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

摘要

Broad ranges of cooling rates (T) 0.8-30.5 and 0.4-5.0Ks(-1) are attained during directional solidification of eutectic Sn-0.2wt Ni and hypereutectic Sn-0.5wt 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 -Sn cells are associated with cooling rates >5.5 and >2.7Ks(-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.