Effect of Cu on the evolution of precipitation in an Fe–Cr–Ni–Al–Ti maraging steel

The evolution of precipitates in an Fe–Cr–Ni–Al–Ti stainless maraging steel alloyed with Cu was investigated during aging at 525 °C. Atom probe tomography was used to reveal the development of precipitates and to determine their chemical composition. Two types of precipitates were observed to form during the aging process. Based on their chemical composition these are assumed to be NiAl B2 and Ni3(Ti,Al) (η-phase). The two phases of precipitates were found to develop independently of each other and the addition of Cu was found to accelerate precipitation. However, the effect of Cu on the nucleation of these phases is different: on the one hand, in the case of NiAl, Cu is incorporated and thus reduces the activation energy by reducing the lattice misfit; on the other hand, Cu acts as a nucleation site for the precipitation of Ni3(Ti,Al) by forming independent Cu clusters.