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

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The coarsening behavior of rod-shaped and spherical δ-Ni 2Si 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 〈5̄58〉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. © 2011 Springer Science+Business Media, LLC.