Interfacial Reactions in Sn/Ni-xW Couples

Solid/solid and liquid/solid reaction couple techniques were applied to investigate the interfacial reactions in the Sn/Ni-xW systems (x = 0 wt.%, 1.0 wt.%, 5.0 wt.%, and 7.5 wt.%) at 160A degrees C to 300A degrees C for various reaction times. The results indicate that only the Ni3Sn4 phase was formed in the Sn/Ni-1 wt.%W couple. The Ni3Sn4 phase and ternary Ni37-42Sn48W10-15 phase (T-1) were formed at the Sn/Ni-5 wt.%W interface. After 400 h of aging at 210A degrees C, the Ni26-31Sn59W10-15 phase (T-2) with a discontinuous layered structure was formed in the Ni3Sn4 layer. The results in the Sn/Ni-7.5 wt.%W couple were similar to those in the Sn/Ni-5W couple. A multilayer structure, T-1/Ni3Sn4/T-2/Ni3Sn4, was formed after 100 h of aging at 210A degrees C. When the reaction temperature was increased to 225A degrees C, a new ternary phase composed of Ni5-15Sn50W35-45 (T-3) was formed. T-1, T-2, and T-3 phases were likely to be metastable phases with an amorphous structure composed of nanocrystal grains. The liquid/solid-state interfacial reactions in the Sn/Ni-xW couples are different from those in the solid-state reactions. The T-1 phase was formed between the Ni3Sn4 phase and Ni-xW alloys when the W content was greater than 5 wt.%. According to the transmission electron microscopy analysis results the T-1, T-2, and T-3 phases were likely to be metastable phases with an amorphous structure composed of nanocrystal grains.