Abstract
The structure and energies of point defects and their clusters in metals have been studied because of their importance in nuclear technology. These studies are based on interatomic potentials. An interatomic potential for nickel has been developed using computer graphic facilities. The computer simulation of defects was carried out on an IBM 360/195 computer. The possible close-packed crystallographically distinct configurations of vacancy and solute clusters , in square lattices and face centred cubic crystals , have been enumerated. The transformations, growth and contraction mechanisms of these clusters have been given in terms of matrices. The unrelaxed energies of their formation have been tabulated using a Lennard-Jones potential. In order to find the energies of vacancy solute clusters another potential i.e. a vacancy-solute potential was required. This was achieved by introducing a factor f to the parent-parent potential. A range of values of f was used and it was found that f = 1/2 gives particularly interesting results. The interaction energies between vacancies and solutes were computed using a short ranged , central , non-equilibrium potential representing copper. These energies were very small but comparable to those available in the literature. The frequencies of different jumps were calculated and significiant differences discovered. It was found that most frequently the solutes interchange with vacancies. Also jumps leading to dissociation of the clusters have low frequencies. Computer simulation of the growth of vacancy clusters was also carried out using the same copper potential. As the stacking fault energy of copper is very low , these computer experiments predicted the growth of stacking fault tetrahedra. At the same time some metastable voids were also seen. As the stacking fault energy is a parameter of the potential , we decided to develop another potential for nickel which has a high stacking fault energy. The results with this new potential have demonstrated the effect of the change of this parameter. Investigations of discrete structures of grain boundaries and their interactions with point defects have produced some interesting results. In some cases the migration of vacancies become easier in the twinned crystals as compared to that in single crystals. These results are of particular interest to materials scientists as conventional experimental and theoretical techniques are not able to predict reliable information on these defects of atomic dimensions which control many physical and mechanical properties.