聚变材料钨辐照后退火形成的位错环特性及inside-outside衬度分析

Analysis of dislocation characteristics and inside-outside contrasts in irradiated and annealed tungsten as a fusion reactor material

对纯钨透射电镜薄膜样品在400℃进行了58 keV、1×10^(17)cm^(-2)(约0.1 dpa)的氘离子辐照,辐照后进行了900℃/1 h的退火处理.离子辐照产生了平均尺寸为(11.10±5.41)nm,体密度约为2.40×10^(22)m^(-3)的细小位错环组织,未观察到明显的空洞组织.辐照后退火造成了位错环尺寸的长大和体密度的下降,分别为(18.25±16.92)nm和1.19×10^(22)m^(-3).通过透射电镜的衍射衬度分析,判断辐照后退火样品中的位错环主要为a/2<111>类型位错环.通过“一步法”inside-outside衬度分析判断位错环为间隙型位错环.辐照后退火还造成了较大位错环之间接触融合,形成不规则形状的大型位错环.此外,退火后样品中还观察到了尺寸为1—2 nm的细小空洞组织.

Tungsten is an important candidate of plasma-facing material for fusion reactors.Its irradiation response,especially the post-irradiation annealing(PIA)behavior needs further investigating.In addition,the practice of the"inside-outside"contrast method of determining the characteristics of irradiation induced dislocation loops has not been utilized frequently,and the present research serves as an example to present some practical considerations.In the present work,a tungsten thin-foil specimen is irradiated at 400℃with 58 keV D+to a final fluence of 1×10^(17)cm^(-2),corresponding to a dose of about 0.1 dpa.The specimen is prepared through the electro-polishing method by using a NaOH based electrolyte.The ion irradiation is carried out directly on the electro-polished specimen.The irradiated specimen is followed by isothermal annealing at 900℃for 1 h.The as-irradiated and post-irradiation annealing modified defects are investigated with a transmission electron microscope(TEM)operated at 200 kV.The irradiation defects are characterized by using TEM bright-field imaging for the same imaging field with different g vectors around the three major zone axes:the[001],[111],and[Oil]zone axis of the body-center cubic lattice of W.For each g vector,the±g are characterized,and the corresponding contrast-extinctions and"inside-outside"contrasts of selected dislocation loops are identified.The indices of the g vectors around different zone axes are assigned consistently with the Kikuchi map.As a result,the D+irradiation increases a fine distribution of dislocation loops with an average size of(11.10±5.41)nm and a bulk density of 2.40×10^(22)/m^(3).Voids are not observed obviously.The post-irradiation annealing causes the loop size to increase and the loop density to decrease,with numbers of(18.25±16.92)nm and 1.19×10^(22)/m^(3),respectively.Through the contrast-extinction analysis,the dislocation loops in the irradiated and annealed specimen are identified to be a/2<111>-type dislocation loops.The post-irradiation annealing also causes the coalescence of large loops and forms large irregular-shaped dislocation loops.Voids with typical sizes of 1-2 nm are also observed in the annealed specimen.The PIA modified microstructure is consistent with the stageⅣor stageⅤcharacterization of classical PIA induced microstructures.Through the"one-step"inside-outside contrast method,the dislocation loops are identified as an interstitial type.The influcing factors for the"onestep"method are discussed and the importance of consistent indexing is also noted.