Microstructural Characterization of Molybdenum Grain Boundaries by Micropillar Compression Testing and Atom Probe Tomography

Molybdenum is part of many modern everyday items and, to some extent, also necessary for their production. Besides its high melting point of 2620 degrees C, molybdenum exhibits good electrical and thermal conductivity and a low coefficient of thermal expansion at the same time. However, pure molybdenum has low ductility at room temperature. The ductile-brittle transition which is typical of body-centred cubic metals occurs at around room temperature, depending on the processing state. Thus, components partly fracture along the grain boundaries due to brittle failure. The decisive reason for this are, inter alia, impurities which segregate at grain boundaries. In order to analyze individual grain boundaries, a load is applied in compression direction to micropillars in the size range of a few micrometres. This allows a targeted study of the mechanical properties, complemented by atom probe experiments analysing the chemical structure. The micrometre-scale analyses enable the determination and correlation of the mechanical with the chemical properties of a single grain boundary with the aim of better understanding the relationship between segregations and deformation behaviour in the grain boundary region.