Molecular dynamics simulations of a nanobubble's collapse-induced erosion on nickel boundary and porous nickel foam boundary

Nickel (Ni) alloys and their foam composites are extensively acknowledged materials utilized in the construction of propellers and hulls for the shipbuilding industry. Erosion caused by bubble collapse, a well-documented form of damage on ship rudders, propellers and hulls, can alter the physical properties of Ni and its foam, consequently constraining their potential applications. The present study aims to investigate the process of nanobubble collapse and its impact on the mechanical and thermal properties of Ni boundary and porous Ni foam boundary. To achieve this, a molecular dynamics (MD) simulations was used to study nanobubble collapse dynamics near the boundaries. Results indicated that the nanobubble collapses due to the contrasting pressure and velocity at the interface between the shock wave and the nanobubble surface. As the nanobubble collapses, its volume decreases, resulting in the formation of a water nano-hammer with a pressure and temperature of approximately 30 GPa and 5000 K. The high impact of the nano-hammer leads to erosion in the case of the Ni boundary and compression in the porous Ni foam boundary. The mechanical stability of an eroded Ni boundary decreases due to the creation of dislocations under the impact of the nano-hammer. However, the thermal stability of the Ni boundary remains relatively unaffected by the erosion process. The compressed Ni foam boundary exhibits a lower specific surface area, smaller cell size, and shorter struts compared to the uncompressed Ni foam boundary, resulting in increasing of the mechanical and thermal stability.