Superplastic behavior of fine-grained Al-Mg-Li alloy

The superplastic behavior of fine-grained 1420 Al-Mg-Li alloy was investigated using a modern electron microscopy technique based on automatic analysis of electron backscattered diffraction patterns (EBSD analysis

EBSD study of superplastically strained Al-Mg-Li alloy

In this study, electron back scatter diffraction (EBSD) was employed to examine the microstructure evolved during superplastic deformation of advanced Al-Mg-Li alloy. In contrast to the widely-accepted conception of superplasticity, the microstructure was found to be characterized by elongated grains, a notable fraction of low-angle boundaries, and a distinct (though a very weak) crystallographic texture. All these observations suggested a significant activity of intragranular slip

Effect of strain on gap discrete breathers at the edge of armchair graphene nanoribbons

Linear and nonlinear vibration modes of strained armchair graphene nanoribbons with free edges are investigated by means of atomistic modeling. It is shown that phonon modes can be divided into two groups, the XY-modes with the displacements of atoms in the nanoribbon plane, and the Z-modes with atomic displacements normal to the nanoribbon plane. Strained nanoribbons possess a sufficiently wide gap in the phonon spectrum of the XY-modes so that a gap discrete breather (DB) can be excited. Large-amplitude DBs exist within the strain range 0.125 < εxx < 0.20. At larger strains an attempt to excite a DB results in breaking of the nanoribbon, while at smaller strains the gap in the phonon spectrum of the XY-modes is either too narrow or absent. DBs can have energy up to 1 eV and the maximal DB energy is larger for smaller strain of the nanoribbon. A possible role of DBs in the fracture of strained graphene nanoribbons at finite temperatures is discussed

Microstructural evolution during superplastic deformation of Al-Mg-Li alloy : dynamic recrystallization or grain-boundary sliding?

In this work, advanced capabilities of electron backscatter diffraction (EBSD) were applied to evaluate the role played dynamic recrystallization during superplastic deformation of a typical fine-grained material. It was found that the dynamic recrystallization occurred only locally and thus provided only minor contribution to microstructural evolution. Hence, the preservation of the nearly-equiaxed grain morphology, inherent to the superplasticity phenomenon, cannot be attributed to the dynamic recrystallization

Evolution of supersonic 2-crowdion clusters in a 3D Morse lattice

The rapid development of new technologies is often associated with the realization of nonequilibrium states in materials, in which new mechanisms of structure evolution, different from the traditional ones, can arise. One example is the formation of crowdions, that is, interstitial atoms located in close-packed atomic rows. Crowdions can move at subsonic or supersonic speeds. It has previously been demonstrated that supersonic crowdion clusters are much more efficient at transferring mass than classic supersonic crowdions. This work presents an analysis of the propagation of supersonic crowdion clusters in parallel close-packed atomic rows in an fcc Morse crystal. Supersonic 2-crowdions are excited in four close-packed atomic rows, between which there is one close-packed row, which is not initially excited. The counterintuitive formation of a vacancy in the inner atomic row was observed rather far from the point of excitation. The distance between the vacancy in the inner row and the initiation point depends on the initiation energy. The mechanism of vacancy formation is described. The results obtained can be useful for analyzing the rearrangement and accumulation of defects in materials under extreme conditions

Composition and Microstructure of the Al-Multilayer Graphene Composites Achieved by the Intensive Deformation

The paper presents results of the studies concerning aluminum-graphene composites produced with use of step technique; first mechanical alloying of Al and graphene powders and later intensive deformation by the high pressure torsion. As a result small, thin and round samples of composites, about 10 mm in diameter were achieved. For comparison similar samples not containing graphene were investigated. The X-ray diffraction, transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy were applied to study composites structures and analyze graphene content and atomic bonds. The Raman spectroscopy method suggested multilayer graphene, which could also be identified as the defected nano-graphite as a component of the composite structure as well as some small content of the aluminum carbides. The highly dispersed microstructures of aluminum matrices were identified with the transmission electron microscopy, showing difference between the samples produced with the increased number of rotations, leading to the increased deformation realized. This method revealed carbon and aluminum oxides in large amounts which is interpreted as a surface effect. This method suggested also formation of the carbon-metal and carbon-metal- oxygen atomic bonds, which might partially result from formation of the carbides