EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Mechanical properties of metallic materials, such as strength and ductility, strongly depend on the microstructure. In technically pure materials, grain boundaries are the most important microstructural feature and might cause crack initiation. In molybdenum, a much used refractory metal, beside intrinsically weak interfaces, grain boundary cohesion is further influenced by impurities. Due to the low solubility of interstitials in the molybdenum matrix, elements like oxygen, carbon or nitrogen segregate to the grain boundaries. It is well known that oxygen has a detrimental effect, whereas carbon and/or boron show a beneficial effect on grain boundary cohesion. An advanced approach, so-called segregation engineering, is the introduction of small amounts of cohesion enhancing elements segregating to the grain boundaries to improve material performance.
To analyze early stages of intergranular crack formation, three-point bending tests on recrystallized commercially pure and boron micro-doped molybdenum were conducted between -28°C and room temperature. The specimen surface, subjected to tensile stress during bending, was examined post-mortem close to the final fracture plane by scanning electron microscopy. The occurring, mainly intergranular, separation of grains is investigated for distinct features, such as the crystallography of involved grains and length of grain boundary cracks. Necessary requirements for a direct comparison between the material variants and the effect of boron doping are discussed.