Coarsening of δ-Ni2Si precipitates in a Cu-Ni-Si alloy

The coarsening behavior of rod-shaped and spherical delta-Ni2Si precipitates in a Cu-1.86 wt% Ni-0.45 wt% Si alloy during aging at 823-948 K has been investigated by measuring both precipitate size by transmission electron microscopy (TEM) and solute concentration in the Cu matrix by electrical resistivity. The rod-shaped delta precipitates have an elongated shape along aOE (c)>(m) and a {110}(m) habit-plane facet. The coarsening theory of a spherical precipitate in a ternary alloy developed by Kuehmann and Voorhees (KV) has been modified to a case of rod-shaped precipitates. The coarsening kinetics of average size of the rod-shaped and spherical delta precipitates with aging time t obey the t (1/3) time law, as predicted by the modified KV theory. The kinetics of depletion of the supersaturation with t are coincident with the predicted t (-1/3) time law. Application of the modified KV theory has enabled calculation of the energies of sphere, {110}(m) and rod-end interfaces from the data on coarsening alone. The energy of the {110}(m) interface having a high degree of coherency to the Cu matrix is estimated to be 0.4 J m(-2), the incoherent sphere-interface energy 0.6 J m(-2), and the rod-end interface energy 5.2 J m(-2).