High Resolution Electron-Microscope Study of Damage Evolution Processes in Metals and Their Alloys Irradiated with High Energy Particles

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In the present work, we developed the cryotransfer technique of electron microscopy of ion- and neutron-irradiated at low temperature. From the experimental results of cryotransfer TEM of ion-, fission-neutron- and fusion-neutron-irradiated metals at low temperature, the following processes are decleared for the formation and evolution of damage cascades in high energy particle-irradiated metals. (1) When the primary snock-on atom is generated in metals, it stops after the collision with other lattice atoms and forms the displacement damage cascade whose the central part is occupied by high concentration of vacancies and is surrounded by the interstitial mantle. Previously it was believed that vacancies agglomerate to form TEM visible clusters (i. e. cascade collapse) and interstitials escapes to nearby sinks. In the present work, it was found that vacancies form sub-electron microscope size of clusters which are invisible by TEM while interstitials form TEM visible clusters. (2) It wa … More s clarified that sub-EM sizes of clusters of both vacancy and interstitial type were formed together with visible defects. (3) With increasing the fluence, TEM-invisible clusters tend to change to TEM visible clusters. This occurs due to the assistance of lattice relaxation by emitted energies from new cascades formed nearby previously formed ones. This effect is named by the present scientists "cascade energy overlapping". We believe that this effect is due to the shock-wave emitted at new formed cascade. The details of mechanism is at present studying by molecular-dynamical simulation with super-computer.(4) Interstitial atoms are emitted intensely towards the outside of cascade core and form TEM visible clusters. The distance was found to be fairly larger when it was compared with that due to the replacement collision sequence. We are proposing that an interstitial atom is transported by surfriding mechanism on the shock wave generated. This may be a reason why many interstitial dot defects form at concentrated place (i. e. groupings). These point defect processes of the formation of damages in metals which are irradiated at high temperature was examined extensively especially for the damage structure evolution and void formation. Less