Isothermal creep of metallic glasses: A new approach and its experimental verification

An extended version of the theory of structural relaxation in metallic glasses under the action of external stress is presented. The theory explains the structural relaxation as a set of irreversible noncorrelated two-stage elementary shear atomic rearrangements with continuously distributed activation parameters in distinct regions of structure-relaxation centres. In loaded samples structural relaxation results in an accumulation of plastic deformation in accordance with magnitude and orientation of the applied stress. General equations are obtained for the creep strain rate as a result of the irreversible directed structural relaxation. Specially designed experiments were performed to test the theory. It is shown that the theory gives an adequate interpretation of experimental creep kinetics except for the lime interval that covers 10(1)-10(2) s after loading. This initial creep stage is supposed to result from reversible atomic rearrangements in relaxation centres with a symmetrical two-well potential. (C) 1998 Acta Metallurgica Inc.