Rapid elimination of high-thermal-stability Ni-Mn-Si nanoclusters causing hardening in reactor pressure vessel steel using pulsed electric current treatment

Under long-term conditions of high temperature, high pressure, and high neutron flux, reactor pressure vessel steel forms post-burst-phase Ni-Mn-Si clusters, which seriously deteriorate its mechanical properties. Eliminating Ni-Mn-Si clusters generated during service is crucial to ensuring the reliable operation of the reactor pressure vessel, which cannot be replaced. This study exploits the difference in electrical resistance between the clusters and the matrix by introducing additional free energy via a pulsed electric current to dissolve irradiation-induced Ni-Mn-Si clusters. The nanohardness of irradiated reactor pressure vessel steel increased by 2.13 GPa, and the hardness fully recovered after pulse treatment. Similarly, the number density of clusters decreased by more than 90%, and the volume fraction decreased by more than 95% after treatment. The study also found that high-frequency pulsed current is much more effective than low-frequency pulsed current in simultaneously eliminating clusters. Compared with traditional annealing treatments, this method features a shorter processing time (only 30 minutes), higher hardness recovery efficiency (over 90%), and a lower processing temperature. By applying a pulsed current to rearrange the internal elements of the matrix and enhance its mechanical properties, this method provides a new solution for the repair and life extension of nuclear power materials.