铝和不锈钢中氦行为研究

【作者】 陈长安；

【导师】 孙颖；

【作者基本信息】 中国工程物理研究院北京研究生部 ， 核燃料循环与材料， 2003， 博士

【摘要】 针对放射性元素钚的α衰变引起的氦损伤问题，选择模拟材料铝进行了He的离子注入和其中氦行为的理论和实验研究，同时，也研究了氚工艺及聚变堆技术结构材料不锈钢中氚衰变~3He的扩散行为，从而对两种金属中He的行为有了较深入的认识。 在不锈钢氚衰变~3He的扩散行为研究中，建立了氚和~3He浓度分布的解析解和数值计算方法，以评估充氚不锈钢球形容器壁中氚衰变~3He的宏观浓度分布，同时还用数值计算方法以求解氚和~3He的多步扩散行为；对样品表面逐层蚀刻、同时收集释放的~3He进行分析，分别实测了经室温条件下在6.13MPa高压氚中贮存4年和6年、空气中存放3年和1年的两种21-6-9不锈钢球壳样品内壁中~3He浓度分布；结果表明：由于He在金属中的不可容性，He原子偏聚于不锈钢表面以及内部的局部区域，在整体趋势上，~3He分布与计算结果相一致，根据理论计算，两种21-6-9不锈钢球壳样品内壁中~3He到达的深度分别为350μm及500μm。 在金属铝中氦行为的理论研究中，基于密度泛函理论、广义梯度近似、赝势平面波方法，计算了单个He原子在金属铝中的各种能量数据，包括各种He原子-缺陷的形成能、迁移能、束缚能以及离解能数据。计算结果表明，晶内He原子择优占位区是空位，而在整个晶体范围，最有利于容纳He原子的区域是晶界，位错容纳He原子的能力次于晶界和空位；在fcc-铝的间隙位中，He原子优先充填四面体间隙位；晶内间隙He原子是可动的，通过间隙He原子的运动，可在晶内聚集，或被空位、晶界、位错等缺陷束缚。 在金属铝中氦行为的实验研究中，首先用离子注入技术在单晶、多晶以及择优取向的铝样品中引入不同能量、剂量和浓度分布的He原子，能量范围从50eV～4.87MeV，TRIM模拟的He浓度峰值的深度范围为16(?)～20.7μm，注入层的宽度为10(?)～1μm。其次，开展了氦行为的各项实验研究：增强质子背散射分析的结果表明，铝样品在注He的室温存放期间，He将发生扩散逃逸，120天后，大部分He原子逸出样品，其中由于缺乏晶界固He的作用，单晶铝中He的逃逸量更多；表面XRD分析的结果表明，铝样品注入He后，注入层将产生较小的畸变量，且畸变量与样品种类，He的注入和随后存放条件等因素有关，在同样注入和存放条件下，低指数、单晶铝的畸变量最大；表面慢正电子湮没谱的测量结果表明，S参数证实了注入层中He-空位缺陷的存在信息，经450℃以后高温的退火后，He-空位缺陷通过热扩散发生彼此问的融合而长大，使缺陷峰降低，而当退火温度低于350℃时，长大现象并不明显，同时进一步观察到He随存放时间向外逃逸的现象；表面纳米硬度测试的结果表明，He注入铝后，将引起铝的纳米硬度和弹性模量值的显著降低，使材料的强度下降，力学性能退化，且变坏的程度与He浓度和深度分布相对应；He的热解吸实验结果表明，50eV注He多晶铝只在80℃附近出现单一的低温解吸峰，且总的He量较少，60keV注He单晶铝和多晶铝的主要释放峰在4O0oC以后，通过求60keV注He单晶铝四个释放峰的激活能可知，He的热解吸过程对应于单个He原子从不同尺寸的空位团束缚态中的解离，但其过程比较复杂;表面形貌的SEM观察结果表明，铝样品注入He后，表面形貌会发生明显的改变:出现了溅射蚀坑、孔洞、鼓泡甚至表面层的剥落等现象，这些形貌与He+注入时的剂量、温度和能量等诸因素有关，其产生的机制与He+的溅射效应、内部氦泡的畸变并由此所产生的裂纹扩展机制相联系;注入层TEM的观察结果表明，内部氦泡的形态和分布与注入样品中的He浓度和注入时的温度，以及后期存放的时间和温度等因素有关，即使是室温、50eV的亚阂注入，高浓度的He注入层也会在内部发展成泡格子，而浓度和温度较低时，氦泡的长大不明显，当温度很高时，可以观察到不同尺寸的氦泡，较大的泡分布于缺陷处，并首次利用TEM电子束的热效应，在线观察了较大氦泡的长大过程，其主要以氦泡边界扩张的合并方式长大，而氦泡的直接迁移过程并不明显。更多还原

【Abstract】 Aimed at the helium damages in Plutonium caused by a decay, He+ ions were implanted in aluminum and the behaviors of helium in aluminum were investigated both theoretically and experimentally to simulate those effects in Plutonium. At the same time, the diffusion of helium-3 produced by tritium decay in stainless steels, which were served as the structural materials in tritium and fusion technologies, was also investigated in this thesis. The sense of this work is to gain a further understanding of helium in the two metals.On the diffusion of helium-3 in two spherical shell samples made of 21-6-9 type of stainless steel, during the storage of tritium at the pressure of 6.13MPa for about 4 and 6 years at room temperature and later exposed to air for another 3 and 1 year. First, a calculation based on the analytical and numerical method to the diffusion and decay theories was developed to evaluate the concentration distribution of helium-3 by tritium diffusion and decay in the samples. The numerical method was also used to solve the diffusion problem involved with several steps. By etching the inner surface with an acid solution and collecting the released helium-3 simultaneously and analyzing it later, the distribution of helium-3 in the shells was determined experimentally. Results showed that most helium-3 atoms were preferential segregated to the surface, and some accumulated at some local sites inward the shells. This is due to the incompatibility of helium with the matrix atoms. But on the whole, the trend of helium distribution by the determination was similar to that by calculation. And the depth which helium-3 could reach in both samples were 350 microns and 500 microns respectively.In the theoretical simulation on the behavior of single helium atom in aluminum, the varieties of energy data including the formation, migration, binding, and dissociation energies for single helium atom at the interstitial, vacancy, grain boundary, and dislocation sites in aluminum lattice were calculated, based on the density functional theories, general gradient approximation and pseudopotential plane wave method. Results showed that the most fittable sites for containing helium atoms inside the cell are vacancies. But in the view of the whole lattice, grain boundaries are the best. Dislocations can also contain helium with a relatively poorer ability than vacancies and grain boundaries. In the two interstitial sites in fcc-Al cell, He prefers to occupying the tetrahedron site. Helium interstitials are movable. It is easy for the accumulation of helium interstitials or being trapped by vacancies, grain boundaries and dislocations through the migration of helium interstitials.In the experimental studies on the behaviors of helium in aluminum, ion implantation technique was adopted to introduce helium with different energies, doses and distributions into some specimen of monocrystal, polycrystal, and preferred orientation as to the structure of aluminum. The energies varied in the range of 50eV to 4.87MeV. The corresponding helium peak depths by TRIM simulation varied in the range of 16 angstrom to 20.7 microns.The thickness of the helium layer varied in the range of 10 angstrom to 1 micron. Then varieties of methods were used to study the implanted helium in the specimen. Determination of the helium distribution by enhanced proton back scattering spectroscopy revealed that most helium has escaped out of the specimen during the long term of storage and the hugest loss by escape was found in the monocrystal aluminum which is lack of the grain boundaries for containing helium atoms. Lattice aberrance could be seen in the He+ implanted layers by small angular X-ray diffraction measurement. The largest swelling in the lattice parameter lies in the low index crystal face in monocrystal aluminum for the same implantation and storage process. S parameters in the slow positron annihilation spectroscopy denoted the distributions of helium-vacancy defects (HenVm) sensibly. Through annealing the samples above 450℃, he更多还原