Microstructural Analysis of Cu-Ti Alloys Micro-Alloyed with Al and Fe Using Replica Method

Age–hardenable Cu–Ti alloys, which combine high strength and high electrical conductivity, are widely used as conductive materials and have attracted significant interest due to the miniaturization and performance enhancement of electronic devices. The addition of trace amounts of third elements, such as Al and Fe, has been found to effectively improve alloy properties. However, accurately evaluating the effects of these minor additions remains challenging. In this study, a detailed microstructural analysis of fine precipitates and secondary phases in Cu–Ti alloys with trace additions of Al and Fe was conducted using TEM observation with replica specimens. In a Cu–3.2Ti–1.1Al–0.1Fe (mass%) alloy, solid–solution treatment resulted in the formation of Cu3Ti2 with a tetragonal, 50–100 nm in size, incorporating approximately 11 at% Fe. After subsequent aging treatment, a metastable β′–Cu4Ti (tetragonal) phase was observed within the Cu matrix grains, similar to conventional Cu–Ti alloys. However, unlike in binary Cu–Ti alloys, a lamellar structure containing β–Cu4Ti did not form at the grain boundaries; instead, Cu2TiAl (cubic) precipitates, 0.5–1 µm in size, were identified. These findings demonstrate that the replica method is a highly effective technique for the precise analysis of the composition and structure of fine precipitates in Cu–Ti alloys. The results provide valuable insights for optimizing the microstructure of Cu–Ti alloys and advancing their material design.