Electron Microscopy Investigations of Nanometer Thick Crystalline and Amorphous
Equilibrium Films at Metal-Ceramic Interfaces
Wayne D. Kaplan
Department of Materials Engineering
Technion - Israel Institute of Technology
Haifa 32000 Israel
The classical approach to the analysis of metal-ceramic joins is via wetting and the thermodynamic
work of adhesion. Contact angles derived from wetting experiments are a direct route to obtain
information on the energy of interfaces. However, the factors involved in wetting experiments
extend well beyond the contact angle as a function of temperature. These additional parameters
include the segregation of dopants and/or impurities in the metal and ceramic, the partial pressure
of reactive gases in the gas phase, and structural transformations at all three of the interfaces
involved in the wetting experiment. Two examples of the influence of these parameters will be
presented.
Impurities segregating to the metal-ceramic interface can significantly change the contact angle and
the thermodynamic work of adhesion. Equilibrium segregation can occur, in which the interface
energy is reduced due the presence of the segregant. In addition, non-equilibrium segregation can
lead to reconstruction of the interface structure. An example is the Ca doped Al-Al2O3 interface.
In this system a crystalline interfacial film results from non-equilibrium segregation, and wetting
experiments have shown that this film affects the contact angle and work of adhesion.
The second example which will be presented is the Cu-Al2O3system. The microstructure of
Cu/Al2O3 composites prepared by melt-infiltration of liquid copper into porous alumina preforms
was studied in detail by various transmission electron microscopy techniques. An amorphous glass
phase containing Si and Ca was found at Al2O3/Cu/Al2O3 triple junctions. A glass phase
containing Si and Ca is also present at Cu/Al2O3 interfaces, while Al2O3 boundaries remain dry.
Detailed high resolution transmission electron microscopy investigations show that the interfacial
glass phase at the Cu/Al2O3 interfaces exhibits a uniform equilibrium film thickness along the
interface region. While equilibrium amorphous films are known to exist at grain boundaries in
ceramics, to the best of the author’s knowledge this is the first time such a film has been found at a
metal-ceramic interface. The thickness of the interfacial film depends on long-range interatomic
forces. The physical significance of equilibrium amorphous films at metal-ceramic interfaces will
discussed.