Micromechanical investigation and phenomenological modeling of Al-8090 superplastic materials

In spite of its great technological importance, our understanding of the phenomenon of superplasticity is incomplete in several critical respects. It is believed that superplasticity occurs as a result of grain boundary sliding which results in changes in microstructure and reduction of texture. However, there is a reoccurring controversy over the accommodation mechanisms which facilitates the process and its interaction with grain boundary sliding. Recent advances in electron microscopy methods have improved the ability to analyze the microstructure of deformed materials. This paper presents the results obtained primarily from the application of one of such techniques, Orientation Imaging Microscopy (OIM), in the study of microstructural evolution in superplastically deformed AI-Li materials. The OIM technique incorporates automatic analysis of electron backscattered diffraction patterns with precise movement of a computer-controlled stage to produce accurate measurement of lattice orientation. The data can be reconstructed to produce grain boundary maps, which is a form of microstructure representation. The analysis of these maps revealed the complexity of the processes involved in the formation of high and low angle boundaries in superplastic materials. An attempt was made to correlate these misorientation data to the mechanical response of the superplastic material through a phenomenologically based model.