Nanocrystalline nc materials are known to deform via mechanisms not accessible to their coarse-grained counterparts. For example, deformation twins and partial dislocations emitted from grain boundaries have been observed in nc Al and Cu synthesized by severe plastic deformation SPD . This paper further develops an earlier dislocation-based model on the nucleation of deformation twins in nc fac...

We discuss how simulations of mechanical properties of materials require descriptions at many different length scales — from the nanoscale where an atomic description is appropriate, through a mesoscale where dislocation based descriptions may be useful, to macroscopic length scales. In some materials, such as nanocrystalline metals, the range of length scales is compressed and a polycrystallin...

The effects of crystal-plasticity on the U-Th-Pb system in zircon is studied by quantitative microstructural and microchemical analysis of a large zircon grain collected from pyroxenite of the Lewisian Complex, Scotland. Electron backscatter diffraction (EBSD) mapping reveals a c.18 degree variation in crystallographic orientation that comprises both a gradual change in orientation and a series...

We derive general analytical expressions relating the equilibrium fluctuations of a grain boundary to key parameters governing its motion coupled to shear deformation. We validate these expressions by molecular dynamics simulations for symmetrical tilt boundaries and demonstrate how they can be used to extract the misorientation dependence of the grain-boundary mobility. The results shed light ...

The roles of grain boundaries and twin boundaries in mechanical properties are well understood for metals and alloys. However, for covalent solids, their roles in deformation response to applied stress are not established. Here we characterize the nanotwins in boron suboxide (B6O) with twin boundaries along the {0111} planes using both scanning transmission electron microscopy and quantum mecha...

An ultrafine/nano grained AZ31 magnesium alloy was produced through four-pass ECAP processing. TEM microscopy indicated that recrystallized regions included nano grains of 75 nm. Pole figures showed that a fiber basal texture with two-pole peaks was developed after four passes, where a basal pole peak lies parallel to the extrusion direction (ED) and the other ~20° away from the transverse dire...

Molecular dynamics deformation studies of nanocrystalline metals suggest a plasticity mechanism where dislocations are nucleated at grain boundaries (GB), travel through the grain being hindered by local GB stress intensities, to be finally absorbed in the surrounding GBs [1][2]. Recent constant strain rate molecular dynamics simulations of nanocrystalline Al demonstrated that dislocations can ...

The large fraction of material residing at grain boundaries in nanocrystalline metals and alloys is responsible for their ultrahigh strength, but also undesirable microstructural instability under thermal and mechanical loads. However, the underlying mechanism of stress-driven microstructural evolution is still poorly understood and precludes rational alloy design. Here we combine quantitative ...

a review on the microstructural evolution in magnesium alloys during severe plastic deformation waspresented. the challenges deserved to achieve ultrafine/ nanostructured magnesium were discussed.the characteristics of the processed materials are influenced by three main factors, including i)difficult processing at low temperatures, ii) high temperature processing and the occurrence ofdynamic r...