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.

Keywords:

• ion damage
• zirconium
• microstructure
• microtexture
• orientation
• EBSD
• FIB
• molecular dynamics
• irradiation hardening

Acknowledgements

The authors would like to acknowledge support from DST (Department of Science and Technology, India) for establishing the National Facility of Texture and OIM (Orientation Imaging Microscopy) at IIT Bombay. Financial Support from BRNS (Board of Research on Nuclear Sciences, India) is gratefully acknowledged.

Notes

1. Other indices, as in Figure 2, yielded similar results.

2. This order is based on CI: KAM estimates did not provide a distinction between intermediate and lowest.

3. When θ equals 0°, the direction is parallel to the plane normal (normal to plane of impingement) and when θ equals 90°, the direction lies in the plane of impingement.