Effect of heat treatment on corrosion behaviour of alloy 625 additively manufactured via wire-based methods

This study investigates how heat treatment affects the corrosion behaviour of alloy 625 produced by wire-based additive manufacturing, specifically laser-wire directed energy deposition (LW-DED) and wire arc additive manufacturing (WAAM). Rapid solidification in these processes leads to dendritic microstructures with elemental segregation and intermetallic phase formation, which impact corrosion resistance. LW-DED has a comparatively higher cooling rate than WAAM, resulting in finer microstructures and interdendritic regions. A solution heat treatment at 1038°C was applied to examine its influence on microstructure and corrosion properties. Electrochemical tests in 3.7% HCl assessed material performance and induced corrosion, while scanning electron microscopy and energy dispersive spectroscopy analyses characterised microstructural changes. Results show that heat treatment encourages recrystallisation and reduces elemental segregation, making the microstructure of LW-DED samples similar to conventional wrought material. WAAM samples, which presented coarser as-built microstructure and larger interdendritic regions, were impeded by a lower driving force for recrystallisation and additional barriers from Laves phase pinning. As a result, the WAAM samples displayed only partial recrystallisation and retained some dendritic features under the same heat-treatment conditions. These changes enhanced corrosion resistance, as demonstrated by lower corrosion current densities and higher corrosion potentials in heat-treated samples compared to as-built ones. Specifically, the average corrosion potential increased by 237 mV for LW-DED and 20 mV for WAAM, while average corrosion current density decreased by 28% and 45%, respectively, after heat treatment. The findings highlight the significance of optimising heat treatment with the manufacturing method to improve the corrosion resistance of additively manufactured superalloys for extreme environment applications.