In situ observation of stress-induced structural disorder and fictive stress in a Zr55Al10Ni5Cu30 glassy alloy

The heat evolution of stress-induced structural disorder, DeltaH(s)(t), in a Zr55Al10Ni5Cu30 glassy alloy during creep deformation under a constant load at the glass transition region (T-g = 680 K) is investigated by an in situ measurement of temperature change of a deforming sample. For an initial stress, sigma(0), greater than a critical stress, sigma(c) = 80 MPa, all DeltaH(s)(t) curves grow gradually attaining a maximum then decrease with further deformation. The peak in Al, indicates the attainment of an equilibrium flow structure. The DeltaH(s) curves plotted against the logarithm of normalized viscosity (ratio of viscosity, eta, to the Newtonian viscosity, eta(N)) tend to merge and increase linearly with a slope of -500J/mol, as established previously for the steady-state flow state. The present result implies that the same relationship between the structural disorder and viscosity is applicable in the transient flow state as well as in the steady-state flow state. There exists a fictive stress, or steady-state flow stress, which indirectly represents a glass structure. It is also shown that the fictive stress, sigma(f), can describe the free volume, vf, as well as the 77 and DeltaH(s) of a glass experiencing various stress deformations.