Study by DSC and HRTEM of the aging strengthening of Cu-Ni-Zn-Al alloys

Abstract

The structural changes of a Cu-12 wt.% Ni-17 wt.% Zn-1.7 wt% Al alloy as a function of the aging temperature have been studied by means of Differential Scanning Calorimetry (DSC), high resolution transmission electron microscopy (HRTEM) and hardness measurements. It has been proposed a hardening mechanism that implies the crystallization of a Ll(0) Cu2NiZn phase coherent with the matrix a phase followed, firstly, by its transformation into a Ll(2) coherent phase and, secondly, by the precipitation of this phase. It has been shown that aluminum play an important role in the precipitation hardening process because Cu2NiZn precipitates are not formed by aging a ternary Cu-Ni-Zn alloy of similar composition. It has been shown by the first time that DSC could be a powerful tool for discriminating the whole set of phase transformations undergone by alloys as a function of the annealing temperature from a single heating run.