Nanocrystallization and Amorphization Mechanisms in Zr-X Alloys during the ARB Process

The gradual nanocrystallization and amorphization mechanisms in various Zr-X alloys during accumulative roll bonding (ARB) are explored. The effects of strain accumulation, the relative initial hardness of the elemental foils, the enhanced diffusion, and the critical nano size for the sudden transformation from the nanocrystalline phase to the amorphous state are examined. For elemental foils with compatible initial hardness, the nanocrystallization and amorphization rates appear to be higher. The estimated diffusion rates during ARB are higher by several orders of magnitude than the lattice diffusion in bulk materials. When the nano grains are refined down to around 3 nm, sudden transformation into the amorphous phase would occur.