Oxygen diffusion saturation of hafnium with the different surface layer

Abstract

Hafnium is used for the production of control rods and protective screens in nuclear reactors after its hot plastic deformation and final thermochemical treatment. This research presents the experimental results of the influence of the surface layer state on the oxygen diffusion saturation of hafnium during thermochemical treatment in an oxygen-containing gas medium. Two cases of the surface layer state were considered: in the initial (delivery) state and after grinding, where 50 μm of the surface layer was removed. Differences between the hardness distributions in the near-surface layer of HFE-1 hafnium after thermochemical treatment in an oxygen-containing gas medium were shown. It was found that thermochemical treatment of hafnium with a surface layer in its initial state leads to an increase of hardness in the near-surface layer compared to the surface: i.e., the near-surface layer hardness increases to a depth of 5 - 7 μm, and then gradually decreases to the matrix (core) hardness. It was determined that the fatigue life of hafnium after thermochemical treatment depends on the surface layer state. A 6.5 times higher fatigue life after thermochemical treatment of hafnium samples was fixed with a grinded surface compared to hafnium samples without grinding.