High Cooling Rate, Regular and Plate Like Cells in Sn–Ni Solder Alloys

Abstract

Broad ranges of cooling rates () 0.8–30.5 and 0.4–5.0 K s−1 are attained during directional solidification of eutectic Sn–0.2 wt% Ni and hypereutectic Sn–0.5 wt% Ni alloys, respectively. A reverse high cooling rate cell‐to‐dendrite transition occurs for the eutectic composition and a transition from high cooling rate cells to plate like cells for the hypereutectic alloy. High cooling rate β‐Sn cells are associated with cooling rates >5.5 and >2.7 K s−1 for eutectic and hypereutectic compositions, respectively. A processing diagram, relating the ‘–Ni content’ space with the microstructural morphology, is proposed. A combination of plate like cells and plate NiSn4 eutectic phase results in higher ductility.