Superplasticity in the aluminium-zinc eutectoid - an early model revisited

Superplastic extension of the aluminium-zinc eutectoid results primarily from grain-boundary sliding and grain rotation. The strain rate ((epsilon) overdot), flow stress (sigma), grain size (L) and temperature (T) are related empirically: (epsilon) overdot = K sigma(2)/L-2 exp[-U/kT]. The following mechanism is in agreement with our observations: (i) Certain grains that obstruct the easy relative motion of groups of grains by grain boundary sliding yield under the resulting stress concentration; (ii) dislocations traverse such yielded grains and pile up at grain boundaries; (iii) the stress at the head of the pile-up causes accelerated diffusion and dislocations escape by climb into and along grain boundaries. The replacement of these dislocations makes possible further boundary sliding. (C) 1997 Elsevier Science S.A.