Micro- and nanostructural evolution of copper bronze CuAl10Ni5Fe5 during cooling from solution treatments

Abstract

The CuAl bronze alloy CuAl10Ni5Fe5 has been widely used in maritime components, such as large ship propellers, for many decades because of its excellent corrosion resistance and mechanical properties. The alloy is mainly manufactured by casting. In the present work, its micro- and nanostructural development during cooling from solution treatments is investigated. The cooling rates were varied over four orders of magnitude. The precipitation and transformation kinetics are examined in situ by differential scanning calorimetry. The differential scanning calorimetry cooling curves show a complex superposition of multiple reactions. The reactions cover a temperature range of about 800 K. To assign some distinct reactions to certain temperature ranges, a defined step quenching method has been applied. Extensive investigations on the resulting microstructure were performed by optical microscopy, scanning electron microscopy, and transmission electron microscopy. It is found that numerous structural features evolve during cooling (depending on the cooling rate), including formation of α-Cu grains, precipitation of several types of secondary κ-precipitates. The microstructural development of these κ_I, κ_II, and κ_III precipitates is more complex, as these particles are found to contain multiple types of tertiary phase particles. Tthe development of the microstructure is correlated with the resulting mechanical properties, in a way that the hardness is tested after cooling at different rates.