New perspectives on collision cascade damage in self-ion irradiated tungsten from HR-EBSD and ECCI

JOURNAL OF NUCLEAR MATERIALS

卷:554

Article

Yu, Hongbing¹  Karamched, Phani²  Das, Suchandrima¹  Liu, Junliang²  Mizohata, Kenichiro³  Hofmann, Felix¹ 

[1] Univ Oxford, Dept Engn Sci, Parks Rd, Oxford OX1 3PJ, England

[2] Univ Oxford, Dept Mat, Parks Rd, Oxford OX1 3PH, England

[3] Univ Helsinki, POB 64, Helsinki 00560, Finland

关键词: Irradiation damage;    Strain;    Tungsten;    Long-range ordering;    Dislocation loops;   

DOI  :  10.1016/j.jnucmat.2021.153074

来源: Elsevier

【 摘 要 】

Understanding defect production and evolution under irradiation is a long-standing multi-scale problem. Conventionally, experimental examination of irradiation-induced dislocation loops (IIDLs) has mainly relied on transmission electron microscopy (TEM), which offers high spatial resolution but only limited strain sensitivity (strains less than 0.1% are challenging to evaluate). TEM also requires very thin samples, making multi-scale characterisation and quantitative strain measurements difficult. Here, we explore the potential of using advanced techniques in the scanning electron microscope (SEM) to probe irradiation damage at the surface of bulk materials. Electron channelling contrast imaging (ECCI) is used to image nano-scale irradiation-induced defects in 20 MeV self-ion irradiated tungsten, the main candidate material for fusion reactor armour. The results show an evolution of the damage microstructure from uniformly and randomly distributed nano-scale defects at 0.01 dpa (displacement per atom) to raft structures extending over hundreds of nanometres at 1 dpa. Cross-correlation based high-resolution EBSD (HR-EBSD) is used to probe the lattice strain fields associated with IIDLs. While there is little strain fluctuation at 0.01 dpa, significant heterogeneity in the lattice strains is observed at 0.1 dpa, increasing with dose until saturation at 0.32 dpa. The characteristic length scale of strain fluctuations is similar to 500 nm. Together, ECCI and HR-EBSD reveal a transition from a structure where defects are disordered to a structure with long-range order driven by elastic interactions between pre-existing defects and new cascade damage. (C) 2021 Elsevier B.V. All rights reserved.

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