Relationship between microstructure and properties of high-strength Cu-Ti-Cr alloys during aging

Abstract

This study investigated the microstructure and precipitation sequence of the Cu-3Ti-1Cr (wt%) alloy using optical microscopy, transmission electron microscopy (TEM), and high-resolution TEM and studied its strengthening mechanism. The precipitation sequence of Cu-3Ti-1Cr aged at 500 °C was a supersaturated solid solution→spinodal decomposition→β'-Cu4Ti phase with a tetragonal structure. Additionally, the orientation relationship between the Cu matrix and coherent β'-Cu4Ti precipitates were [001]Cu//[001]β' and (100)Cu//(130)β' at the peak aging time. Upon extending the aging time, the growth rate of the β'-Cu4Ti precipitates followed the Ostwald ripening law. The Cr element mainly exists in the forms of a coarse Cr phase, a TiCr2 phase, and as nanoscale Cr precipitates in the matrix. This plays an important role in inhibiting discontinuous precipitation and ensuring the stability of properties. With an increase in the aging time, the hardness increased initially and then decreased slightly after 2 h, thereby indicating over-aging. Precipitation strengthening was the major factor contributing to the high strength of the Cu-3Ti-1Cr alloy.