Non-isothermal kinetics and the effects of alloying elements on bainite precipitation in the Cu74.5Al15.0Mn10.5 alloy

Abstract

In as-quenched CuAlMn-based alloys, the bainitic precipitation can occur between 450 and 625 K on heating. This reaction can promote diffusion into the martensitic phase and can damage the shape memory effect. In this study, the effect of the fourth alloying element (Ag, Ga, and Gd) on bainitic precipitation kinetics in the Cu74.5Al15.0Mn10.5 alloy was evaluated using differential scanning calorimetry, optical microscopy, X-ray diffraction, and the non-isothermal isoconversional method. The study of the Gd addition to the Cu74.5Al15.0Mn10.5 alloy indicated that the Cu5Gd phase increased the number of nucleation sites, thereby reducing the average isoconversional activation energy for the bainitic reaction. Nonetheless, the Ag and Ga additions promoted a more effective change in the kinetic mechanism of the bainitic precipitation. The Ga addition reduced the isoconversional activation energy value and induced the bainitic phase formation at lower temperatures, but it also introduced parallel reactions that turned their lateral growing slower. On another hand, Ag elevated the initial isoconversional activation energy value and shifted up the bainitic precipitation starting, but the presence of Ag precipitates induced the bainite formation in a narrower temperature range. Therefore, the additions of Ag, Ga, and Gd to the Cu74.2Al15.0Mn10.5 alloy changed bainitic precipitation kinetics, which can be associated with modifications in the Cu diffusion energy and the number of nucleation points.