The vacancy defect clusters in polycrystalline pure nickle induced by high-current pulsed electron beam

Abstract

High-current pulsed electron beam (HCPEB) technique is employed to irradiate the samples of polycrystalline pure nickel. The microstructures of the irradiated surface layers are investigated by using transmission electron microscopy (TEM). After HCPEB irradiation, very high value of residual stress is induced in the irradiated surface layer, which leads to the formation of dense dislocation walls and twins. Furthermore, a larger number of vacancy defect clusters including dislocation loops, stacking fault tetrahedra (SFT) and voids are also formed. Among three vacancy defect clusters, the number of SFT is much more than that of two other vacancy defect clusters. The lower dislocation density near the regions with dense SFT is observed and voids are likely to be present in these regions. It suggests that the stress with very high value and strain rate induced by rapid heating and cooling due to HCPEB irradiation could cause the shifting of the whole atomic plane synchronously.