鋯合金中的氫氦行為研究
發(fā)布時間：2018-07-29 21:02
【摘要】：鋯合金由于其較低的熱中子吸收截面,良好的力學和耐腐蝕性能,能夠很好地與核燃料(U02)相容等優(yōu)點而廣泛應(yīng)用于裂變核能系統(tǒng)。其在服役過程中會與氫以及微量的氦發(fā)生相互作用,從而引起結(jié)構(gòu)和性能上的變化,降低了它的安全性和使用壽命。鋯-氫體系本身的復(fù)雜性給研究帶來了很大困難,目前對鋯氫化物各個不同相的穩(wěn)定性以及相互之間相轉(zhuǎn)變的認識仍存在分歧。此外,外界因素如熱處理狀態(tài),應(yīng)力,第二相的尺寸、分布、結(jié)構(gòu)和組成等都會對鋯氫化物的形成產(chǎn)生影響。一般認為,少量氦對鋯合金結(jié)構(gòu)和性能的影響幾乎可以忽略不計,但在特定環(huán)境下,鋯合金中形成的氦的量會增加到必須予以重視的程度,目前這方面的研究還很匱乏。 本論文針對現(xiàn)有研究中重點關(guān)注而仍未得到深入研究的問題從理論和實驗兩個方面研究了氫氦對純鋯和國產(chǎn)N18合金的結(jié)構(gòu)和性能的影響,試圖為改進現(xiàn)有鋯合金抗氫脆、氦脆的性能提供參考。主要研究了不同氫化物相的相對穩(wěn)定性、相轉(zhuǎn)變隨氫含量變化的規(guī)律；第二相與氫的相互作用；釔元素的摻雜對氫化物形成的影響；高壓扭轉(zhuǎn)對氫化物形成的影響；氦對鋯的結(jié)構(gòu)和力學性能的影響。 采用第一性原理軟件VASP結(jié)合SQS(Special Quasirandom Structures)建模方法研究了氫化物的有序相和無序相。研究發(fā)現(xiàn),對于氫化物的有序相,ζ-Zr2H、“金剛石型”γ-ZrH、δ-[111]以及fcc結(jié)構(gòu)的ZrH2都是不穩(wěn)定的。而對于氫化物的無序相,隨著H濃度的增加,Zr-H體系逐漸從hcp向fcc,然后繼續(xù)向fct(c/a1)結(jié)構(gòu)轉(zhuǎn)變。其中hcp(固溶體)和δ相之間的平衡態(tài)介于ZrHo.25和ZrH0.375之間,δ相和ε相之間的平衡態(tài)的組成介于ZrH和ZrH1.s之間。從能量角度看,γ相在各個H濃度下都是不穩(wěn)定的。 采用第一性原理軟件VASP結(jié)合SQS建模方法研究了第二相與氫的相互作用。首先考察了簡單的二元ZrCr2體系,在其中7種不同的四面體間隙位中,H占據(jù)H5-2Zr2Cr型的間隙位的形成能最低。除了H2-4Cr型間隙,H占據(jù)其他間隙位的形成能均小于0。其次,重點研究了較復(fù)雜的贗二元Zr(FexCr1-x)2體系,發(fā)現(xiàn)隨著Fe濃度的增加,其晶格常數(shù)和體模量均呈線性降低。H占據(jù)Zr(Fe0.5Cr0.5)2中的H5-2Zr2Cr型四面體間隙位的形成能最低。且晶胞中的Fe原子越多,越不利于H的吸收。而無論是出現(xiàn)Zr、Fe還是Cr原子的離位,相比于完整晶體,H進入這些四面體間隙的形成能均更低。 采用光學顯微鏡、掃描電鏡、透射電鏡、X射線衍射儀等方法研究了摻雜Y元素對鋯合金結(jié)構(gòu)和性能的影響。發(fā)現(xiàn)摻Y(jié)的N18合金在氫化后,既有晶粒內(nèi)又有晶粒間氫化物形成,但氫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。在這些部分氧化的Y顆粒的周圍,發(fā)現(xiàn)氫化物的富集生長的現(xiàn)象。 采用光學顯微鏡、納米壓痕儀、透射電鏡、X射線衍射儀、二次離子質(zhì)譜(SIMS)等方法研究了高壓扭轉(zhuǎn)對鋯合金結(jié)構(gòu)和性能的影響。發(fā)現(xiàn)經(jīng)高壓扭轉(zhuǎn)處理后,N18和N18+Y合金樣品中均沒有出現(xiàn)ω和β相的鋯。維氏硬度均有所上升,升高的幅度約為10%。高壓扭轉(zhuǎn)處理后氫化物出現(xiàn)聚集生長并聯(lián)接呈網(wǎng)狀的現(xiàn)象。第二相的EDS和SIMS結(jié)果均顯示,Fe的分布變化不大,而部分Cr向基體中擴散。第一性原理計算的結(jié)果表明,第二相中Fe的結(jié)合力要比Cr大,Cr更容易向基體擴散并在原晶格位置留下空位,從而導(dǎo)致氫的聚集。 采用第一性原理軟件CASTEP研究了He對鋯的結(jié)構(gòu)和性能的影響。結(jié)果表明,對于無缺陷的a-Zr晶格,從能量角度來看,He最傾向于占據(jù)·BO位置,而對于已存在空位的a-Zr晶格,He位于S位時體系最穩(wěn)定。He的引入會以各向異性的方式改變體系的彈性常數(shù),使得彈性各向異性顯著增加。當He與空位結(jié)合成He-V團簇時,這種效應(yīng)會得到增強,從而使得Zr的力學性能顯著惡化。使用SRIM程序計算得到,200KeV的氦離子注入到鋯后,形成的損傷的峰值深度為600-650nm,氦濃度的峰值深度在700nm左右,其中1017ions/cm2的注量下,氦的濃度為0.78%左右,離位損傷約為4dpa。使用納米壓痕儀測量了氦離子注入樣品的顯微硬度和彈性模量,發(fā)現(xiàn)隨著氦離子注量的增加,純Zr和N18合金的顯微硬度均明顯增大,純Zr的彈性模量略有下降,而N18合金的彈性模量明顯下降。 上述研究結(jié)果進一步揭示了在反應(yīng)堆使役環(huán)境下鋯合金中復(fù)雜的氫氦行為,得到了鋯氫化物不同相的相對穩(wěn)定性以及鋯氫化物各物相之間的相轉(zhuǎn)變隨氫含量變化的趨勢,獲得了第二相與氫、鋯與氦之間的相互作用對鋯及其合金結(jié)構(gòu)和性能的影響規(guī)律,提出了摻雜釔元素以及經(jīng)高壓扭轉(zhuǎn)處理后氫化物聚集生長的機理。本論文的研究工作為改進現(xiàn)有鋯合金抗氫脆、氦脆的性能提供了較系統(tǒng)的科學認識和技術(shù)支持,也為其他材料中的氫氦行為,特別是對未來聚變堆結(jié)構(gòu)材料中氫氦協(xié)同效應(yīng)的研究具有方法學意義。
[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.
【學位授予單位】：中國科學技術(shù)大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TG146.414
本文編號：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.
【學位授予單位】：中國科學技術(shù)大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TG146.414
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相關(guān)期刊論文 前2條
1 彭德全,白新德,潘峰,孫輝;純鋯上離子注入釔和鑭后的表面分析[J];物理學報;2005年12期
2 范開敏;楊莉;孫慶強;代云雅;彭述明;龍興貴;周曉松;祖小濤;;六角相ErA_x(A=H,He)體系彈性性質(zhì)的第一性原理研究[J];物理學報;2013年11期
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