正电子湮没谱学在金属材料氢/氦行为研究中的应用

Research progress of hydrogen/helium effects in metal materials by positron annihilation spectroscopy

用于核反应堆的金属结构材料中氢/氦泡的前躯体——(氢/氦)-空位复合体的形成受到温度、辐照剂量等多方面因素的影响,研究其在材料中的形成和演化行为对气泡形核的理解及先进核反应堆材料的发展起着至关重要的作用.然而,受到分辨率的局限,这种原子尺度的微结构很难用电镜等常规方法进行表征,以致于该问题的研究上可利用的数据相对较少.正电子湮没谱学是一种研究材料中微观缺陷的特色表征方法,近些年来慢正电子束流和新型核探测谱仪技术的不断发展以及基于慢束发展起来的多种实验测试方法的改进,使正电子湮没技术应用已拓展到金属材料中氢/氦行为的研究领域,在金属材料表面氢/氦辐照损伤的研究中发挥了重要作用.本文结合国内外相关进展以及本课题组的一些研究成果评述了正电子湮没谱学在金属材料氢氦行为研究中的应用,着重讨论了正电子湮没寿命谱、多普勒展宽谱、符合多普勒展宽三种测量方法在如下金属材料氢/氦行为研究中的优势:1)氢/氦气泡尺寸和浓度的估算;2)高能氢/氦离子辐照损伤缺陷及缺陷的退火、时效的演化行为;3)不同形变程度样品中氢/氦与形变缺陷的相互作用;4)不同能量或剂量氢/氦离子辐照对材料造成的损伤以及氢氦协同作用.

An important feature of the irradiation process in nuclear system is the formation of large displacement cascades,in which primary knock-on atoms and secondary particles formed by nuclear reactions generate a considerable number of defects such as dislocations,vacancies and transmutation gases.Predicting and mitigating the adverse effects of damage defect and transmutation hydrogen/helium produced by high-dose neutron irradiation on the mechanical properties of structural materials is the most significant challenge facing the current development of nuclear energy.To solve this problem,understanding the interaction mechanism between hydrogen/helium atoms and micro-defects is a very important breakthrough.Precursors of helium/hydrogen bubble,small helium/hydrogen-filled vacancy complexes,may play an important role in realizing bubble nucleation,and the formation of these complexes is affected by many factors.However,only a little information about helium/hydrogen-vacancy clusters’behavior has been obtained in metal/alloy materials.This is mainly limited by the characterization methods,such as the limited resolution of transmission electron microscope(TEM).Helium/hydrogen-vacancy clusters cannot be observed by TEM before the formation of helium bubbles.Applications of positron annihilation to the study of crystal lattice defects started around 1970s,when it was realized that positron annihilation is particularly sensitive to vacancy-type defects and that annihilation properties manifest the nature of each specific type of defect.In recent years,with the continuous development of slow positron beam and the improvement of various experimental testing methods based on slow positron beam,the application of positron annihilation technology has been extended to the research field of hydrogen/helium behavior in metal materials,which plays an important role in studying the hydrogen/helium radiation damage to metal materials.In this review,the basic principles of positron annihilation spectroscopy are briefly discussed and the three most important measurement methods used for hydrogen/helium effect studies are described(i.e.positron annihilation lifetime spectroscopy(PALS),Doppler broadening spectroscopy(DBS),coincidence Doppler broadening spectroscopy(CDBS)).In this paper,the application of positron annihilation spectroscopy to the study of hydrogen/helium behavior in metal materials is reviewed in combination with the reported relevant developments(including our research group’s achievements).The advantages of three commonly used measurement methods in the following specific studies are highlighted:1)The estimation of bubble size and concentration;2)irradiation damage induced by hydrogen/helium;3)the evolution behavior of irradiation-induced defects in the heat treatment process;4)synergistic effect of hydrogen and helium.