Effect of the sonic shock wave on void evolution in materials under irradiation

Abstract

Understanding the void-cascade interaction is of great importance for clarifying the irradiation damage as a major challenge in nuclear industry, since it typically causes void annihilation or shrinkage, which greatly affects the swelling of irradiated materials. But the current understanding of it is extremely limited due to the neglect of the sonic shock wave. Herein, we take γ-U as the representative model due to the emergence of a violent sonic shock wave there. Molecular dynamics simulations are performed to explore the underlying mechanism of the sonic shock wave interacting with voids. It is firstly revealed that the sonic shock wave is essentially focusons along <111> crystal orientation family, attributed to the highest energy transfer efficiency along <111> in γ-U. These focusons can cause void annihilation or shrinkage via sliding, while thermal spikes only cause annihilation by covering voids. Combining these two factors, we propose a model to qualitatively epitomize the void-cascade interaction, in which the influence scope exhibits an intriguing anisotropic feature, overturning a long-accepted view that the void-cascade interaction is isotropic. This model is further generalized to other nuclear materials owing to the similar mechanism of the sonic shock wave. Moreover, we find distinct size effect of voids on void-cascade interaction. Thermal spikes hardly affect voids that are too large to be covered, while the sonic shock wave also causes visible shrinkage in large voids. The present work proves that the sonic shock wave has a non-negligible effect on void evolution, improving the fundamental understanding of void-cascade interaction in irradiated materials.