“…3,10,27,30,34,39,40,[46][47][48] Moreover, the strain rate is a square or cube function of the inverse grain size (p ϭ 2-3), and the activation energy is approximately that for grain boundary diffusion (Q ϳ 45-55 kJ/mole), as expected for deformation that is dominated by GBS. [33][34][35][36][37][38]43,46,49,50 Region I behavior is observed at low stress, ordinarily 1 MPa or less. At some sufficiently low stress one would expect to find deformation dominated by diffusional creep processes, 22,32 as noted, for example, in the limited area of diffusional creep in Ashby's deformation-mechanism map for pure lead.…”