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

The coarsening behavior of rod-shaped and spherical δ-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 δ precipitates have an elongated shape along 〈\( \overline{5} 5 8 \)〉_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 δ 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.