Evolution of radiation-induced lattice defects in 20/25 Nb-stabilised austenitic stainless steel during in-situ proton irradiation

We have monitored in situ the lattice defect evolution induced by proton irradiation in 20Cr-25Ni Nb-stabilised stainless steel, used as fuel cladding material in advanced gas-cooled reactors. At 420 degrees C, the damaged microstructure is mainly characterised by black spots and faulted a(0)/3 < 111 > Frank loops. Defect saturation is reached at only 0.1dpa. In contrast, at 460 degrees C and 500 degrees C proton bombardment induces the formation of a mixture of a(0)/3 < 111 > Frank loops and perfect a(0)/2 < 110 > loops. These perfect loops evolve into dislocation lines that form a dense network. This transition coincides with the saturation in the dislocation loop size and number density at 0.8dpa (460 degrees C) and 0.2dpa (500 degrees C), respectively. The presence of a high density of dislocation loops and lines at those two temperatures causes a vacancy supersaturation in the matrix, leading to the formation of voids and stacking fault tetrahedra. (C) 2018 Elsevier B.V. All rights reserved.