Influence of cooling speed on the solidification of a hyper-eutectic Cu-Sn alloy

Cu[BOND]Sn alloys with a hyper-eutectic composition (97.53 at% Sn, 2.42 at% Cu and 0.05 at% impurities) were melted in a Bridgman-type furnace and cooled at different velocities ranging from free fall to 13 µm/s. The formation of the intermetallic phase along the alloys, as well as the size, distribution and microstructure were observed as a function of cooling speed, showing different particle morphologies and growth. The intermetallic phase formed was Cu6Sn5 as confirmed by chemical analysis and X-ray measurements. Electron backscattered diffraction (EBSD) measurements indicate that the η′-monoclinic phase of the Cu6Sn5 intermetallic was formed on all samples, together with the β-Sn. SEM images both transversal and longitudinal cross-sections of alloys cooled at different velocities.