The phase transformation and strengthening of a Cu-0.71 wt% Cr alloy

Abstract

Abstract The phase transformation of a Cu-0.71 wt% Cr alloy during the aging process at 450 °C was investigated by Transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HRTEM) in the study. The strengthening mechanism was studied as well. The precipitation sequence of Cu-0.71 wt% Cr aged at 450 °C is supersaturated solid sloution→G.P zones (fcc Cr-rich phase)→fcc Cr phase→order fcc Cr phase→bcc Cr phase. This transformation can be achieved by the nucleation of coherent fcc spherical precipitates and growth and transformation of fcc precipitates into the bcc structure. When the specimen is aged aging for 1 h–24 h, both fcc and bcc precipitates exist in the matrix simultaneously. Ordering process is found during the aging process, which is in favor of the precipitation of Cr-rich phases. The orientation relationship between bcc Cr precipitates and the matrix exhibit NW-OR. The peak strength effect occurs after aging for about 8 h and the strength continues to decrease with prolonging aging time, indicating overaging. The strengthening effect of Cr-rich phase precipitated in aging at 450 °C for 8 h is calculated to be 146 MPa on the basic of the Orowan strengthening mechanism, which is in quite accordance with the experimental data (144.5 MPa).