Experimental Investigation of Deformation Mechanisms Present in Ultrafine-Grained Metals

Ultrafine-grained (UFG) metals possess grain sizes on the order of hundreds of nanometers and display a remarkable capacity for high strength, high ductility, and enhanced superplasticity. This paper presents the preparatory steps necessary for a highresolution experimental investigation into the deformation mechanisms active in UFG metals. A new experimental methodology is used, in which an optical metrology known as Digital Image Correlation (DIC) is combined with scanning electron microscopy to track the quantitative development of full-field strains on the length scale of the microstructure. The micro-scale field of view and use of a SEM for image capture require the development of novel specimen patterning methods and of image distortion corrections prior to experimentation. The results obtained through the combined SEM and DIC approach, and corresponding pre- and post-mortem electron backscatter diffraction (EBSD) analysis, enable the analysis of the real-time, micro-scale evolution of Lagrangian strains at an unprecedented spatial resolution, and the quantification of the surface deformations inside grains and across grain boundaries as the material is subjected to thermo-mechanical loading.