First-principles study of phase transformations in Cu–Cr alloys

Abstract

The average energy per atom, the formation energies, and the cohesive energies of Cu–Cr–X (X˭Zr, Ag, and In) phases with body-centered cubic (BCC) or face-centered cubic (FCC) structures were calculated using the first-principles method. The phase transformation sequence in the Cu–Cr binary alloy and the distributions of Zr, Ag, and In atoms in CuCrX precipitates were also studied. FCC atomic clusters are formed in the Cu–Cr binary alloy at the beginning of aging, and then transformed into a metastable FCC Cu–Cr phase during aging. When the Cr concentration of the precipitates increases to 60 at%, the formation and cohesive energies of the BCC Cu–Cr phase become less than those of the FCC Cu–Cr phase. This indicates that the BCC Cu–Cr phase is more stable than the FCC structure. In Cu–Cr–X (X˭Zr, Ag and In) ternary alloys, Zr atoms are mainly distributed in the periphery of FCC CuCrZr precipitates, while Ag atoms are randomly distributed in FCC CuCrAg precipitates, which is consistent with experimental results. High-resolution transmission electron microscopy and atom probe tomography indicate that In atoms are randomly distributed in the CuCrIn precipitates of the under-aged Cu–Cr–In alloy. This is consistent with our first-principles calculations.