金属中氢致空位形成机制研究

Vacancy is one of the most common defects in metals and has great influence on both structure and properties of material. The equilibrium concentration of vacancies in metal is extremely low, but vacancies can be produced, by such as irradiation of high energy particles. However, hydrogen bubble is observed under hydrogen irradiation with quite low energy in tungsten, which is related with vacancies. Thus, vacancy is believed to be induced by the retained hydrogen during low energy irradiation in tungsten. The vacancy formation mechanism under such conditions remains a great issue to be resolved. Considered as one of the most promising plasma facing material (PFM) to be used in fusion devices, the vacancy formation mechanism in W-PFMs and other metals will be studied. The structures of self-interstitial atoms (SIAs) clusters related to vacancy formation will also be discussed. Using molecular dynamics (MD) simulations with our self-developed W-H potentials, we plan to simulate the process of hydrogen induced vacancy formation in tungsten under different conditions. The influence of different defects, such as surface, grain boundary and impurities like He atoms on vacancy formation will also be considered. We will use the first-principles calculations combined with possible TEM experiments to further investigate the structures of SIAs clusters obtained with the appearance of vacancies. And in order to get the general rules of vacancy formation in metals, we plan to do similar research on the the vacancy formation process in other metals like bcc metal iron and fcc metal nickel.

空位是金属中常见缺陷之一，与金属材料结构和性能密切相关。金属中空位平衡浓度极低，但一些外界因素如高能粒子辐照可导致空位产生。有趣的是实验中观测到金属钨在极低能量氢辐照下产生了起泡现象，由于氢泡成核与空位紧密相关，可推断低能辐照下因滞留而存在于钨体内的氢亦可导致空位产生。该情况下空位产生机制作为一个重要问题尚无研究，亟需解决。本项目以聚变用体心立方钨基面对等离子体材料为主要研究对象，系统研究金属中氢致空位形成机制。初期研究表明空位形成与钨中一种自间隙原子团紧密相关。利用自行开发的钨氢原子间作用势，采用分子动力学方法模拟在氢存在的情况下钨中空位形成的条件和过程，考察表面、晶界和杂质如氦等对空位形成的影响；结合第一原理方法与可能的透射电镜实验，深入研究自间隙原子团与空位形成的联系和规律。并由此进一步研究其它金属如体心立方金属铁和面心立方金属镍中氢致空位形成，以期获得金属中氢致空位形成的一般规律。

空位是常见于金属中的一种缺陷，它对金属材料结构和性能有很大影响。一般情况下，金属中空位平衡浓度极低，但存在一些外界因素时，空位浓度会较高，如高能粒子辐照产生大量空位。有趣的是实验中观测到金属钨(W)在极低能量氢辐照下也产生了起泡现象，由于氢泡成核与空位紧密相关，可推断低能辐照下因滞留而存在于钨体内的氢亦可导致空位产生。然而，空位产生机制作为一个重要问题尚无研究，亟需解决。针对该问题，本项目的研究思路是从W中氢扩散行为，氢与缺陷相互作用等方面的研究，来探索氢致空位形成机制。采用分子动力学和第一原理方法的模拟研究，揭示了H在W体内及W表面的扩散机制；揭示了W中不同氢浓度条件下氢致空位形成机制，给出了与空位形成相关的自间隙原子团簇结构；弄清了W中空位团簇在H原子的作用下长大的过程，也即氢泡在W中长大的过程；揭示了W近表面层空位的形成机制以及W表面层空位对H的捕获作用；揭示了空位等缺陷对钨[100] 倾转对称晶界耦合运动的机制，弄清了空位向[100]倾转对称晶界偏析的形为。探索H对Frenkel缺陷形成及复合的影响，揭示了H作用下Frenkel缺陷形成与复合机制。更进一步，通过建立热力学模型定量预测了W中不同温度和压强下氢致空位形成氢泡的临界氢浓度，取得了与实验相符合的结果，为通过控制 H 浓度对钨基材料的等离子体辐照进行抑制提供了重要的参考。通过本项目的研究揭示了金属本征W中、存在不同缺陷（表面，晶界等）体系中的氢致空位形成机制。