Microstructure, precipitation behavior, and properties of quaternary Cu–Be–Co–Ni alloy under electromagnetic levitation

Electromagnetic levitation (EML) can provide a containerless environment and, consequently, large undercooling solidification for various metals. In this study, the microstructures, precipitated phase characteristics, properties, and strengthening mechanisms of Cu–0.2Be–1.6Co–1.6Ni alloy with different undercooling conditions were investigated using the EML method. The achieved undercooling range was 76–315 K. The microstructure of the alloy was mainly composed of dendrites and slender-strip precipitates. Under EML, the length and width of the precipitates decreased by an order of magnitude with increasing undercooling. The precipitates transformed from a α(Co) phase with a face-centered cubic structure to a metastable γ′ phase with a body-centered tetragonal structure. The microhardness increased almost linearly from 120 to 154 HV with enhanced undercooling. The electrical conductivity was higher than that of the master alloy and increased slightly with enhanced undercooling. Quantitative analyses of the strengthening mechanisms revealed the vital roles of solution and precipitation strengthening in the mechanical properties of EML alloys, whereby the former was weakened and the latter was strengthened as undercooling progressed. The simultaneous enhancement of the mechanical and electrical properties of Cu–0.2Be–1.6Co–1.6Ni alloy can be attributed to the increased solute precipitation and refined precipitates due to deep undercooling.