Effects of the phase interface on spallation damage nucleation and evolution in multiphase alloy

The spall behaviors of Cu-34%Zn-3%Pb leaded brass samples with annealing and cryogenic treating conditions were dynamic loaded using one-stage light gas gun experiments under ∼1.515 GPa shock pressure. The effects of α/β phase interface and Pb/matrix phase interface on dynamic damage nucleation, growth, and coalescence in leaded brass specimens were investigated by multidimensional testing techniques. Experiment results showed that voids of incipient spall were mainly nucleated in the interior of the Pb-phases with signs of melting, and a small number of voids were nucleated in α-phase, and both are not nucleated at the interface which contradicts the damage fracture theory under quasi-static loading. Due to the effect of reflection and transmission of shock wave at the phase interface, when the shock wave propagates from α-phase with higher impedance to Pb-phase or β-phase with lower impedance, a tensile pulse will be formed within α-phase. If the tensile pulse has sufficient amplitude voids would be nucleated in α-phase. On the other hand, it is considered that the asymmetry high compression zones in the center of the lead-phase with low impedance were formed by the shock wave convergence effects of matrix/lead quasi-spherical interface, which caused adiabatic temperature rise exceeded melting point of lead due to severe plastic deformation, and finally led to local melting and void nucleation in the center of the lead-phase rather than the tensile stress.