Imagining and Imaging- Examples from Materials Science

Structures and many related concepts in material systems were originally “visualised” by human imagination. Materials scientists are not satisfied by only validating these concepts on the basis of fundamental physical laws but attempt to image them for comparing their imagination with realities. This point will be elaborated citing several examples. It will be shown that modern electron microscopic and atom-probe techniques can indeed image structures in different length scales right upto atomic dimensions. Such observations not only confirm the relevant ideas proposed earlier but also provide a new insight into the governing phenomena. Examples will include dislocations in complex alloys with unit cells containing several hundred atoms, internal twinning of martensite, ordered structures of grain boundaries, partial collapse of lattice planes in a displacement ordering process and atom positions in an interstitially ordered alloy.