High resolution surface studies of superplastic deformation in shear and tension

Abstract

AbstractDespite decades of study, the fundamental mechanisms of superplasticity, particularly relating to the accommodation of grain boundary sliding, are still widely disputed. This is partly due to a lack of information on individual grain deformation and sliding events. Previous studies of superplasticity using surface markers have tended to use either diamond paste scratches, which make quantitative measurements difficult and are open to widely varying interpretation, or regular grids with spacing greater than the grain size, which prevents measurements of intragranular deformation. Recent work has shown that a Focussed Ion Beam (FIB) can be used to create regular, repeating grid marker systems with pitches varying from 0.25 to more than 50 microns. Previously published results in Sn‐Pb have shown the power of this technique, particularly regarding the lack of intragranular deformation and surface grain boundary sliding accommodation mechanisms. The current study has applied the FIB technique to Al5083, a pseudo‐single phase alloy. Tensile tests have been performed with elongations from 5 % to 150 %. Additionally, analogous biaxial shear tests have been performed for comparison and to limit the free surface effects. SEM images of FIB markers before and after deformation have been acquired, and quantitative measurements of the localized strains have been made using 3‐D tilt reconstruction. Shear and tension results show several distinct features. However, no significant intragranular deformation is seen under either set of strain conditions. Possible accommodation mechanisms are discussed.