Quantitative surface topography of martensitic microstructure by differential interference contrast microscopy

We theorize a mathematical model by which the topography and the full-field deformation of martensitic microstructure are quantitatively determined by the reflected light differential interference contrast microscopy technique. Using the commercial reflected light DIC microscope (Nikon Ni-U), we determine the optical parameters for the proposed mathematical model using calibrated standard samples. Based on the theory, we conduct an experiment to demonstrate the determination of the surface relief of the microstructure comprised of a pair of twinned martensitic variants. The surface height gradients of the two martensite variants along the beam-shear direction of DIC agree well with the values measured by the atomic force microscopy. The measured results of twin laminates reveal that the current microscopy system can resolve the microstructure with the fineness of around 500 nm. Compared with the AFM results, it measures the surface slope with 0.005 rad accuracy. This paper underlies a new approach for quantitative surface topography determination with wide applications in experimental mechanics. (C) 2018 Elsevier Ltd. All rights reserved.