Eutectoid transformation in Cu-Be alloys tuned by cooling pathways: from crystallography to mechanical properties

High-Be Cu-Be alloys exhibit dendritic segregation and brittle β/γ phases, which complicate processing and applications. This study investigates the influence of cooling path on eutectoid transformation, microstructure, and mechanical properties in Cu-2.8Be and Cu-3.8Be alloys. A two-step homogenization treatment effectively eliminates segregation and suppresses the formation of harmful acicular phases. Diffusion-kinetic and thermodynamic analyses demonstrate that both the initial temperature and cooling rate determine eutectoid morphology and extent. Crystallographic and Eshelby-based analyses reveal that the β → γ transformation involves an isotropic contraction of ~3.9%, producing much lower strain energy than the anisotropic β → α transformation (~28.5% expansion and ~9.2% contraction), thus explaining the preferential nucleation of γ. Rapid cooling promotes incomplete eutectoid decomposition along grain boundaries, forming fine α/γ lamellae with interlamellar spacing down to ~7 nm. Lattice strain analysis confirms considerable distortions at α/γ interfaces (εxxα=0.0167, εxxγ=0.0095). The mechanical incompatibility and high internal strain at these interfaces cause stress concentration and crack initiation. This work establishes a process-microstructure-property-mechanism framework essential for controlling the performance of high-Be Cu-Be alloys.