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 noncorrela ted two-stage elementary shear atomic rearrangements with continuously distributed activation parameters in distinct regions of structure-re laxation centres. In loaded samples structural relaxation results in a n 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 struct ural relaxation. Specially designed experiments were performed to test the theory. It is shown that the theory gives an adequate interpretat ion of experimental creep kinetics except for the lime interval that c overs 10(1)-10(2) s after loading. This initial creep stage is suppose d to result from reversible atomic rearrangements in relaxation centre s with a symmetrical two-well potential. (C) 1998 Acta Metallurgica In c.