Relationship between deformation and stability switching in amorphous metal : local lattice instability analysis

We have attempted to comprehend the deformation behavior of amorphous metals by the local lattice instability analysis that discusses the positiveness of atomic elastic stiffness coefficients, Bα ij, or the second-order derivatives of atomic energy composition. In the present study, we discuss the stability-switching, or transitions between detBα ij ≥ 0 and detBα ij < 0, by the “probabilistic” fluctuation and the “deterministic” mechanical load. No-load equilibrium, tension, compression and simple shear are performed on an amorphous nickel by molecular dynamics simulations. The positive and negative stability-switching, or “stabilization” and “destabilization”, occur due to the “probabilistic” fluctuation even at the equilibrium state. The number of detBα ij < 0 atoms shows almost constant while the distribution of detBα ij < 0 atoms indicates different morphology at each observation time. Ratios of switched atoms with stability-switching under tension, compression and shear are larger than that under the equilibrium because the local structural relaxation produces simultaneously both positive and negative stabilityswitching. Atoms with negative and positive stability-switching show increases and decreases of atomic volume, respectively; while only positive switching shows the decreases in local volumes, evaluated with the atomic volumes of surrounding atoms within the cutoff radius, according to the incidence of “deterministic” structural changes

Molecular dynamics simulations on interaction between dislocation and Y2O3 nanocluster in FE

For a new insight on the mechanical properties of oxide dispersion strengthened (ODS) steels from atomistic viewpoints, we have implemented molecular dynamics simulations on the interaction between Y2O3 nanocluster and dislocation in bcc Fe. There is so far no all-round interatomic potential function that can represent all the bonding state, i.e. metal, ion and covalent systems, so that we have adopted rough approximation. That is, each atom in Y2O3 is not discriminated but treated as “monatomic” pseudo-atom; and its motion is represented with the simple pairwise potential function as same as Johnson potential for Fe. The potential parameters are fitted to the energy change in the hcp infinite crystal, by using the ab-initio density functional theory(DFT) calculation for explicitly discriminated Y and O. We have set edge/screw dislocation in the centre of periodic slab cell, and approached it to the “YO” monatomic nano-cluster coherently precipitated in bcc-Fe matrix. The dislocation behavior is discussed by changing the size and periodic distance of the nano-cluster. Among the many useful results, we have obtained a conclusion that the edge dislocation is strongly trapped by YO sphere larger than the diameter of d =0 .9nm, while the screw dislocation shows various behavior, e.g. it cuts through the precipiate without remarkable resistance if the dislocation line tension is high, or it changes the slip plane leaving jogs at the position anterior to the precipiate with loose line tensio

Relationship between deformation and stability switching in amorphous metal : local lattice instability analysis

We have attempted to comprehend the deformation behavior of amorphous metals by the local lattice instability analysis that discusses the positiveness of atomic elastic stiffness coefficients, Bα ij, or the second-order derivatives of atomic energy composition. In the present study, we discuss the stability-switching, or transitions between detBα ij ≥ 0 and detBα ij < 0, by the “probabilistic” fluctuation and the “deterministic” mechanical load. No-load equilibrium, tension, compression and simple shear are performed on an amorphous nickel by molecular dynamics simulations. The positive and negative stability-switching, or “stabilization” and “destabilization”, occur due to the “probabilistic” fluctuation even at the equilibrium state. The number of detBα ij < 0 atoms shows almost constant while the distribution of detBα ij < 0 atoms indicates different morphology at each observation time. Ratios of switched atoms with stability-switching under tension, compression and shear are larger than that under the equilibrium because the local structural relaxation produces simultaneously both positive and negative stabilityswitching. Atoms with negative and positive stability-switching show increases and decreases of atomic volume, respectively; while only positive switching shows the decreases in local volumes, evaluated with the atomic volumes of surrounding atoms within the cutoff radius, according to the incidence of “deterministic” structural changes

Possibility of Fabricating Anisotropic Conductive Film with a Line-and-Space-Like Pattern by Stick-Slip Accompanying Abrasion

The development of an anisotropic conductive film was attempted using original microfabrication (stick-slip (SS) processing) involving SS accompanying abrasion. During SS processing, the film surface was periodically scraped with a razor. For a metal-deposited polyethylene terephthalate (PET) film (metal/PET film), fine periodic structures (line and space (L/S)-like patterns) were formed on its surface because the metal layer was periodically scraped. This result proved that SS processing can be applied not only to polymers but also to metals. Moreover, the line interval of an SS-processed metal/PET film shortened as the contact force decreased, and the depth of the line became shallower in proportion to the line interval. In addition, SS-processed copper/PET (Cu/PET) film did not conduct electricity in the direction perpendicular to the Cu line; however, it conducted electricity in the direction parallel. Thus, this study shows the possibility of using SS processing for fabricating an anisotropic conductive film

Buckling simulation of single crystalline Mg nanowaire: eigenvalue and eigenvectors of atomic elastic stiffness at onset of bending

In order to reveal the precursor of buckling by the eigenvalue/vectors of the atomic elastic stiffness, Baij = Δσai/Δεj (atomic stress and strain in the Voigt notation), molecular dynamics simulations are performed on a single crystalline Mg nanowire of 5nm×5nm×104nm (infinite bar under periodic boundary) with the three compressive directions of the [0001], [1210] and [1010]. The corner atoms of the nanowires show negative 1st eigenvalue, ηa(1) (the solution of the eigen-equation of {Baij}{Δεj} = ηa{Δεi}), or “unstable” in the initial equilibrium; and the other atoms never become ηa(1) &lt; 0 at the onset of bending. Thus we investigated the distribution of the ηa(1) in each corner and found that the position of the minimum ηa(1) was close to the peak point of the Euler buckling curve. The deformation modes of these unstable corner atoms are also visualized by the maximum principal strain direction calculated by the strain compornent of the corresponding eigenvectors, {Δεi} = {Δεxx,··· ,Δγxy}T