Phase transformations and metastable states in a Cu-20 m.% Sn alloy: An integrated HEXRD, TEM, and APT investigation

This study explores the phase transformations and metastable states in a Cu-20 m.% Sn alloy, focusing on both stable and martensitic phases. High-energy X-ray diffraction (HEXRD) analyses revealed a metastable phase range between 200°C and 375°C. Identifying phases within this range was challenging due to the incomplete crystallographic descriptions of reported phases in the literature. Correlative transmission electron microscopy analysis identified three different phases, assigning α′ and β phases with certainty and tentatively designating a third phase as β ₁′′. Further confirmation using HEXRD was inconclusive due to the limited available data on the structure of β ₁′′. Atom probe tomography supported the presence of β ₁′′ by revealing distinct chemical regions, correlating the α′ and β ₁′′ phases, and indicating coupled growth as lamellar precipitates. Despite limited descriptions of β ₁′′, additional HEXRD investigations suggested its metastability. Martensitic transformation conditions were analyzed, showing that the α′ + β ₁′′ phases can be induced through aging, contrary to existing literature. Comparative diffractogram analysis, including a direct comparison of the metastable phases with the diffractogram of a cymbal – known for its exceptional acoustic properties – suggests that the α′ + β ₁′′ phases could similarly enhance acoustic performance, expanding the understanding and potential applications of Cu-Sn alloys.