Presence of retained crystalline seed necessary for bicrystal-liquid-bicrystal phase transformation

Regaining of the original bicrystal structure during solidification after melting is found to be possible only if a fraction of crystalline seed is retained in the melt as per this molecular dynamics study. The effect of cooling rate on retaining the crystalline seed is also investigated. The bicrystal specimen is heated up to 1850 K with a constant heating rate of 3.5 K ps−1 and instantly cooled with different cooling rates i.e. 1 K ps−1, 5 K ps−1, 10 K ps−1, 15 K ps−1 and 20 K ps−1. It has been observed through total energy analysis that specimen cooled with 1 K ps−1 cooling rate dissipates the energy throughout the specimen causing randomization of atoms resulting into disappearance of the crystalline seed and formation of nanocrystalline structure. Whereas comparatively higher cooling rates does not allow complete dissipation of energy and retain the crystalline seed thus transform into bicrystal. It has been found through Voronoi polyhedra analysis that during slower cooling rate, icosahedral clusters are formed which play a vital role in formation of nanocrystalline structure.