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Hydrogen Effects on Dislocation Motion in BCC Iron: Hybrid Quantum and Classical Simulation

Ryo Kobayashi (Nagoya Institute of Technology), Tomoyuki Tamura (Nagoya Institute of Technology), Shuji Ogata (Nagoya Institute of Technology)

Joint Session: Discrete Dislocation Plasticity and From Atomistics to Reality: Spanning Scales in Simulations and Experiments

Mon 2:40 - 4:00

CIT 227

Hydrogen embrittlement in iron and steels is still one of the most important problems in the field of industrial structural materials even though it has a long history over hundred years. There are several mechanisms that have been suggested during the history related to the various states of hydrogen atoms in bulk iron. However, since hydrogen atoms are small and light, and crack propagations and dislocation emissions at the crack tip are very fast phenomena in the material, it is difficult to observe the hydrogen states and dynamic phenomena around the crack tip. And it is believed that in a certain temperature range hydrogens enhance dislocation mobility in bcc iron, because hydrogens lower bonding strength of iron atoms and change local shear modulus around the dislocation core. But there is no direct evidence that the chemical effect of hydrogen is the reason for lowering the migration barrier of dislocation. The difficulty of studying the hydrogen effect on dislocation motion from the point of view of atomistic simulation is the multiscaleness of this problem; the chemical effect of hydrogen which is a quantum mechanical phenomenon and the boundary condition for the dislocation core correlate, and it is not easy to handle these phenomena accurately at the same time. We have performed hybrid quantum and classical (QMCL) simulation, which allows us to calculate dislocation core structures and hydrogen effects by the accuracy of ab-initio calculation and to consider long-range displacement field around dislocations, to investigate the hydrogen effects on the energy barriers of dislocation migration. And comparing the effects of hydrogens and helliums, we have evaluated the checmial contribution and elastic contribution of hydrogens to the migration barrier of dislocation. We will discuss details of calculation method and results in the presentation.