Molecular Dynamics Investigation of Residual Stress and Surface Roughness of Cerium under Diamond Cutting

Effects of crystallinity on residual stresses via molecular dynamics simulations

Mechanical properties of materials are highly dependent on microstructure. One characteristic example is tensile stresses at the grain boundaries, which is one of the most critical factors in crack nucleation. Although experimental techniques have significantly evolved during the past decades with respect to obtaining high-resolution snapshots of the microstructure with methods such as scanning electron microscopy, the quantitative estimation of continuum quantities, such as localized stresses, still remains a very challenging task. The molecular dynamics simulation method has been proven to be a quite effective simulation tool for providing insights in such challenges due to its high spatial and temporal resolution. In this study, molecular dynamics simulations have been performed to obtain a spatial resolution of the residual stresses in solidified aluminum. A best-effort realistic microstructure was obtained by starting from a pure aluminum block which was initially melted and subsequently quenched under various cooling rates, and finally relaxed. The obtained results suggest that residual stresses are higher in absolute terms at the vicinity of grain boundaries than at the grain interiors, and higher crystallinity has been found to be correlated to lower residual stresses. Moreover, it has been shown both qualitatively and quantitatively that grain boundaries undergo tensile loading, in contrast to the grain interiors which are compressed; this result comes to support the conclusions of quite recent experimental investigations, showing that the residual stress is tensile at the grain boundaries and gradually transits into compressive in the grain interiors, and highlights the potential of molecular dynamics simulation to capture nanoscale physical phenomena.

Effects of Anisotropy on Single Crystal Silicon in Polishing Non-Continuous Surface

A molecular dynamics model of the diamond abrasive polishing the single crystal silicon is established. Crystal surfaces of the single crystal silicon in the Y-direction are (010), (011), and (111) surfaces, respectively. The effects of crystallographic orientations on polishing the non-continuous single crystal silicon surfaces are discussed from the aspects of surface morphology, displacement, polishing force, and phase transformation. The simulation results show that the Si(010) surface accumulates chips more easily than Si(011) and Si(111) surfaces. Si(010) and Si(011) workpieces are deformed in the entire pore walls on the entry areas of pores, while the Si(111) workpiece is a local large deformation on entry areas of the pores. Comparing the recovery value of the displacement in different workpieces, it can be seen that the elastic deformation of the A side in the Si(011) workpiece is larger than that of the A side in other workpieces. Pores cause the tangential force and normal force to fluctuate. The fluctuation range of the tangential force is small, and the fluctuation range of the normal force is large. Crystallographic orientations mainly affect the position where the tangential force reaches the maximum and minimum values and the magnitude of the decrease in the tangential force near the pores. The position of the normal force reaching the maximum and minimum values near the pores is basically the same, and different crystallographic orientations have no obvious effect on the drop of the normal force, except for a slight fluctuation in the value. The high-pressure phase transformation is the main way to change the crystal structure. The Si(111) surface is the cleavage surface of single crystal silicon, and the total number of main phase transformation atoms on the Si(111) surface is the largest among the three types of workpieces. In addition, the phase transformation in Si(010) and Si(011) workpieces extends to the bottom of pores, and the Si(111) workpiece does not extend to the bottom of pores.