Characterization of Al-8090 superplastic materials using orientation imaging microscopy

A fundamental understanding of the deformation mechanisms of superplasticity requires a detailed characterization of the microstructure. For certain studies, optical microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques used in conventional mode may be inadequate for detailed analysis. This paper presents the use of a newly developed technique, `orientation imaging microscopyʹ (OIM) in characterizing the microstructure of an Al-8090 alloy deformed in uniaxial tension to strains of 15, 70 and 660% at 520°C and 5×10−4 s−1 strain rate. In OIM the microstructure is constructed from the measured crystal orientations obtained from points on the specimen surface distributed in a hexagonal grid. Neighboring measurements with a misorientation greater than a specified value, ω, misorientation angle criteria (designated by the researcher) are deemed to define the location of grain boundaries. These boundary lines can be interpreted as high angle grain boundaries or subgrain boundaries depending on the value of ω. The implications of the analyses on superplastic deformation are discussed.