Abstract
CoSn 3 phase is formed in Sn/Co couples reacted at 200°C. The reaction phase shows a unique cruciform pattern that is observed for the first time in the solid/solid reaction. The reaction phase layers are thick and uniform along the edges of the Co substrate, and there are no reaction phases at the corners. A continuous reaction layer is formed in Sn/Co couples reacted at 180°C. A metastable CoSn 4 phase is formed at the corner, and the reaction phase along the edge of the Co substrate is the CoSn 3 phase. The reaction CoSn 3 phase region shows a cruciform pattern if the CoSn 4 phase region is ignored. It is concluded that the Sn flux is much faster than the Co flux, and the cruciform pattern of the reaction CoSn 3 phase layer is formed either by cracking or transformation to the CoSn 4 phase at the corners where stresses are most intensified. © 2007 Materials Research Society.