纳米尺度摩擦过程的分子动力学模拟

MOLECULAR DYNAMICS SIMULATION OF NANOSCALE FRICTION PROCESS

利用分子动力学方法模拟了刚性金刚石压头在Ni单晶体上的滑动过程,讨沦了压入深度对摩擦力的影响(压入深度对滑动过程中压头下方的微结构演化(能否发射位错环)有很大影响).结合摩擦过程中的塑性行为和能量耗散机制,解释了产生摩擦力锯齿形曲线的原因,证实了位错的形核及湮灭是黏一滑机制的原因之一.不同滑动速度对摩擦力影响的模拟表明,压头的滑动速度决定了压头下方位错环的运动和演化形式:在高速滑动下,形成的位错环依次沿着滑移面很快向Ni单晶基体内扩展;在低速滑动下,压头下方产生的位错环互相发生作用,在材料的亚表面形成较低能量的大位错环,由此产生的塑性变形主要集中在材料的亚表面.

The nano-scratch process of a rigid diamond tip into Ni single crystal has been studied by using molecular dynamics simulation with EAM potential. The effects of scratch depth on the friction force, microstructures around the tip and formation of dislocation loops in the scratch process were analyzed. It is revealed that the stick-slip phenomenon is resulting from dislocation emission and phonon dissipation. The sawtooth phenomena can be explained as that elastic energy stored in the stick process transforms to the dislocations beneath the tip, and then dissipates in the form of phonons, and finally forms the surface defects. Finally, simulation also shows that the scratch velocity is the critical factor on the dislocation loop nucleation and evolution process. At the higher velocity, dislocation loops glide along slip plane downward to the bulk material. At the lower velocity, dislocation loops beneath the tip will react with each other to form a large loop under the subsurface of the material, and plastic deformation will concentrate on the subsurface of the material.