Microstructure of aluminium during creep at intermediate temperatures—III. The rate controlling process

Abstract

The aim of this study is to work out a microscopic picture of the second stage of creep of aluminium at intermediate temperatures. The substructure and its evolution during creep having been described in the two former articles, we detail here the movement of individual dislocations responsible for the main part of deformation, during in situ experiments in a high voltage electron microscope. The mobile dislocations are emitted by sources situated inside a few subgrains. They have to cut through subboundaries, and this appears to be the rate controlling process. This mechanism which is described as insertion followed by extraction, is studied in detail, as well as annihilation of mobile dislocations in other subboundaries. It is easier than the Orowan process, and it involves cross slip, but no climb. However, the stress necessary is higher than the applied stress, so that extraction requires high local forward internal stresses in subboundaries. The different types of recovery observed—static and dynamic—are discussed, and it is concluded that cross slip is the rate controlling mechanism of creep of aluminium at intermediate temperatures.