Mechanical behaviour near grain boundaries of He-implanted UO2 ceramic polycrystals

Abstract For studying the micromechanical behaviour of UO 2 and characterising the intergranular interaction, polycrystals are implanted with helium ions, inducing strains in a thin surface layer. Laue X-ray micro-diffraction is used to measure the strain field in this implanted layer with a spatial resolution of about 1 μm. It allows a 2D mapping of the strain field in a dozen of grains. These measurements show that the induced strain depends mainly on the crystal orientation, and can be evaluated by a semi-analytical mechanical model. A mechanical interaction of the neighbouring grains has also been evidenced near the grain boundaries, which has been well reproduced by a finite element model. This interaction is shown to increase with the implantation energy ( i.e. the implantation depth): it can be neglected at low implantation energy (60 keV), but not at higher energy (500 keV).