Highly efficient energy and mass transfer in bcc metals by supersonic 2-crowdions

During irradiation, bombardment with energetic particles, or plasma treatment, structural transformations occur in materials, in which point defects play a very important role. Highly mobile crowdions contribute to the transfer of mass and energy in the crystal lattice. Static and slowly moving crowdions are well studied, in contrast to crowdions moving at a speed exceeding the speed of sound. Here, for the first time, dynamics of supersonic N-crowdions (N=1,2) is investigated in bcc metals (tungsten and vanadium) with the help of molecular dynamics simulations. N-crowdions are excited by imparting sufficiently high initial velocities to N neighboring atoms located in the same close-packed atomic row along this row. Both supersonic 1- and 2-crowdions carry one interstitial atom each. Modeling shows that much less energy is required to excite a 2-crowdion compared to a 1-crowdion. Energy dissipation for a 2-crowdion is much slower than for a 1-crowdion suggesting that the supersonic 2-crowdion is an efficient mass transfer mechanism in bcc metals. The distance traveled by supersonic 1- and 2-crowdions in W is much greater than that in V. The supersonic crowdion in W transforms into a moving subsonic crowdion, and in V it transforms into a standing subsonic crowdion carrying a localized high-amplitude oscillation mode. These differences can be explained by the features of interatomic interactions in W and V.