Microstructure of aluminium during creep at intermediate temperature—II. In situ study of subboundary properties

Abstract

The aim of this study is to work out a microscopic picture of the second stage of creep at intermediate temperatures. The dislocation networks having been described in a previous article, we report here subboundary properties under load during in situ experiments on predeformed specimens, in the high voltage electron microscope. Subboundary formation, migration and destruction take place during creep. The two former processes occur frequently and ensure a constant average subgrain size under constant stress. They also play a key-role during transients. For subboundaries with three coplanar Burgers vectors, and in the case of pure tilt, migration occurs by glide of the dislocation segments. Those with two orthogonal Burgers vectors and equal dislocation spacings remain immobile or are destroyed in the absence of significant climb. Triple junctions are also mobile. Subboundary migration accounts for about 10% of the creep strain. The creep rate is therefore bound to the movement of individual dislocations which will be described in another article.