Reactive phase formation and isothermal solidification in the Ni/Au-18.6Si/Ni layer system

In the present work, the isothermal solidification behavior in the Ni/Au18.6Si/Ni (at.%) system was analyzed by means of microstructure evolution and time to complete solidification. Since phase diagram information for the Au-Ni-Si ternary system is scarce, some phase equilibria in the Au-Ni-Si ternary system at 320 °C and 500 °C were characterized. In additional annealing experiments the early and intermediate stages of the reaction (<108 min over liquidus temperature) were investigated. The formation of the Ni-Si intermetallics (Ni3Si, NiSi) could be followed and the probable solidification mechanism was be derived. Cyclic differential scanning calorimetry (DSC) measurements were applied to estimate the time to complete solidification and to calculate the concentration change in the joint gap over time. In comparison with our previous work on the Ni/Au28Ge/Ni (at.%) solidification took much longer when Au18.6Si (at.%) interlayers with the same thickness were used. This was partially attributed to different growth kinetics of the Ni-Si IMCs, but also to the potential formation of a thin SiO2 layer on the Au-Si foil surface during the DSC tests.