| Abstract: | The nano scratch process of a rigid diamond tip into Ni substrate has been studied by using molecular dynamcs simulation with EAM potential. Simulations are carried out to investigate the scratch depth effect on the friction force in the scrath process. Furthermore, microstructures around the tip are strongly depended on the scratch depth and dislocation loops can be formed with enough penetration depth. Also, present study reveals that stick-slip phenomenon results from dislocation emission and phonon dissipation. The sawtooth phenomena can be explained from the point 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, effect of the sliding velocity is studied, which can be deduced from the simulation. The scratch velocity is the critical factor on the dislocation loop nucleation and evolution process. At the higher velocity, dislocation loop glide along slip lane downward to the bulk material. While at the lower velocity, dislocation loops beneath the tip will reaction with each other, and finnaly a large loop will be formed under the subsurface of the material. Plastic deformation will focus on the subsurface of the bulk material under low scratch velocity. |
