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Abstract
A significant loss of fracture toughness () is induced by intergranular (grain boundary; GB) segregation of metalloid solute in alloy steels. Yet, the mechanism has not been clarified from a multiscale point of view. From a thermodynamic approach aided by first-principles calculations, it is shown that segregated solute with higher energetic stability on fracture surfaces causes a larger linear reduction in the ideal work to intergranular fracture (
); i.e. the energy difference between a GB and its two fracture surfaces. Remarkably, the combined analysis with first-principles calculations and fracture mechanics experiments found several orders of magnitude more energy loss in
for a specific range in the
within only a few tenths of
. These results illustrate that the GB of steel has the threshold energy of atomic cohesion under which catastrophic failure occurs. Our research scheme would play a key role in identifying specific solute elements to toughen the GB in metallic systems used under aggressive environments.
Acknowledgements
The calculations were performed on the supercomputer (Fujitsu BX900) system in JAEA. This study is financially supported by the Elements Strategy Initiative for Structural Materials (ESISM) through the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. We appreciate R. Kameda for assisting with editorial work.