TEXTURAL CHANGES DURING GRAIN-GROWTH OF RECRYSTALLIZED PURE NICKEL AND A FEW NICKEL-COBALT ALLOYS

The present study deals with the textural changes during grain growth of recrystallized pure nickel and five nickel-cobalt alloys (Co rangin g between 10 and 60 mass%). At the beginning of the grain growth stage , the volume fraction of the cube texture component was observed to be maximum in the case of pure nickel. This gradually decreased with inc reasing the cobalt content of the alloy, finally disappearing complete ly in the Ni-60 Co alloy. The lowering of the grain growth exponent wi th increasing cobalt content was small but significant, and the activa tion energy of grain growth increased step-wise both by increasing the annealing temperature and the cobalt content. At the initial stages o f grain growth, the process could be dominated by the migration of hig h mobility special boundaries, giving rise to lower values of activati on energies. The principal texture component at this stage appeared to be the cube. In later stages, due to the non-availability of special boundaries, the process was dominated by the migration of less mobile random boundaries and the corresponding activation energy values were relatively high. The cube texture was also replaced by other texture c omponents. In the Ni-Co alloys, the availability of cube oriented grai ns, at the beginning of the grain growth process, decreased progressiv ely with increasing the cobalt content. This, coupled with the effect of the solute Co atoms in locking the advancing grain boundaries, appe ars to be responsible for the higher values of the activation energy i n the alloys.