Molecular dynamics study of shock-induced deformation phenomena and spallation failure in Ni-based single crystal superalloys

Abstract

Shock-induced dynamic mechanical behavior and spallation failure of Ni-based single crystal superalloys are studied via non-equilibrium molecular dynamic simulations. The results show that the spallation failure of Ni-based single crystal superalloys exhibits two modes of classical spallation and micro-spallation. At low shock velocity, the deformation mechanism is dominated by slip and drag of dislocations. As the shock velocity increases, the atomic structure undergoes complex phase transitions from FCC to BCC or disordered structures, and the spallation strength gradually decreases. The decreasing tendency of the spallation strength corresponds to the characteristics of the deformation process. Moreover, the spallation strength and spallation threshold velocity drop significantly with increasing initial temperature, which is due to the softening of Ni-based single crystal superalloys at high temperatures. In addition, the plastic mechanism dominated by shear stress leads to void collapse along the vertical direction at lower shock velocities, while the internal jetting mechanism, controlled by normal stress, induces void collapse in the horizontal direction under higher shock velocities. The existence of voids significantly lowers the spallation strength, and the amplitude reduction of the strength is directly proportional to the radius of the voids.