纳米压痕形变过程的分子动力学模拟

根据EAM多体势，利用分子动力学方法模拟了Ni压头压入Al基体的纳米压痕全过程．包括压头接近和离开基体时的原子组态；压入和上升时的载荷一位移曲线以及位错的发射和形变带的产生和变化；同时模拟了纳米尺度的应力弛豫行为．结果表明，当压头尚未接触基体时就能吸引基体原子，通过缩颈而互相连接．当压入应力Ts为1．9MPa时，基体Al开始发射位错；当分切应力Td=6．4MPa时，出现形变带．压头上升过程出现反向的拉应力，使基体反向屈服，在卸载过程中基体残留位错的组态不断改变．当压头上升离开基体后能拉着基体通过缩颈而相连，当压头和基体分离后仍粘有基体原子．在纳米尺度也存在应力弛豫现象，其原因是热激活引起的位错发射和运动．

MOLECULAR DYNAMICS SIMULATION OF PLASTIC DEFORMATION DURING NANOINDENTATION

The plastic deformation process during nanoindentation of Ni tip into Al substrate, including loading, unloading and stress relaxation has been studied by using molecular dynamics simulation with EAM potential. Results showed that a connective neck between the indenter and the substrate will be formed when the indenter approaches and leaves the substrate surface. During nanoindentation, the first dislocation is emitted at a critical shear stress TS= 1.9 MPa, and shear bands appear at partial shear stress Td=6.4 MPa. When the indenter moves upwards, a reverse tensile stress appears and results in reverse yield of the substrate and continuous change in dislocation configuration. When the indentation tip is retracted and passed through its initial indentation position, it connects to the substrate by necking, and when the tip broke away from the substrate finally, there still exist some substrate atoms on the tip. Stress relaxation has been observed on the nanoscale, which attributes to heat activated dislocation emission and motion.