A method for measuring microstructural-scale strains using a scanning electron microscope:: Applications to γ-titanium aluminides

This article introduces a new technique for measuring strains on the scale of the microstructure using a scanning electron microscope (SEM) and an in-situ tensile stage. A grid of markers is deposited on the polished surface of a tensile sample. The method then compares a reference image of the undistorted material with an image taken after deformation. A convolution operation determines the location of each of the markers in both images, from which the marker displacements and surface strains follow. Displacement accuracies of 0.01 image pixels are attainable. We have applied this method to cast gamma-TiAl-based alloys. The properties of these alloys depend sensitively on the microstructure, which can vary widely in morphology and scale. The surface-displacement mapping technique is effective for identification of microstructural features that affect the local straining and resulting properties in this class of intermetallics.