helium ion implantation samples are measured by 4dpa. using nanoindentation. It is found that the microhardness of pure Zr and N18 alloy increases obviously with the increase of helium ion injection, and the modulus of elasticity of pure Zr decreases slightly, while N18 alloy's elastic modulus is reduced. The modulus of sex decreased obviously.
The above results further reveal the complex hydrogen helium behavior in the zirconium alloy under the causation of the reactor, obtain the relative stability of the different phases of the zirconium hydride and the change of the phase transition between the phases of the zirconium hydride, and obtain the structure of the zirconium and its alloy structure between the second phase and the hydrogen, the zirconium and the helium. The mechanism of the doping of yttrium elements and the accumulation of hydride after high pressure torsion treatment is proposed. The research work of this paper provides a systematic scientific understanding and technical support for improving the hydrogen embrittlement and helium embrittlement of the existing zirconium alloys, and the behavior of hydrogen and helium in other materials, especially for the future fusion reactor junction. The study of synergetic effect of hydrogen and helium in structural materials is of methodological significance.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.414
本文编号：2154009
[Abstract]:Zirconium alloy is widely used in the fission nuclear energy system because of its low thermal neutron absorption cross section, good mechanical and corrosion resistance and good compatibility with nuclear fuel (U02). It will interact with hydrogen and trace helium in the service process, which leads to structural and performance changes and reduces its safety. The complexity of the zirconium hydrogen system itself has brought great difficulties to the research of the zirconium hydrogen system. At present, there are still differences in the stability of the different phases of the zirconium hydride and the phase transition between each other. In addition, the external factors such as heat treatment, stress, the size, distribution, structure and composition of the second phase are formed for the formation of zirconium hydrides. It is generally believed that the effect of a small amount of helium on the structure and properties of zirconium alloys is almost negligible, but in a specific environment the amount of helium formed in the zirconium alloy will increase to the extent that it must be paid attention to, and the research in this respect is still very scarce.
This paper studies the effect of hydrogen helium on the structure and properties of pure zirconium and homemade N18 alloy from two aspects of theory and experiment, which is the key concern in the existing research and still has not been studied in depth. The purpose of this study is to provide a reference for improving the properties of hydrogen brittleness and helium embrittlement of the existing zirconium alloys. The change in the phase change with the hydrogen content; the interaction of the second phase with the hydrogen; the effect of the doping of Yttrium on the formation of hydride; the effect of the high pressure torsion on the formation of hydride; the effect of helium on the structure and mechanical properties of zirconium.
The ordered phase and disordered phase of the hydride are studied by the first principle software VASP and the SQS (Special Quasirandom Structures) modeling method. It is found that the ordered phase of the hydride, the zeta -Zr2H, the "diamond" gamma -ZrH, the delta -[111], and the ZrH2 of the fcc structure are unstable. For the disorder phase of the hydride, with the H concentration In addition, the Zr-H system gradually moves from HCP to FCC, and then continues to transform to the FCT (c/a1) structure. The equilibrium state between HCP (solid solution) and delta phase is between ZrHo.25 and ZrH0.375, and the equilibrium state between the Delta and epsilon phases is between ZrH and ZrH1.s. From the energy point of view, the phase of gamma is unstable at every H concentration.
The interaction between second phases and hydrogen is studied with the first principle software VASP and the SQS modeling method. First, a simple two element ZrCr2 system is investigated. In the 7 different tetrahedron spaces, the formation of the H5-2Zr2Cr type gap is the lowest in the 7 different tetrahedron spaces. In addition to the H2-4Cr gap, the formation of the H occupying other space positions can be less than 0.. At the same time, the more complex pseudo two element Zr (FexCr1-x) 2 system was studied. It was found that with the increase of Fe concentration, the lattice constant and the bulk modulus showed a linear decrease in the formation of the H5-2Zr2Cr type tetrahedron space position in Zr (Fe0.5Cr0.5) 2, and the more Fe atoms in the cell were not favorable for the absorption of H, but no matter Zr, Fe or Cr. Compared with the complete crystal, the formation energy of H entering these tetrahedral gaps is lower.
The effects of doped Y elements on the structure and properties of zirconium alloys were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X ray diffractometer. It was found that after hydrogenating, Y doped N18 alloys have both grain and intergrain hydrides, but the size of the hydride is larger than Zr (Fe, Cr) 2 and Zr (Fe, Fe,). Cr, Nb) 2, the secondary phase in the N18+Y alloy is mainly Zr (Fe, Cr) 2 and partially oxidized Y. around these partially oxidized Y particles, and the enrichment and growth of the hydride is found.
The effects of high pressure torsion on the structure and properties of zirconium alloys were studied by optical microscopy, nano indentation, transmission electron microscopy, X ray diffractometer and two ion mass spectrometry (SIMS). It was found that after high pressure torsion treatment, no omega and beta phase zirconium was found in N18 and N18+Y alloy samples. The hardness of Vivtorinox increased, and the increase was about 10. The results of EDS and SIMS in the second phase show that the distribution of Fe has little change and the partial Cr diffuses into the matrix. The results of the first principle calculation show that the binding force of Fe is larger than that of Cr in the second phase, and Cr is more easily diffused to the matrix and left in the original lattice position. The vacancy, which leads to the accumulation of hydrogen.
The effect of He on the structure and properties of zirconium is studied by the first principle software CASTEP. The results show that, for the amorphous a-Zr lattice, from the energy point of view, He tends to occupy the position of. BO, and for the a-Zr lattice with existing vacancies, the introduction of the most stable.He in the He at the S bit will change the system's projectile in an anisotropic manner. The properties of the elastic anisotropy increase significantly. When the He and the vacancies are combined into a He-V cluster, the effect is enhanced and the mechanical properties of the Zr are significantly deteriorated. The SRIM program is used to calculate the 200KeV helium ion implanted into the zirconium, and the peak depth of the damage is 600-650nm and the peak depth of the helium concentration is around 700nm. Under the injection of 1017ions/cm2, the concentration of helium is about 0.78%. The microhardness and modulus of elasticity of helium ion implantation samples are measured by 4dpa. using nanoindentation. It is found that the microhardness of pure Zr and N18 alloy increases obviously with the increase of helium ion injection, and the modulus of elasticity of pure Zr decreases slightly, while N18 alloy's elastic modulus is reduced. The modulus of sex decreased obviously.
The above results further reveal the complex hydrogen helium behavior in the zirconium alloy under the causation of the reactor, obtain the relative stability of the different phases of the zirconium hydride and the change of the phase transition between the phases of the zirconium hydride, and obtain the structure of the zirconium and its alloy structure between the second phase and the hydrogen, the zirconium and the helium. The mechanism of the doping of yttrium elements and the accumulation of hydride after high pressure torsion treatment is proposed. The research work of this paper provides a systematic scientific understanding and technical support for improving the hydrogen embrittlement and helium embrittlement of the existing zirconium alloys, and the behavior of hydrogen and helium in other materials, especially for the future fusion reactor junction. The study of synergetic effect of hydrogen and helium in structural materials is of methodological significance.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.414
【参考文献】
相关期刊论文 前2条
1 彭德全,白新德,潘峰,孙辉;纯锆上离子注入钇和镧后的表面分析[J];物理学报;2005年12期
2 范开敏;杨莉;孙庆强;代云雅;彭述明;龙兴贵;周晓松;祖小涛;;六角相ErA_x(A=H,He)体系弹性性质的第一性原理研究[J];物理学报;2013年11期
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