Coarsening of Decomposed Phases in Cu-Ni-Cr Alloys

The coarsening process of the decomposed phases was studied in the Cu-34wt.%Ni-4wt.%Cr and Cu-45wt.%Ni-10wt.%Cr alloys aged at 600, 700 and 800 °C for different times by transmission electron microscopy. The morphology of the coherent decomposed Ni-rich phase changed from cuboids to platelets aligned in the <100= Cu-rich matrix directions as aging progressed. The variation of mean equivalent radius of the coherent decomposed phases with aging time followed the modified LSW theory for thermally activated growth in ternary alloy systems. The linear variation of the density number of precipitates and matrix supersaturation with aging time, also confirmed that the coarsening process followed the modified LSW theory in both alloys. The size distributions of precipitates in the Cu-Ni-Cr alloys were broader and more symmetric than that predicted by the LSW theory. The coarsening rate was faster in the symmetrical Cu- 45wt.%Ni-10wt.%Cr alloy due to its higher volume fraction of precipitates.