Direct observation of size scaling and elastic interaction between nano-scale defects in collision cascades

Abstract

Using in-situ transmission electron microscopy, we have directly observed nano-scale defects formed in ultra-high purity tungsten by low-dose high energy self-ion irradiation at 30K. At cryogenic temperature lattice defects have reduced mobility, so these microscope observations offer a window on the initial, primary damage caused by individual collision cascade events. Electron microscope images provide direct evidence for a power-law size distribution of nano-scale defects formed in high-energy cascades, with an upper size limit independent of the incident ion energy, as predicted by Sand et al. [Eur. Phys. Lett., 103:46003, (2013)]. Furthermore, the analysis of pair distribution functions of defects observed in the micrographs shows significant intra-cascade spatial correlations consistent with strong elastic interaction between the defects. PAC 61.72.J-,61.80.Az,68.37.Lp

Irradiation Induced Defect Clustering in Zircaloy-2

“…This also results in the growth of a limited number of clusters, and hence a lower DY and a larger loop size. The similar trends of DY vs. temperature and loop size vs. temperature were also recently found in other materials regardless of their different crystal structures, such as in bcc pure Fe [28][29][30][31] and pure W [32][33][34], and in fcc pure Ni [35] and Ni alloys [36].…”

Energy spectra of primary knock-on atoms under neutron irradiation

“…evolution is currently receiving significant attention, with several groups working on using a combination of experimental observations and atomistic simulations, particularly for W [19,22], to define defect clustering and size-scaling laws. However, while those works are still maturing, here we consider simpler approximations that can make use of the PKA spectra presented in this work.…”

Cascade fragmentation: deviation from power law in primary radiation damage

“…In tungsten (W), which due to its high thermal conductivity and low sputtering yield is the main candidate material for plasma facing components of tokamak fusion devices, including ITER [1], dense collision cascades produce large defect clusters [2]. These are readily visible in an electron microscope [3], making direct comparison between simulation and experiment possible. It has recently been discovered, both by direct molecular dynamics (MD) simulations [4] and transmission electron microscopy (TEM) observations [3], that the distribution of defects as a function of their size is well described by a power law…”

“…These are readily visible in an electron microscope [3], making direct comparison between simulation and experiment possible. It has recently been discovered, both by direct molecular dynamics (MD) simulations [4] and transmission electron microscopy (TEM) observations [3], that the distribution of defects as a function of their size is well described by a power law…”

“…The power law distribution increases the computational demand of microstructural evolution simulations, due to the necessity to include defects of ever increasing size, making it in practice necessary to truncate the distribution [5], which to date has been done in an ad hoc manner. On the other hand, ion irradiation experiments [3] reveal a clear change in the slope of the distribution in the limit of large defect sizes. The reason for the abrupt decline in the frequency of occurrence of defects above a certain critical size has remained an open question.…”