The phase transformation and its effects on properties of a Cu-0.12 wt% Zr alloy

The phase transformation of a Cu-0.12 wt% Zr alloy during the aging process at 450 degrees C was investigated by Transmission electron microscopy (TEM) and high-resolution transmission microscopy (HRTEM) in the study. The strengthening mechanism was studied as well. The precipitation sequence of Cu-0.12 wt % Zr aged at 450 degrees C is supersaturated solid solution -> Zr-rich atomic clusters -> semi-coherent Cu5Zr phase. This transformation can be achieved by the accumulation of Zr-atom layers. The Zr-rich atomic clusters are composed of disk-shaped monolayers of Zr atoms. The Cu5Zr phase precipitate out in the nucleation of Zr-rich atomic clusters. The disc-like Cu5Zr phases with face-centered cubic structure are found in the matrix, whose habit plane is parallel to {111}(Cu) plane. The orientation relationship with [112](Cu) parallel to [011](Cu5Zr), (11 (1) over bar)(Cu) parallel to (11 (1) over bar)(Cu5Zr) exists between the Cu and Cu5Zr phases. The space structure model of Cu5Zr phase can be established. With aging time, the hardness increases continuously first, and decreases slightly after 8 h, indicating overaging. The strengthening effect of Cu5Zr phase precipitated in aging at 450 degrees C for 8 h is calculated to be 5.8 MPa according to the Orowan strengthing, which is quite consistent with the experimental data. (C) 2015 Elsevier B.V. All rights reserved.