Impurity segregation at grain boundaries(GB)is one of the significant effects on the mechanical properties of alloys,e.g.,embrittlement and cracking.Experiments on the Reactor Pressure Vessel(RPV)steel and Fe-Cu alloys indicate that Cu-rich clusters produced by irradiation play an important role in the hardening and embrittlement of materials[1].The very low solubility of Cu atoms in bcc Fe may also trigger Impurity segregation at grain boundaries (GB) is one of the significant effects on the mechanical properties of alloys, eg, embrittlement and cracking. Experiments on the Reactor Pressure Vessel (RPV) steel and Fe-Cu alloys that that Cu-rich clusters produced by irradiation play an important role in the hardening and embrittlement of materials [1]. The very low solubility of Cu atoms in bcc Fe may also trigger