The role of non-equilibrium grain boundary in micro-deformation and failure mechanisms of Bicrystal structural tungsten

P Li and LS Wang and SL Yan and M Meng and YF Zhou and KM Xue, INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 94, 105376 (2021).

DOI: 10.1016/j.ijrmhm.2020.105376

The molecular dynamics (MD) simulation is performed to obtain the mechanical properties and plastic de-formation mechanism of bicrystal structural tungsten (BS W) with equilibrium grain boundaries (EGBs) and non equilibrium grain boundaries (NEGBs) under tension at different strain rates. The BS W with NEGBs has shown excellent comprehensive mechanical properties, and its yield strength is only about 1.5 Gpa (similar to 10%) lower than that of the BS W with EGBs. The yield strain of BS W with NEGBS is about double than that with EGBs. The micro- deformation mechanisms for BS W with NEGBs under tension are dislocation emission and movement, GBs interaction, and phase transition. However, the failure modes of BS W with EGBs are intergranular brittle fracture of crack near the GBs, and the strain rate has little effect on the fracture. The phase transition mechanism for BS W with NEGBs under the tension loading strain rate of 0.0001 ps(-1) is atomic slippage, but that of 0.001 ps(-1) is stress concentration induced quasi- reconstructive phase transition. At the loading strain rate of 0.0001 ps(-1), dislocation emission and movement to the GBs would form the non- slippable crack dislocations for crack initiation. However, at the loading strain rate of 0.001 ps(-1), the crack propagation is considered as a zigzag-shaped form on account that the phase transition induced stress relaxation. The NEGBs could improve plasticity without sacrificing strength, providing a theoretical method for nano-structure design, material modification, and sustainable material plain.

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