The heat evolution of stress-induced structural disorder, ΔHs(ε),
of a Zr55Al10Ni5Cu30
bulk metallic glass (BMG) during compressive constant ram-velocity deformation at the glass transition region (Tg = 680 K)
was deduced from in situ
measurements of temperature change of the deforming sample. At the transition from the linear to nonlinear viscoelasticity, the behavior of viscosity change with strain, η(ε), is qualitatively consistent with the enthalpy evolution of the structural disordering, ΔHs(ε),
but not with the temperature change, ΔT(ε).
It is concluded that the initial softening deformation is due to the stress-induced structural disordering. The change in the nonlinearity, −log ≡ −log η /ηN,
is found to be proportional to the ΔHs
and the slope of ΔHs(−log )
can be estimated to 400 J/mol, where ηN
is the Newtonian viscosity. On the other hand, the temperature raise, ΔT(ε),
is pronouncedly delayed as compared with the η (ε) and ΔHs(ε)
at the transition, but is determined by a product of stress and plastic strain-rate, σ⋅p,
and is nearly proportional to it at the steady state. The slope of ΔT(σ⋅p)
can be estimated to 5.2×10−2 K mol/W.
© 2003 American Institute of Physics.