Twin boundary spacing-dependent friction in nanotwinned copper

Abstract

The deformation mechanisms of nanotwinned Cu subjected to nanoscratching are investigated by means of molecular dynamics simulations. Scratching simulations on nanotwinned single-crystalline Cu with the twin planes parallel and perpendicular to the scratching direction are performed. Since the detwinning mechanism is completely suppressed in the former case, no apparent correlation between frictional coefficient and the twin spacing is observed. In samples where the twin planes are perpendicular to the scratching direction, the friction increases as the twin spacing decreases, and then decreases as the twin spacings become even smaller. It results from the competitive plastic deformation between the inclined dislocations and the detwinning mechanism. Subsequent simulations for nanotwinned polycrystalline Cu unveil that in addition to the grainboundary-associated deformation mechanism, dislocation-mediated detwinning plays a significant role in the plastic deformation of nanotwinned Cu. The twin boundary spacing in turn affects nanotwinned materials to resist scratching via plastic deformation. We demonstrate via the nanoscratching tests that there exists a critical twin boundary spacing for which the friction coefficient is maximized and that this transition results from the competing deformation mechanisms in those nanotwinned materials.

Mechanisms of anisotropic friction in nanotwinned Cu revealed by atomistic simulations

“…Previous experimental investigations and atomistic simulations have demonstrated that the plastic deformation of polycrystalline NT Cu under friction is governed by several individual deformation mechanisms working in parallel, such as dislocation slip, TB migration, detwinning, deformation twinning and GB-associated mechanism [21][22][23][24]. This work further indicates that the competition between individual deformation mechanisms strongly depends on internal microstructures and loading conditions, i.e.…”

Breakdown of Shape Memory Effect in Bent Cu–Al–Ni Nanopillars: When Twin Boundaries Become Stacking Faults

“…The transition, with decreasing sample size, from twinning to stacking faults may also be reflected by another approach based on the nucleation process of twins and stacking faults. It has been argued that twinning progresses via partial dislocations and the plane-to-plane propagation of partial dislocation slips. − It was then shown that these two steps have opposite size dependence, − namely small sample sizes increase the probability of first partial dislocations while decreasing the probability of plane-to-plane propagation of partial dislocation slips. On average, it seems that smaller sample sizes will suppress twinning in this model.…”

“…Investigations of size dependent mechanical twinning under compression have already revealed some grain-size dependence. − The grain size effect of twinning has been reported in nanocrystalline Ni and Cu , and has been attributed to the competition between the grain size-dependence of partial dislocations and the layer-by-layer promotion of partial slip near the surface. Hexagonal close-packed Ti–5%Al (atom %) crystal pillars show that the stress required for deformation twinning increases drastically for compression and samples sizes (∼1 μm), below which twins are suppressed and replaced by dislocations .…”

Subsurface damage mechanism of high speed grinding process in single crystal silicon revealed by atomistic simulations

“…3(b) that variations of SSD thickness for different grinding speeds are at grinding distance 14 nm. Measurement of SSD thickness is based on variations of the potential energy of atoms in different regions with different deformation behaviors [49], and diamond structure atoms excluded for a clearer visualization of the defect structures [50]. Fig.…”