An appropriate beam of ions can be used to accurately machine samples. This is usually done by creating a sharp tip of liquid gallium. The application of an electrical field causes the emission of gallium ions, which on hitting the sample cause the removal of material. There are other effects, such as the emission of secondary electrons, which can be used to form an image in a scanning electron microscope. The ability to accurately machine and image in a scanning electron microscope can be exploited in many different ways.
In this work, Michael Uchic (AFRL, USA) has investigated the three-dimensional shapes of grains in a nickel based superalloy IN100. The nominal chemical composition in Ni-17.1Co-13Cr-10Al-1.82Mo-4.93Ti-0.84V-0.1B-0.31C-0.034Zr at.%.
The first movie is an accumulation of images taken by successively removing slices of material. It is the equivalent of serial sectioning in order to investigate three-dimensional form. The straight features are annealing twins.
The second movie uses the same process but this time the pictures are created using orientation imaging. The colours therefore represent different crystallographic orientations. This removes any ambiguity regarding the definition of a grain.
The movies and associated information have been provided by Michael Uchic of the Air Force Research Laboratories, Wright-Patterson Air Force Base, USA for educational purposes.
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