Studies On Irradiation Defects Of Metal Materials And Heterogeneous Interfaces

Non-renewable sources of energy are encountering continuous decrease in natural reserve.It is urgent to develop alternative options of renewable energy,such as nuclear energy.The fusion reaction of light elements in nuclear energy has attracted increasing attention because of its renewable and pollution-free advantages.The magnetic confinement method,as the most promising solution,can be used to promote the formation of controllable nuclear fusion.This method is implemented via the "International Thermonuclear Experimental Reactor" program.However,in order to implement controlled nuclear fusion,we also need to consider the problem of reactor material performance.During the operation of fusion reactor,nuclear materials will be irradiated by various high-energy particles,resulting in irradiation defects,irradiation swelling,and irradiation hardening,which will lead to material failure:It is very important to study in-depth the production and annihilation of irradiation defects in metal materials and heterogeneous interfaces.This thesis mainly dealt with these problems in three different aspects.During irradiation,various types of defects,such as dislocation loops and voids,could form in reduced activation ferritic/martensitic(RAFM)steels.Among these defects,dislocation loops serve as a major type of defect sink,and their interstitial/vacancy nature have important effects on material properties.For example,irradiation hardening is mainly related to the accumulation of interstitialtype dislocation loops,while vacancy-type dislocation loops are one of the main reasons for irradiation swelling.However,the interstitial loops were mainly identified and concerned in most studies,and few studies were focused on vacancy loops in iron-based alloys.In particular,there are fewer studies on the synergistic effect of hydrogen and alloying elements on vacancy-type dislocation loops in ironbased alloys.In part I,the formation temperature and influencing factors of vacancy loops in iron-based alloys after hydrogen ion implantation were studied.On one hand,the formation of large vacancy loops in hydrogen pre-implanted Fe-1.4 wt.%Mn(Fe-1.4Mn)was investigated by high voltage electron microscopes(HVEM).The irradiated Fe-1.4Mn alloy was annealed at 500℃ by HVEM,and then the in-situ observation was carried out under electron radiation.According to the dynamic growth/shrinkage behaviour of dislocation loops under electron irradiation,the nature of dislocation loops was revealed.It was found that the formation temperature of vacancy loops in Fe-Mn alloy was>500℃.This means that the addition of Mn in α-Fe could increase the formation temperature of vacancy loops.On the other hand,due to the limitations in availability for most HVEM facilities,an alternative method via 200 kV transmission electron microscope(TEM)has been introduced,and proven effective in cross checking the conclusions gained from HVEM.Post-irradiation annealing of hydrogen pre-implanted specimens(αFe,Fe-3Cr,Fe-1.4Ni,Fe-1.4Mn)at different temperatures would result in variations in loop size and population,which could deduce estimates of the formation temperature of vacancy loops.In aspects of fundamental study,this work may shed light on the correlation between hydrogen and evolution of dislocation loop behaviour,demonstrate the effects of minor alloying with low activation Mn and provide a new criterion in classifying common alloying elements(Cr,Mn etc)found in RAFM steel.The new criterion essentially incorporates the synergistic effect between displacement damage and hydrogen,and will provide a more accurate prediction of material response to swelling.The one-dimensional(1D)motion of defect clusters is an efficient transport mechanism of irradiated defects.The generation and migration efficiency of point defects and clusters are increased due to the 1D motion of dislocation loops during irradiation,which leads to irradiation damage in the material.In order to explore the formation mechanism and migration direction of dislocation loops,part II of this thesis focused on their 1D motion in Al,pre-implanted with 30 keV H+ions,and characterized in situ under 200 kV electron irradiation.Micron-scale 1D motion of dislocation loops was discovered for the first time in metal materials by in-situ TEM observations.During electron irradiation,1D motion left behind long-lasting tracks up to 60 s while the average speeds were over 1nm/s.The more rapid the loop motion,the longer length of the migration track was.The concentration gradient of interstitial atoms along the direction of Burgers vector induced by electron irradiation is the direct reason for 1D motion of dislocation loops.Therefore,1D motion of dislocation loops is essentially the migration process of dislocation loops from the region with high concentration of point defects to the region with low concentration.Through the study of 1D motion of dislocation loops,the physical mechanism of 1D motion is revealed,and a clear understanding of the evolution process of point defects and clusters in metal materials during irradiation is obtained.In view of the problems of tritium permeation and material corrosion faced by the cladding structural materials of fusion reactors,our group proposed a"Vanadium alloy(V-4Cr-4Ti)/Ti/AlN" composite insulating coating in the early stage,and the interface microstructure and bonding strength of the V-4Cr-4Ti/Ti were analyzed,while the properties after irradiation were not studied.And on that basis,the irradiation damage of heavy nuclear ions at the heterogeneous interface of V-4Cr-4Ti/Ti and their interaction with the interface were studied.The evolutions of the hardness,irradiation defects and microstructure of the heterogeneous interface of V-4Cr-4Ti/Ti after Fe10+implantation at 450℃ or Cu2+implantation at 300-600℃ were studied by nanoindentation and TEM.The results showed that radiation hardening and irradiation defects occurred in all regions during irradiation,and the diffusion interface was lower than the V-4Cr-4Ti and Ti matrix.These results indicated that the interface could play a critical role in the resistance to the generation and proliferation of irradiation defects and radiation hardening.In this paper,the influence of alloy composition on the types of dislocation loops,the 1D motion of dislocation loops,and the evolution of irradiation defects at the heterogeneous interfaces were studied.These studies revealed the interaction of energetic ions and irradiation defects in some metal materials and heterogeneous interfaces,and provides some experimental support for the development of nuclear materials in the future.