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Nanotwinned exist in crystals as coherent interfaces with low interfacial energy, which can not only improve the strength of metal materials, but also increase the ductility. In this manuscript, we have performed molecular dynamics simulations of the mechanical properties of a nano-columnar crystalline Cu-Ni alloy with different twin boundary spacing. It is found that the model without twin has a stacking fault tetrahedron composed of stair-rod dislocations, which results in a small change in dislocation density at the later stage of deformation, and the average stress after yielding is lower than that of the model with twin. During the deformation process, with the increase of Other atoms, the dislocation slip barrier is enhanced, the tensile strength is increased, and the yield phenomenon is delayed, which is more obvious with the decrease of twin boundary spacing. The dislocation density decreases with the decrease of the spacing of the twin boundary, and the dislocation segments become shorter. When the twin boundary spacing is 0.625 nm, the tensile strength is increased by about 71% compared with the model without twin structure. [ABSTRACT FROM AUTHOR]

The tensile fracture behavior of the annealed 316L austenitic stainless steel at room temperature was studied by in-situ tensile platform loaded on the field emission scanning electron microscope with 4.2e−4 s−1 of initial strain rate. The results showed that tensile strength and yield strength of annealed specimens of 316L for annealing treatment for 28 h at 800 °C were higher than those of as-cast specimens. After annealing, microstructures of the specimens were mainly micron crystals. When the applied loading was 162 MPa, initiation source appeared. Loading reached 380 MPa, main cracks continued to expand and became deeply, and specimen yielded at this time. When loading reached up to 533 MPa, specimens reached the maximum stress value. After breaking completely, included angle was approximately 70° between fracture surface and direction of tensile axis. The composition of the fracture was more pure and continuity of the matrix was good. This showed that micro/nanostructure stainless steel prepared by aluminothermic reaction casting, which could improve the mechanical properties through controlling size of nanocrystalline and microcrystalline austenite grains and their volume fraction. [ABSTRACT FROM AUTHOR]

An inverse “smaller is stronger” trend is predicted on the basis of molecular dynamics simulations of α-titanium (Ti) single-crystal nanopillars orientated for double prismatic slips when the nanopillars are less than 7 nm wide. This trend is attributed to a significant increase in the surface energy due to the nucleation and propagation of edge dislocations on the surface of the pillars. [ABSTRACT FROM AUTHOR]