Irradiation-induced selective precipitation in Cu-Nb-W alloys: An approach towards coarsening resistance

A novel approach towards coarsening resistance in the precipitate- strengthened Cu-based alloys is proposed, taking advantage of selective precipitation during low-temperature ion irradiation. In the case of Cu-Nb-W, W precipitates during room temperature irradiation, forming highly ramified clusters. During subsequent thermal annealing of alloys with composition close to Cu₉₀Nb₉W₁, the more mobile Nb atoms precipitate out on the W clusters, creating a core-shell structure and adopting the Bain orientation relationship within the Cu matrix. This structure is extremely resistant to coarsening. Annealing at 650 °C for 1 h results in a precipitates size <4 nm in diameter, and annealing for an additional 9 h causes no additional growth, even though Nb is highly mobile at this temperature and would coarsen in the absence of W. We attribute the remarkable stability of this precipitate structure to the strong immiscibility of W in Cu and to the highly ramified precipitate structure that W acquires during low-temperature irradiation.