Activation entropy and enthalpy of creep in pure metals.

• Shear strain rate should be the independent variable in creep. • Dislocation creep is due to a single deformation mechanism not two. • Activation entropy is a component of the flow activation energy. • Results lie on similar activation energy – temperature curves. Previously published results on the power law creep of a selection of fcc, bcc and hcp pure metals are discussed using a modified Stokes – Einstein equation originally describing Newtonian viscosity of spherical particles in a fluid. Activation energy is modified to include terms representing activation enthalpy, activation entropy and the effect of strain rate. It is similar to the Dorn equation for power law creep but with strain rate rather than stress as the independent variable. Curves of activation energy vs shear rate are linear rather than having a discontinuity as have those with stress as independent variable. All metals have linear curves of activation energy at zero rate vs temperature, the slope of which reflects the activation entropy and is similar for all metals. Intercepts which represent activation enthalpy are dependent on lattice structure. [ABSTRACT FROM AUTHOR]