Orientation sensitivity of focused ion beam damage in pure zirconium: direct experimental observations and molecular dynamics simulations

Abstract

A high-purity predominantly single crystalline zirconium was subjected to controlled focused ion beam (FIB) damage. Damage estimates were obtained from electron backscattered diffraction (EBSD) and nano-indentation measurements on exactly the same area/orientation. The damage kinetics, between different crystallographic orientations, differed by one order of magnitude and a clear hierarchy of orientation sensitive ion damage emerged. Use of a simple geometric approach, linear density of atoms and corresponding scattering cross-sections to impinging gallium ions, could differentiate between extreme damage kinetics; but failed when such differences were relatively minor. Numerically intensive molecular dynamics (MD) simulations, on the other hand, were more effective. However, MD simulations or direct EBSD observations failed to justify anisotropic irradiation hardening (AIH): 3-8 times more hardening for near basal. Though explanation for AIH is indirect, evidence and rationalization for orientation-sensitive radiation damage appears clear and statistically reproducible.

Grain boundary energy and relative ion damage: experimental observation and molecular dynamics simulation

“…Molecular dynamics (MD) simulations captured the overall trends in experimental ion damage. The present study is an extension of this earlier [6] study. This manuscript is aimed at extracting damage kinetics, experimental and simulated, for grain boundaries in Zr bi-crystals.…”

“…The damage may initiate a range of structural changes [1][2][3]. Such changes are anisotropic [3][4][5][6], as they typically depend on the microstructural features present. For example, grain or crystal orientations are expected [4][5][6] to affect damage kinetics.…”

“…Such changes are anisotropic [3][4][5][6], as they typically depend on the microstructural features present. For example, grain or crystal orientations are expected [4][5][6] to affect damage kinetics. A recent study [6] had used a combination of focused ion beam (FIB) damage and high-resolution electron backscattered diffraction (EBSD): to bring out aspects of orientation sensitive ion damage in predominant single-crystalline 6N (99.9999 wt%) purity Zr (Zirconium).…”

“…For example, grain or crystal orientations are expected [4][5][6] to affect damage kinetics. A recent study [6] had used a combination of focused ion beam (FIB) damage and high-resolution electron backscattered diffraction (EBSD): to bring out aspects of orientation sensitive ion damage in predominant single-crystalline 6N (99.9999 wt%) purity Zr (Zirconium). Molecular dynamics (MD) simulations captured the overall trends in experimental ion damage.…”

“…Near boundary region of this material was thus considered as effective bi-crystals. Electropolished [6] samples were subjected to vacuum annealing: 400°C, 6 h annealing under 10 −8 torr. This enabled formation of thermal grooves without any oxidation.…”