The intergranular precipitation behavior of G phase in a high-performance complex cast Cu-Ni-Al alloy

G phase has been widely investigated and used in ferritic and austenitic steels, while relatively less attention is paid to its formation in copper alloys. This study focuses on the precipitation behavior of G phase along the grain boundary in a cast Cu-17Ni-3Al based complex alloy by using multiscale characterization techniques and firstprinciples calculations. The results reveal that these intergranular G phases have a composition close to ideal Ni16Ti6Si7 but incorporating Zr and minor Cr. They tend to precipitate at the high-angle grain boundaries (excluding CSL boundaries) adjacent to the intergranular oxides and hold rational orientation relationship with only one side of Cu matrix. The replacement of Ti by Zr in G phase is energetically favourable with respect to the formation energy, and meanwhile, it decreases the lattice misfit of the G phase/matrix interface, thereby favouring the substitution of Ti when compared with other G phase formers.

Automated summary

This study investigates the precipitation behavior of intergranular G phase in a cast Cu-17Ni-3Al based complex alloy. The results show that the G phases have a composition close to Ni16Ti6Si7 but with the incorporation of Zr and minor Cr. They tend to precipitate at high-angle grain boundaries adjacent to intergranular oxides and hold a rational orientation relationship with the Cu matrix. The substitution of Ti by Zr in G phase is energetically favorable, reducing the lattice misfit of the G phase/matrix interface.