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Characterization of the isothermal solidification process in the Ni/Au–Ge layer system

Weyrich, Nico, Leinenbach, Christian
Journal of materials science 2015 v.50 no.10 pp. 3835-3844
alloys, annealing, coatings, differential scanning calorimetry, germanium, gold, microstructure, nickel, solidification, temperature
The eutectic Au28Ge (at.%) solder alloy in combination with Ni substrates or Ni coatings is interesting for applications in transient liquid phase (TLP) bonding. To achieve sound joints with high re-melting temperatures, it is necessary to gain profound knowledge about the joining process. In this work, the isothermal solidification behavior in the Ni–Au28Ge (at.%) system was analyzed by means of microstructure evolution and time to complete solidification. In short-time annealing experiments the early stage of the reaction (<300 s over liquidus temperature) was investigated. It was observed that a continuous layer of Ni₅Ge₃forms at the substrate–solder interface before scallop-like NiGe grains start to grow as solidification proceeds. Cyclic differential scanning calorimetry measurements were applied to estimate the time to complete solidification. Solidification was completed after less than 1 h in the Ni–Au28Ge (at.%) system, which enables comparably short processing times for TLP bonding.