Anisotropy and grain size dependence of the effects of hydrogen on the shock-induced spallation in iron

LX Feng and XQ Zhang and WH Li and MZ Xiang and XH Yao, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, 256, 108536 (2023).

DOI: 10.1016/j.ijmecsci.2023.108536

Hydrogen (H) embrittlement in metals has long been a source of concern in academia and industry. However, the fundamental mechanisms remain not well understood in dynamic events. Using atomic simulations, shock responses of monocrystalline & alpha;-Fe along the 100 and 111 crystal orientations and nanocrystalline Fe with and without H atoms are investigated systematically. For the first time, the anisotropic dependences of the effects of H atoms on the spall strength are revealed. In the case of the 100 crystal orientation, H atoms prevent the phase transition of & alpha;-iron under shock compression, further slowing down the growth of voids during spall fracture and enhancing the spall strength at high strain rates. While in the case of 111 crystal orientation, H atoms promote dislocation formations under shock compression which is consistent with the known hydrogen-enhanced local plasticity (HELP) mechanism; H atoms accelerate the growth of voids during the spallation and reduce loads bearing capacity, which finally lowers the spall strength of & alpha;-iron. In nanocrystalline samples, voids favor along GBs. The presence of H atoms would cause a local disturbance at the GB but block the long-distance movement of the surrounding atoms resulting in a slight increase in spall strength. The combined effects of H atoms and GBs influence the void evolution. This work provides deep insights into the hydrogen effect on metals under dynamic loading and should benefit a wide broad of research communities in materials and mechanics.

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