RELATIONSHIP BETWEEN NANOCRYSTALLINE AND AMORPHOUS MICROSTRUCTURES BYMOLECULAR-DYNAMICS SIMULATION

A recently developed molecular-dynamics simulation method for the grow th of fully dense nanocrystalline materials by crystallization from th e melt was used together with the Stillinger-Weber three-body potentia l to synthesize nanocrystalline silicon with a grain size up to 75 Ang strom. The structures of the highly-constrained grain boundaries (GBs) , triple lines and point grain junctions were found to be highly disor dered and similar to the structure of amorphous silicon. These and our earlier results for fcc metals suggest that a nanocrystalline microst ructure may be viewed as a two-phase system, namely an ordered crystal line phase in the grain interiors connected by an amorphous, intergran ular, glue-like phase. The analysis of the structures of bicrystalline GBs in the same materials reveals the presence of an amorphous interg ranular equilibrium phase only in the high-energy but not the low-ener gy GBs, suggesting that only high-energy boundaries are present in nan ocrystalline microstructures. (C) 1997 Acta Metallurgica Inc.