Dislocation arrangements in aluminium deformed in tension or by fatigue

Abstract

Abstract A comparison has been made of transmission electron microscope observations on polycrystalline aluminium deformed in tension or by fatigue. The dislocation distribution in aluminium deformed in tension, was studied as a function of stress. At stresses up to 3 kg mm−2 the distribution is extremely irregular; at higher stresses up to the fracture stress, polygon boundaries are formed which become increasingly well developed with increasing stress. Observations have been made on specimens fatigued at high stress, giving a life of 105 cycles, and low stress, giving a life greater than 106 cycles. The dislocation distribution in the former is similar to that in the unidirectionally deformed specimens. The low stress fatigue specimens show two new features. Firstly, polygonization does not occur despite a high dislocation density, and secondly a high density of dislocation loops similar to that found in quenched specimens is observed in some areas. The latter observation suggests the formation of large numbers of point defects during fatigue.