Microstructure Characteristic and Evolution Mechanism of Cu–Ni–P Alloys under Different Cooling Rate

The microstructure characteristics at different cooling rates and phase extraction treatments of Cu–34.1Ni–4.5P ingots were discussed in this paper. It was found that Cu–34.1Ni–4.5P ingots were composed of Cu and multiple Ni–P phases, including NiP, Ni 5 P 2 , Ni 5 P 4 and Ni 12 P 5 . With the cooling rates decreasing from 1710 to 52 K/s, the growth of Ni–P dendrites during the solidification process would be gradually taken place, resulting in the coarsening of Ni–P phases to some extent. It was observed that the average ligament width of Ni–P grains was 1.64 μm with cooling rates as 1710 K/s which was 33% lower than 52 K/s, meaning that the lamellar spacings would also been significantly decreased with the increase of solidification rates. Furthermore, a bulk self-supporting porous Ni–P skeleton materials with hierarchical structure were obtained by dealloying of Cu–34.1Ni–4.5P precursor alloys. Meanwhile, the corresponding mechanism for the formation of Ni–P with skeleton structure was also disscussed.