纳米Ni薄膜在摩擦过程中塑性行为的分子动力学模拟

用分子动力学模拟研究了金刚石压头在Ni晶体薄膜上的摩擦过程和薄膜塑性变形行为的纳观机制.结果表明:在摩擦过程中,穿晶层错和棱形位错环是纳米薄膜结构传递塑性变形的两种载体,纳米薄膜晶界捕获位错阻滞了塑性变形向薄膜晶界下方材料中传播.摩擦过程中易在较薄的薄膜表面和薄膜晶界之间产生穿晶层错,穿晶层错的产生增加了薄膜蓄积塑性变形的能力,从而抑制材料表面摩擦力在黏滑过程中的振荡幅度;在比较厚的薄膜中不易生成穿晶层错,在摩擦过程中位错环依次向体材料发射,并与晶界反应,湮灭于晶界,黏滑动摩擦响应与单晶相似.由于不同厚度薄膜塑性变形产生的位错结构不同,使得在摩擦过程中亚表面微结构的演化亦不同.

MOLECULAR DYNAMICS SIMULATION OF PLASTIC BEHAVIOR OF THE Ni NANOFILM DURING SCRATCH PROCESS

The nanoscrath process of nickel nanofilm and plastic deformation mechanisms in the nanofilm are investigated by using molecular dynamics simulation. The results reveal that the stacking faults end at the grain boundaries as well as prismatic dislocation loops, leading to that plastic deformation on the grain boundary keeps in the film rather than transmiting downward the substrate. For thinner films, stacking faults are preferred in the scratch process, which increase storage capacity of plastic deformation in the film, and further inhibit the stick–slip amplitude in the friction oscillation process. For thicker films, dislocation loops, which glide along slip plane downward to the grain boundary, dominate over the stacking faults, and finally dissipate on the grain boundaries. Since the intergrain stacking faults are inactive in thicker films, the stick–slip phenomenon is similar to that in single crystal. The evolutions of subsurface microstructures in the nanoscratch process result from the dislocation structures emitted in nanofilms with different thickness.