单晶锗纳米尺度分层多次切削的分子动力学模拟

Molecular Dynamics Simulation on Nano-scale Layered Multiple Cutting of Monocrystalline Germanium

运用分子动力学方法研究了单晶锗材料在多次切削过程中晶体结构的演化和相变。比较了在相同的总加工深度下采用两次不同预设切削深度加工单晶锗后表面/亚表面损伤程度、温度和应力的变化。研究结果表明:切削过程中切削区原子发生高压相变,原子结构从Ge-Ⅰ结构转变为无定形结构,使工件发生塑性变形,切屑以塑性方式去除;切削结束后由于压力和温度释放,少量无定形结构原子重新转变为Ge-Ⅰ结构或六方金刚石结构,而无定形结构主要是β-tin结构和非晶体结构;预设切削深度增加,材料的去除量和亚表面损伤深度增加,其损伤深度不受前一次切削深度影响,仅与最终预设切削深度相关,并且在同样条件下,多次切削比单次切削更有利于降低亚表面损伤深度和提升加工效率。此外,原子相变与σ_(xx)和σH_(yd)相关,亚表面损伤深度与σ_(yy)相关,两次预设切削深度接近或相等时,工件内部应力均衡有利于形成较好的加工表面。

Crystal structure evolution and phase transition of monocrystalline germanium during multiple cutting were studied by molecular dynamics method.The changes in surface/subsurface damage,temperature and stress after processing of monocrystalline germanium at two different preset cutting depths were compared for the same total machining depth.The results show that:during the cutting process,the atoms in the cutting zone undergo high-pressure phase transformation,and the atomic structure changes from Ge-Ⅰ structure to distorted structure,so that the workpiece is plastically deformed and the chip is plastically removed.After the cutting process,due to pressure and temperature release,a small amount of distorted structure atoms are reconverted into Ge-Ⅰ structure or hexagonal diamond structure,and the distorted structure is mainly β-tin structure and amorphous structure.With increasing preset cutting depth,the amount of material removal and subsurface damage depth increase,and subsurface damage depth is not affected by the previous cutting depth but related to the final preset cutting depth.Under the same conditions,multiple cutting is more conducive to reducing subsurface damage depth and improving processing efficiency than single cutting;In addition,atomic phase transformation is related to σ_(xx) and σH_(yd),and subsurface damage depth is related to σ_(yy).When the two preset cutting depths are close or equal,the internal stress balance of the workpiece is favorable for forming a better machined surface.