注氢纯铝中间隙型位错环一维迁移现象的原位观察

In-situ study of one-dimensional motion of interstitial-type dislocation loops in hydrogen-ion-implanted aluminum

核聚变堆材料在高能粒子辐照过程中会产生大量点缺陷,导致辐照脆性和辐照肿胀等现象.因而,研究点缺陷在辐照过程中的演变过程至关重要.点缺陷团簇的一维迁移现象是这种演变过程的主要研究内容之一.本文采用普通低压(200 kV)透射电镜,在室温条件下对注氢纯铝中的间隙型位错环在电子辐照下的一维迁移现象进行了观察和分析.在200 keV电子辐照下,注氢纯铝中的位错环可多个、同时发生一维迁移运动,也可单个、独立进行一维迁移运动.位错环沿柏氏矢量1/3<111>的方向可进行微米尺度的一维长程迁移,沿柏氏矢量1/2<110>的方向一维迁移也可达数百纳米.电子束辐照时产生的间隙原子浓度梯度是引起位错环一维迁移并决定其迁移方向的原因.位错环发生快速一维迁移时,其后会留下一条运动轨迹;位错环一维迁移的速率越快,运动的轨迹则越长,在完成迁移过后的几十秒内这些运动轨迹会逐渐消失.

The one-dimensional(1D) glide motion of dislocation loops along the direction of Burgers vector in various metallic materials has attracted considerable attention in recent years.During the operation of nuclear fusion reactor,component materials will be bombarded by high energy neutrons,resulting in production of radiation defects such as self-interstitial-atoms(SIAs),vacancies and their clusters.These defects feature large difference in migration energy,which may lead to concentration imbalance between SIAs and vacancies,and eventually irradiation damages such as swelling and embrittlement.Generally speaking,the mobility of a defect cluster is lower than that of a point defect.However,fast 1D motion may also take place among SIA clusters in the form of prismatic dislocation loops.This increases the transport efficiency of SIAs towards grain boundaries,surface and interface sites in the material,in favour of defect concentration imbalance and damage accumulation.To date,most literature works have found that the 1D motion of dislocation loops exhibited short-range(nanometer-scale) character.In addition,such experimental studies were generally conducted in pure metals using high voltage electron microscopes(HVEM) operated at acceleration voltages ≥1000 kV.However,for pure aluminum(Al),the maximum transferable kinetic energy from 200 keV electrons is 19.5 eV,while the displacement threshold energy is only 16 eV.Therefore,the observation and mechanistic investigation of 1D motion of dislocation loops in Al should also be possible with conventional transmission electron microscopes(C-TEM),as it may also exhibit the effects of beam heating and point defect production in HVEM.In view of the shortage of HVEM,this work reports the 1D motion of dislocation loops in pure Al implanted with hydrogen ions using C-TEM.Simultaneous dislocation loop motion in opposite directions of Burgers vector 1/2<110>has been captured,as well as the collective 1D motion of an array of dislocation loops in the direction of Burgers vector 1/3<111> under 200 keV electron irradiation.In addition,1D motion of dislocation loops up to micron-scale range along the direction of Burgers vector 1/3<111>,and up to a few hundred nanometers range along the direction of Burgers vector 1/2<110> have been found,which is different from previous literature works.A characteristic migration track would form behind the moving dislocation loop,lasting for about tens of seconds.The more rapid the dislocation loop motion,the longer the migration track length is.The concentration gradient of SIAs by electron irradiation and the redistribution of hydrogen atoms caused by the moving dislocation loops may account for the observed micron-scale 1D motion of dislocation loops and the migration tracks.