Alternative TitleInvestigation of helium in Ti and Ti alloy
Thesis Advisor刘实
Degree Grantor中国科学院金属研究所
Place of Conferral金属研究所
Degree Discipline材料加工工程
Keyword 钛合金 纳米晶 热解析 分子动力学
Abstract核反应生成的氦在材料中的大量聚集会导致氦的释放、氦脆等问题。氦在材料中的独特行为还在半导体等多个领域有潜在应用。因此,氦在材料中的行为一直受到关注。本文以高固氦贮氢(氚)材料为背景,研究了氦在Ti及Ti合金中的存在。 在用磁控溅射方法向材料中引入氦的工作基础上,利用透射电镜表征了Ti、TiZr合金膜和TiMo合金膜的结构及氦的存在,发现合金膜由直径为20nm的晶粒构成,Ti膜由平均直径为100nm的晶粒组成,在退火后氦以氦泡的形式存在。发现氦泡可以为多面体形或球形,多数为球形化的多面体形,退火温度越高时间越长,氦泡越大,越接近多面体形。合金中的氦泡比纯Ti中的氦泡更接近球形,三叉晶界处的氦泡比在晶界处的氦泡更接近球形,两个氦泡靠近时近邻部分更接近球形。发现晶界是氦泡存在的有利位置,在界面、界线、界隅处的氦泡的稳定性依次增加。当材料的晶粒小于20nm,界隅会成为材料中稳定氦泡的主要势阱之一。发现在Ti中添加合金成份显著抑制了氦泡的生长。 对800℃热处理1小时后的含氦纯Ti膜做了热解析实验,发现存在有多个释放峰,各释放峰代表了受温度影响释放方式相似的一类氦。在匀速加热升温过程中,首先临近表面的氦开始释放,其次晶界和通向表面的位错处的氦分别开始释放,再次晶粒内部的氦开始释放。 利用第一原理计算研究了HCP Ti中的Ti-He作用。在Ti八面体间隙中心引入一个He原子,He原子与各个顶点Ti原子之间的相互作用差别不大,He原子与Ti原子间主要作用为排斥。由于Ti原子排列致密,经驰豫后He原子引起八面体间隙体积膨胀1/3,由于Ti-Ti键的方向性,各个顶点Ti原子的膨胀位移不同。 根据第一原理数据利用晶格反演法得到了FCC Ti-He体系的相互作用势,再现了He在材料晶格中的聚集现象,发现He原子聚集的原因是Ti-He排斥强于He-He,He原子通过合作的方式更容易取得存在空间。利用Møller-Plesset微扰理论计算得到的Ti-He相互作用势,较好的再现了He在Ti中的行为。
Other AbstractLarge amount of helium that produced in nuclear reactions gathering in materials can induce problems like helium releasing and materials embrittlement, which let devices failure. And many unique properties of helium in materials also have potential applications in areas such as semiconductor industry. Thus, the behavior of helium in materials has always been in focus. With background of highly helium retention hydrogen (tritium) storage materials, this paper focus on the behavior of helium in Ti and Ti alloy. Based on the previous work on introduction of helium into materials, the structures of Ti, TiZr alloy and TiMo film are characterized using a transmission electron microscopy. It is found that helium can be in form of bubbles in these materials after annealing. The shapes of helium bubbles can be spheres or polyhedrons while most are shperized polyhedrons. After annealing more time at higher temperature, the bubbles are more like polyhedrons. Bubbles in alloy are more round than those in pure Ti, and bubbles on triple grain boundary are more round than those on grain faces. When two bubbles get closed, the parts nearest each other usually become round, indicating their amalgamation. The positions of helium bubbles can be in grains and on grain junctions (boundaries), the energy is lower for bubbles on junctions of more grains, and the presence of helium bubbles can be greatly changed in nano materials due to high fraction of junctions of four above grains. The growth of helium bubbles in alloys is much inhibited, and TiZr alloy inhibit more than TiMo alloy. Many release peaks are found when applying thermal desorption on Ti film which contains helium and is annealed 1 hour at 800. It is considered that these release peaks ℃represent the helium releasing in different ways at temperatures. When heating at a constant velocity, the helium nearby the surface starts to release firstly; then the helium on grain boundaries and diclocations which are helium pipeline to surface, and next the 中国科学院金属研究所硕士学位论文 Ti 及 Ti 合金中氦的存在研究 III helium of no pipeline to surface. Ab initio calculations are employed to study the lattice swelling of a Ti atom. It is found the interactions between an octahedral He atom and its first coordination Ti atoms are almost the same when the distances are equal, and are mainly rejection. Due to the short distances between Ti-Ti atoms in HCP Ti, a He atom can swell an octahedral interstice 1/3 in volume, and due to the orientating feature of Ti-Ti interaction, Ti atoms nearest a He atom at the centre octahedral interstice are rejected to different distances. The interaction potentials of a FCC Ti-He system are attained employing lattice inverse method. The potentials physically reproduce the gathering phenomenon of helium in materials. It was found helium gathering because of Ti-He rejection is stronger than He-He rejection, and when more He atoms coordinate each other, they can get spaces more easily. Another Ti-He two body interaction potential is attained through Møller–Plesset perturbation calculation, which reproduce the helium phenomenon in HCP Ti quite well when employed with an EAM Ti-Ti potential.
Document Type学位论文
Recommended Citation
GB/T 7714
刘本良. Ti及Ti合金中氦的存在研究[D]. 金属研究所. 中国科学院金属研究所,2007.
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