Effect of Gallium ion damage on poly-crystalline Zirconium: Direct experimental observations and molecular dynamics simulations

This study involved controlled focused ion beam (FIB) damage of high purity poly-crystalline Zirconium (Zr) and EBSD (electron backscattered diffraction) observations on the same region/microstructure. Direct experimental observations were augmented by molecular dynamics (MD) simulations: the latter demonstrating a hierarchy of microstructural features enabling/retarding relative ion damage. Experimental results clearly established a non-monotonic dependence of damage kinetics with average grain size. Damage increased with grain size, till an average grain size of 12 micron, and then dropped. This was explained from combined effects of grain size and in-grain misorientations. For lower than 12 micron average grain size, noticeable in-grain misorientations enabled lower damage kinetics. For greater than 17 micron grain size, with insignificant in-grain misorientations, reduced presence of high angle grain boundaries were shown to retard relative ion damage.