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In this work, molecular dynamics simulations are employed to study the nanotribological process of nickel-based polycrystalline superalloy coating. A series of simulations were carried out using the method of repeated friction to explore the influence of frictional force, friction coefficient, grinding groove morphology, wear scar depth, debris flow direction, subsurface damage degree and evolution of defects during the nano-friction process. In addition, the change mechanism of different grain sizes on wear scar depth, frictional force, friction coefficient, and internal damage in the repeated friction process is also explored. The results show that the frictional force is related to the direction of the dislocation slip, and that the friction coefficient change is related to the number of repeated frictions. Moreover, it is observed that the grinding ball has a shunting effect on the formed wear debris atoms, and the shunt point is located at the maximum horizontal radius. We reveal that the grain boundary structure has a strengthening effect. When the grinding ball rubs to the grain boundary, the nucleation of dislocation defects inside the workpiece is obviously hindered by it. Simultaneously, we also find that the closer the subsurface is to the bottom of the grinding ball, the greater the degree of damage to the workpiece by friction. Furthermore, with the grain size decreases that the material begins to soften, resulting in a decrease of frictional force, friction coefficient, and smaller defects are formed inside the workpiece. The research of this work can better clarify the microscopic mechanism of the polycrystalline friction process.

The solidification microstructure of Mg-6Zn-3Y alloy under super-high pressure was investigated by using X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the dendritic structure of Mg-6Zn-3Y alloy under super-high pressure (GPa level) can be evidently refined with the increase of solidification pressure. When the pressure increases to 2 GPa, Y element can’t solubilize in matrix of a-Mg, the primary Y solid solution is distributed in the shape of polygon block in the matrix. When the pressure is up to 4 GPa, the primary Y solid solution appears as symmetrical petaline shape. So Y solid solution exhibits the different morphology with the change of the pressure