Influence of shear wave on the HCP nucleation in BCC iron under oblique shock conditions

The HCP nucleation in single crystal iron under oblique shock loading is investigated based on atomistic simulations. The stress profile and microstructure analysis reveal that the critical pressure of HCP nucleation is effectively reduced by applying the shear wave, and even the HCP nucleation can take place below the BCC-HCP equilibrium pressure. Under normal shock, the stress and energy distributions show some difference in the mixed phase, while the introduction of shear wave will change this difference as expected. The second HCP nucleation occurs under the specific strain constraint, which promotes the formation of HCP twins and results in shear deformation localization at the same time. Besides, the shear wave can either increase or reduce the potential barrier of the HCP nucleation, dependent on the shock intensity and shear direction, which indicates the over-pressure of HCP nucletion can be significantly reduced under some strong shear loading. The HCP nucleation stress threshold will first experience a linear change and undergo a significant reduction when the shear instability occurs.