Shock-induced Structural Phase Transformation in bcc Iron

Shock along Fe-bcc(001), piston velocity=417m/s

Shock waves were initiated by a 'momentum mirror' (B.L. Holian and P.S. Lomdahl, Science 280, 965 (1998)), which specularly reflects any atoms atoms reaching reaching the face of of the perfectly flat infinitely massive piston (left) moving at a piston velocity. The resulting shock waves in the iron single crystal moves (from left to right) along the (001) direction in the initial bcc structure (gray). Above the threshold for the structural transformation (about 15GPa, about 10 percent uniaxial compression, or about a piston velocity of 5 percent of the longitudinal sound velocity) into the close-packed structure (red) many grains of the close-packed material nucleate in a displacive manner (martensitic-like) within the uniaxially compressed bcc structure (blue). Crystallographic different oriented grains are separated by grain boundaries (yellow). Depending on the shock strength the transformed region can be a mixed phase region and the resulting shock wave structure is a split two-wave structure consisting of an elastic precursor and a slower transformation wave. The initial nucleation takes place along the (bcc011) close-packed planes transforming into the close-packed planes of the close-packed material. The comparison of the nucleation process for three different shock strength (increasing from left to right in the movie) is shown in the last movie where only atoms with a lateral displacement larger than about 1/6 of the nearest neighbor distance are shown. The samples consist of aprox 8 million atoms (i.e. 40.2nm x 40.2nm x 57.4nm) and was simulated for 8.76ps.

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Tags:

• Shock
• induced
• structural
• phase
• transformation
• bcc
• iron

[jorgeralph]

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