Dislocation cores are represented by thin tubes, in which Shockley partial dislocation with 1/6 <112 > Burgers vector and perfect dislocation with 1/2 <110 > Burgers vector are colored gray and red, respectively. It is seen from Figure 4b that the dislocation loop consists of four

partial dislocations and one perfect dislocation. In addition, there is one vacancy formed beneath the probe. Upon further penetration, the other selleck kinase inhibitor three 111 slip planes are activated sequentially, and Figure 4c shows that the defect zone beneath the probe expands greatly. The glide of dislocations on adjacent slip planes leads to the formation of stair-rod dislocations with 1/6 <110 > Burgers vector highlighted by the arrows in Figure 4d. Figure 4e,f presents dislocation network after the completion of scratching and penetration, respectively. It is seen from Figure 4e that there is less dislocations but more

vacancies in the wake of the probe than that in the vicinity of the probe due to the plastic recovery. In addition to the stair-rod dislocations, there are glissile prismatic dislocation loops formed by dislocation reaction and cross-slip events. In particular, the prismatic dislocation half-loops in front of the probe glide parallels to the free surface to transport the materials displaced by the probe without the formation of surface steps [24]. Although small part of the dislocations beneath the probe annihilates at the free surface during the retraction,

Figure 4f shows that the defect structures are stable. Figure AZD2014 4 Close inspections of defect structures in friction with a probe radius of 8 nm. The scratching depth is 0.82 nm. (a,c) Bottom views of defect structures at penetration depths of 0.72 and 0.82 nm, respectively. Atoms are colored according to their BAD values and FCC atoms are not shown. (b,d) Dislocation networks shown in (a) and (c), respectively. (e,f) Dislocation networks after the completion of scratching and retraction, respectively. Effect of probe radius on minimum wear depth To investigate the influence of probe radius on the minimum wear depth, friction simulations CYTH4 with another three probe radiuses of 6, 10, and 12 nm are conducted, in addition to the probe radius of 8 nm. For each probe radius, the penetration stage stops at a penetration depth that is 0.1 nm deeper than the critical penetration depth at which the phenomenon of force drop occurs. Figure 5a,b plots the contact pressure-penetration depth curves and the friction coefficient-scratching length curves during the penetration and scratching stages with the four probe radiuses, respectively. The contact pressure is defined as the ratio of the penetration force to the contact area. A detailed description about the calculation of the contact area during spherical penetration can be found elsewhere [28].