Multiscale modeling and experimental determination of the intergranular fracture strength of transition metals in the presence of carbon
Arshad Tahir (ICAMS Ruhr Universität Bochum, Germany), Rebecca Janisch (ICAMS Ruhr Universität Bochum), Alexander Hartmaier (ICAMS Ruhr Universität Bochum)
From Atomistics to Reality: Spanning Scales in Simulations and Experiments Symposium B
Tue 2:40 - 4:00
CIT 227
Grain boundaries play an important role during plastic deformation and failure of poly-crystals. In case of the refractory metals, e.g. molybdenum and tungsten, which are the materials of interest in high-temperature applications, the reduction of strength due to grain boundary embrittlement is especially large. The presence of defects at the grain boundaries affect their mechanical properties, which in turn alter the hardness or fracture toughness of poly-crystals favorably or adversely. Carbon as a point defect has been reported to increase the strength of grain boundaries in body centered cubic metals. In order to investigate the strengthening effect of carbon at grain boundaries, a systematic study of a 5 (310)[001] symmetrical tilt grain boundary (5 STGB) in molybdenum, tungsten and iron has been carried out. Atomistic scale uni-axial mechanical tests with loads perpendicular to the grain boundary were performed for all the aforementioned systems using ab-initio density functional theory (DFT) calculations. The results show an increase in the theoretical strength with carbon in all cases. Electronic structures have been analyzed to understand the effect of carbon on the grain boundary strength. From the DFT uni-axial mechanical test results, traction separation data has been derived that is being used for the parameterization of a cohesive zone model to predict inter-granular fracture at the continuum level using finite element analysis. In addition, the results of in-situ micro-cantilever beam experiments on molybdenum bi-crystal samples with and without carbon at the grain boundary will be presented.