Abstract
It is revealed 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, Bαij. We have explored for relationships between the deformation and these unstable atoms in inhomogeneous or disordered structure. In the present study, we have discussed the changes in unstable atoms of det Bαij < 0 in four monatomic amorphous metals, Ni, Cu, Zr and Al, during uniaxial tension. First, we have separately evaluated the atomic stress on stable and unstable atoms. Unstable atoms feel hydrostatic compression in the amorphous Ni, Cu and Zr, while they feel hydrostatic tension in the Al at the initial state before loading. Under the uniaxial tension, it is considered from the comparison of stress components on each stable and unstable atoms that the local stress reduction occurs by the transition of stable → unstable in Ni, Cu and Zr, and unstable → stable in Al. Then we have picked up atoms that have actually switched between stable and unstable. Even at the equilibrium state, so many atoms switch their stabilities while the ratios of the negative and positive change nearly balance at each moment. Both positive and negative switching are activated by rises of the structural relaxation under the tension. Moreover, there is no difference in the stress between positive and negative switching atoms while constant detBαij < 0 and detBαij > 0 atoms showdifferent stress. We have concluded that the stress relaxation is not caused by a straightforward image of “stabilization” or “destabilization”, but by “shuffle of atomic arrangement” which involves positive and negative switching simultaneously. In fact, we have observed many incidences of positive and negative stability-switching at the locally deformed area.
