Law and mechanism of impact velocity on spalling and fracture behavior of single crystal nickel

Abstract

In order to reveal the influence of impact velocity (<i>U</i>_p) on the spalling and fracture behavior of single crystal nickel, a non-equilibrium molecular dynamics approach is adopted to investigate the free surface velocity curve, radial distribution function, atomic crystal structures, dislocations, and void evolution process. The results show that the critical impact velocity <i>U</i>_p for spalling behavior in single crystal nickel is 1.5 km/s, and when <i>U</i>_p ≤ 1.5 km/s the spallation mechanism is classical spallation damage and when <i>U</i>_p ＞1.5 km/s it behaves as micro-spallation damage. The pore number and distribution area, and stress distribution area under micro-spallation damage are much higher than those under classical spallation damage. The influence of impact velocity on the classical spalling damage behavior (<i>U</i>_p ≤ 1.5 km/s) is analyzed and the corresponding spalling strength is obtained, indicating that an accident of spalling strength occurs when <i>U</i>_p is 1.3 km/s. The spalling strength of single crystal nickel is influenced by the combined effects of stacking faults, phase transformation, and dislocation. As the nucleation and emission of dislocations increase, the spalling strength decreases. When <i>U</i>_p < 1.3 km/s, the spalling damage is mainly due to stacking faults. When <i>U</i>_p = 1.3 km/s, the spalling strength is mainly affected by the competition between stacking faults and phase transformation. When <i>U</i>_p > 1.3 km/s, spalling strength is predominantly influenced by the body-centered cubic (BCC) phase transformation mechanism (transformation path: FCC → BCT → BCC). This study reveals the impact velocity-dependent patterns, mechanisms, and effects on spalling damage and fracture, providing a theoretical basis for realizing the protective application of nickel-based materials under extreme impact conditions.