Experimental Determination of Phase Diagram for Cu–Ni₃Al Pseudo–Binary System

Abstract

The phase diagram of Cu–Ni₃Al pseudo–binary system was experimentally determined using fully heat–treated Cu–(26.7 to 94) at.％ Ni₃Al alloys, via microstructural observation and quantitative analysis such as TEM–EDS, DSC, and electrical resistivity measurements. The Cu–Ni₃Al pseudo–binary system exhibited a eutectic–type phase diagram with a three–phase coexistence region of Liq. + γ–Cu solid solution (Cu_ss) + γ’–Ni₃Al. As the (Ni+Al) content in the Cu–Ni₃Al alloys increased, the microstructure transited in the order of γ single–phase, eutectic (γ+γ’) two phases, primary γ’ + eutectic (γ+γ’) phases, and γ’ single phase. The melting start and end points of Cu–Ni₃Al alloys monotonically increased from 1084°C to 1380°C with increasing the (Ni+Al) content. The solid solubility of (Ni+Al) content in the γ phase C_(Ni+Al) could be described by the Arrhenius–type equation of ln C_(Ni+Al) = 5.50–2637/T, (T：absolute temperature), which indicated that the γ single–phase region had a relatively large temperature–dependence. Whereas, the maximum solubility of Cu in γ’ phase was approximately 14 at. ％, which was not significantly decreased with the temperature decreased.