Microstructure evolution and reaction behavior of Cu-Ni alloy and B4C power system was studied by in-situ and static experimental investigations along with theoretical calculations.The reaction process was as follows.Firstly,B4C decomposed into B and C atoms,and then B atoms diffused into Cu-Ni matrix,leading to the formation of Ni2B particles.Subsequently,Ni atoms diffused into B4C,forming a loose mixture of Ni2B and amorphous C at the initial powder boundary.Finally,with the completion of reaction,Ni2B particles at the powder boundary grew into a monolithic block,and then C substance was excluded out and accumulated at the edge of this monolithic Ni2B block.It is believed that the formation of Ni2B phase is caused by the most negative change of Gibbs free energy among all the potential reactions between Ni-B and Ni-B4C systems.