Local Lattice Instability Analysis on Stability Switching in Amorphous Nickel
Masaomi NISHIMURA, Kisaragi YASHIRO and Masahiro ARAI
Abstract:We have so far shown that amorphous metals have many ``unstable'' atoms even at the equilibrium state, by local lattice instability analysis (LLIA) which discusses the positive definiteness of atomic elastic stiffness coefficients, Bƒ¿ij. In the present study, we put our focus on the stability switching by the ``probabilistic'' fluctuation and the ``deterministic'' mechanical load. We have performed molecular dynamics simulations on Ni amorphous and evaluated the stability switching under no-load equilibrium as well as uniaxial tension. It is definitely true that the ratio of unstable atoms decreases/increases according to the system energy; however, it is revealed that one-way change of stabilization or destabilization never occur but both positive and negative stability-switching are activated from their ratio under the equilibrium state. That is, a straightforward image of ``stabilization/destabilization of local configuration'' is not correct for structural change in amorphous metal but ``shuffle of atomic arrangement'' which involves atomic stabilization and destabilization simultaneously. In fact, we have proved that (1) both switching drastically increase at the slow-down point just before the stress-strain peak, (2) many stabilization/destabilization atoms can be found in the locally deformed area, and (3) such switching atoms actually feel hydrostatic tension in the dilated local configuration on the way of ``shuffle''. Key Words:Local lattice instability analysis, Molecular dynamics simulation, Amorphous metal, Stability switching, Structural change