Molybdenum is an excellent material for use in demanding high temperature applications. However, its fracture behaviour at ambient temperatures is significantly influenced by the microstructure (e.g. size and shape of the grains, annealing condition etc.) and the content of impurities at grain boundaries. Since the 1960ies researchers assume and discuss, that for example alloying elements as boron and carbon segregate to the interfaces and may strengthen the grain boundary.
To study such segregation behaviours high resolution analytical techniques, such as atom probe tomography (APT) and transmission electron microscopy (TEM), are required.
Nevertheless, for APT investigations a site-specific specimen preparation is necessary to study the grain boundary chemistry effectively. With the novel method of transmission Kikuchi diffraction (TKD), supporting focused ion beam (FIB) preparation, a grain boundary can be positioned in the first 200 nm of an atom probe sample without using the TEM. Furthermore, the high resolution technique of TKD gives the opportunity to get crystallographic information of the mapped area and, therefore, an analysis of the grain boundary character.
In the present APT-study grain boundaries of carbon- and boron-doped sintered molybdenum alloys are compared with technically pure molybdenum. Additionally, the microstructure is analyzed by electron backscatter diffraction (EBSD) as well as TEM and the mechanical properties are determined by nanoindentation. The difference of segregation content at the grain boundaries is discussed.
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