Grain boundary structure of ultrafine grained pure copper fabricated by accumulative roll bonding

Grain boundary structures of ultrafine grained pure copper (Cu) fabricated by the accumulative roll bonding (ARB) have been studied. The atomic structures of grain boundaries in the ARB processed Cu (ARB-Cu) were observed by high resolution electron microscopy. In order to compare the grain boundaries in the ARB-Cu with equilibrium grain boundaries, the grain boundary energy and structure of symmetric tilt boundaries with (110) common axis in pure Cu were computed by molecular dynamics simulation (MD). The low angle boundaries in the ARBCu were basically described by conventional dislocation model and simultaneously there were some local structures having certainly high energy configurations. The grain boundaries with large misorientation in the ARB-Cu are basically described by the structural units predicted for the normal grain boundaries by MD. The present results indicate that the atomic structures of the boundaries in the Cu severely deformed by theARB are rather similar to those of the equilibrium grain boundaries, except for the local distortions.