EFFECT OF DEFORMATION ON MIGRATION RATE OF GRAIN BOUNDARIES IN NICKEL

Abstract

Effect of deformation along various directions against migrating  boundary on migration rate of edge boundaries with <100> and <111>  misorientation  axes  in  nickel  was  studied  by  means  of  molecular  dynamics  method.  Grain  boundaries  were  created  in  U-shaped  model.  Force of boundary surface tension, arising from the boundary intension  to  minimize  its  energy,  was  the  reason  of  directed  movement  of  the  boundary toward its area decrease. The force provoking migration and  migration rate of the boundary remained constant throughout the entire  movement  of  the  boundary,  gradually  decreasing  towards  the  end  of  computer  experiment,  which  made  it  possible  to  measure  migration  rate quite simply. Effect of uniaxial deformation along the X, Y, Z axes  on migration rate of the boundaries was considered. Uniaxial deformation in the model was set at beginning of the computer experiment by  changing  corresponding  interatomic  distances  along  one  of  the  axes.  Interactions of nickel atoms with each other were described with the aid  of Cleri Rosato many-particle potential constructed in the framework  of  tight  binding  model.  For  the  boundaries  considered,  dependences  of  migration  rate  on  misorientation  angle  at  temperature  of  1700 K  were obtained. It is shown that the high-angle <111> and <100> edge  boundaries migrate approximately at the same rate, while mobility of  low-angle  boundaries  differs  significantly:  low-angle  <111>  boundaries migrate about twice as fast as the <100> boundaries. It was found  that in almost all cases, both at elastic compression and tension deformation, migration rate of considered boundaries was slowed down. An  exception was the case of deformation along the <111> edge boundary  axis. When compressing along the edge axis, <111> boundary migrated faster, while on the contrary, it was slower at tension. The obtained  results testify to the fact that migration of edge boundaries is not due to  diffusion processes, such as climbing of dislocations, single migrations of  atoms,  but,  apparently,  by  collective  atomic  permutations:  shifts, slides and splittings of grain boundary dislocations.