Morphological characteristics of multi-layer/substrate systems

Abstract

The analysed Al 3Ni 2–Al 3Ni multi-layer on a Ni-substrate was solidified in an apparatus for diffusion soldering under vacuum. The δ–ζ multi-layer on the (Γ1 + Fe)-substrate was solidified in an apparatus for hot dip galvanizing. Isothermal solidification was applied to produce both coatings. The devices constructed allowed the solidification process to be arrested after a predetermined time. The period of time from the beginning of solidification to the applied arrest was introduced into the definition of a back-diffusion parameter, α. The back-diffusion parameter was employed to work out a model for solute redistribution. Experimental solute redistribution resulted from undercooled peritectic reactions accompanying the solidification of a multi-layer on a given substrate. The Al-solute and Zn-solute redistributions after the back-diffusion occurring during solidification with the presence of undercooled peritectic reactions were measured to identify the phases appearing. A thermodynamic theorem of the maximum driving force was applied to determine the sequence of phase appearance in contact with the liquid. The experimental sequence of phases appearing was tested with the thermodynamic predictions. The model for solute redistribution was verified through a fitting of the theoretical solute redistribution profile with experimental data. These data were obtained by means of electron microscopy techniques in both the multi-layers coated onto metallic Ni and (Γ1 + Fe) substrates. The experimental sequences of the peritectic phases appearance in both multi-layers were also confirmed by the model of solute redistribution.