MICROSTRUCTURE AND STRENGTH OF NANOCRYSTALLINE COPPER ALLOY PREPARED BY MECHANICAL ALLOYING

Polycrystalline materials having an ultrafine grain size may be prepared by mechanical alloying. Such a material has been prepared here with a copper matrix and a uniform dispersion of particles which stabilises the fine microstructure. It is shown that the grain size of the copper matrix may be explained in terms of the conventional models of boundary pinning by particles, even for grain sizes below 40 nm. For grain sizes larger than about 100 nm, material strength may be explained by dislocation-particle interactions as illustrated by TEM observations. For grain sizes below this limit, however, strengthening is not as great as dislocation theory would predict based on the distribution of particles in the material; in addition TEM observations show no indication of the presence of dislocations. A different deformation mechanism seems to control strengthening for these materials of nano-scale grain size.