Effect of radiation defects on grain boundary evolution under shock loading

Abstract

Grain boundary (GB) failure in tungsten under shock loading after irradiation is a key factor to estimate the performance of tungsten as a plasma facing material in nuclear fusion reactors and as a target in spallation neutron sources. In this work, GB evolution after absorption of different radiation defect clusters under shock loading has been investigated at atomic scale through non-equilibrium molecular dynamics (NEMD) method. Different to the cases without radiation defects, after absorption of interstitial dislocation loops and voids, two mechanisms have been identified for the decrease of critical shock velocity (vc) and the related GB failure. The direct void growth accompanied by appearance of disordered structure around void, from the remaining vacancy cluster which could not be annihilated by compressive stress wave, is the 1st mechanism. In the 2nd mechanism, activation of slip systems, dislocation formation, motion and multiplication, void nucleation and growth dominate the failure process. The higher potential energy and local stress concentration around a defect absorption region in GB are recognized for atomic motion deviations from shock loading direction, resulting in formation of disordered structure, activation of slip system and dislocation multiplication with lower vc under coupling effects of radiation damage and shock loading. These results indicate that under a high dose of radiation damage, GB failure induced by shock loading should be considered seriously in order to estimate the lifetime of tungsten-based plasma facing materials and spallation target materials.

Keywords

• Shock loading
• Grain boundary failure
• Radiation damage
• Void nucleation
• Slip system activation