Phase diagram of the Cu–Ni3Al pseudo-binary system

Cu–Ni–Al alloys with a Ni to Al ratio of approximately 3.0 are of particular interest for the development of electrically conductive products; thus, investigating their phase behavior is essential for achieving specific properties in these materials. In this study, the phase diagram of the Cu–Ni3Al pseudo-binary system was experimentally determined using cast and fully heat-treated Cu–Ni3Al alloys with a wide range of compositions, via microstructural observation and different quantitative analyses. The Cu–Ni3Al system undergoes a eutectic reaction Liquid ↔ α-Cu solid solution (Cuss) with an FCC structure +γ′-Ni3Al with an ordered FCC L12 structure. As the combined Ni and Al (Ni3Al) content increased, the microstructure transitioned from a single α-Cuss phase to two eutectic phases (α-Cuss and γ′-Ni3Al), to a primary γ′-Ni3Al phase and two eutectic phases, and to a single γ′-Ni3Al phase. The solidus and liquidus temperatures increased with the (Ni+Al) content. The solid solubility of (Ni+Al) in the α-Cuss phase (C(Ni+Al)) could be described by an Arrhenius-type equation (ln C(Ni+Al) = 5.50 – 2637/T), indicating a significant temperature dependence. In contrast, the solubility of Cu in the γ′-Ni3Al phase did not significantly decrease with the temperature. The phase diagram of the Cu–Ni3Al system was constructed from these results. The phase diagram will be useful in the development of Cu–Ni–Al alloys with exceptional strength and electrical conductivity.