Changes in the phase composition and structure of electrodeposited tin-cobalt (Sn-Co) alloy layers (5-10 ??m) containing a limited quantity of Co (0.24, 2.4, 11.0, 17.0 or 26.5. wt.%) were studied using X-ray diffraction (XRD) and optical microscopy.The phase composition and coating structures of Sn-Co alloys in Sn-Co/Cu layers underwent considerable changes upon heating at 170??C for 100-200h and at 170??C for 200h followed by 205??C for 20h. The changes were dependent on the Co content in the alloy and the heating temperature. When examining the sample containing 11.0wt.% cobalt, an unidentified phase containing a Sn-Co compound, CoSn2 and CoSn3 formed upon heating at 170??C for 100, 140 and 200h. The structure of the layer surface was composed of spherical crystallites. The formation of the unidentified phase possibly caused the formation of needle-shaped crystals in the structure consisting of spherical crystallites. When the Co content of the Sn-Co layer was increased to 17.0-26.5wt.% and the sample was heated to 170??C for 100-200h, phases of CoSn, CoSn2, Co3Sn2 and CoSn3 were formed. The coating maintained its structure and was composed of spherical crystallites.In the Sn-Co/Cu system of layers containing 11.0, 17.0 or 26.5wt.% Co, Sn-Cu intermetallic compounds (Cu6Sn5 and Cu3Sn) did not form after heating at 170??C for 200h followed by 205??C for 20h. ?? 2010.
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