The role of the surface layer on the power law breakdown in high temperature creep

Abstract

The dislocation density as computed from X-ray line-broadening analysis was measured in the surface layer, i.e. π s, and in the interior, i.e. π i, of aluminum alloy 1100 specimens crept at high temperatures. The power law breakdown occurred when π s > π i. In the power law breakdown region, π s increased rapidly with strain and stress while π i increased incrementally to higher plateau levels as the stress was increased. The decrease in dislocation density on annealing after creep consisted of two stages: a rapid stage with an activation energy of 14.3 kJ mol −1 and a slower stage with an activation energy of 127.9 kJ mol −1. The recovery process was the same for specimens crept within and above the power law region.