Dislocation interactions with twin boundary (TB) have been well-established in nanotwinned metals. Penta-twins, as an extreme of crystal twinning, are tacitly assumed to be more effective at blocking dislocation motions than conventional single or coplanar nanotwins. However, the mechanism underlying between dislocations and penta-twins remains largely unclear. Here, by combining situ transmiss...

This paper discusses three aspects that have not been looked into within mechanistic model for rationalizing observed behavior of nanocrystalline materials. (1) For the nano-materials with low energy barrier to emit the trailing partial after the leading partial, such as nanocrystalline Al (nc-Al), both partials extend intra-granularly in strengthening effect. (2) In the transition grain-size r...

Highly oriented [111] Cu grains with densely packed nanotwins have been fabricated by direct-current electroplating with a high stirring rate. The [111]-oriented and nanotwinned Cu (nt-Cu) allow for the unidirectional growth of Cu(6)Sn(5) intermetallics in the microbumps of three-dimensional integrated-circuit packaging; a uniform microstructure in a large number of microbumps of controlled ori...

The strength and ductility of nanolayered materials are determined by a delicate balance between dislocation and interface motion under applied mechanical loading. We present here studies of dislocation and interface motion in single crystal and nanotwinned copper, utilizing molecular dynamics simulations. Motion of twin boundary interfaces themselves is dictated by the stress state at the inte...

Twin boundaries have been exploited to stabilize ultrafine grains and improve the mechanical properties of nanomaterials. The production twin nanotwins is however prohibitively challenging in carbide ceramics. Using scanning transmission electron microscopes as a unique platform for atomic-scale structure engineering, we demonstrate that platelets could be produced carbides by engineering antis...

accumulative roll-bonding (arb) is a severe plastic deformation process that is using rolling to produce ultrafine grains in coarse grained metallic materials. in this study, arb has been applied on 70/30 brass up to 6 cycles at ambient temperature and non-lubricated conditions to apply a true strain up to 4.8 von mises strain. microstructures of arbed brass samples were characterized by scanni...

Atomistic simulations are performed to study the structure and geometrical limit of nanoscale twins in NiTi shape memory alloys. We analyze compound twins as narrow as 1 nm, involving a few atomic layers. A novel nanotwinned structure is found, forming through the martensitic transformation of sublattices. We predict the temperatures of phase transformation, which are consistent with experiment...