Solid state bonding of Al2O3 with Cu, Ni and Fe: characteristics and properties

A solid state bonding technique under hot pressing was used for joining alumina with thin metal sheets of Ni, Cu and Fe. The microstructure and microchemistry of the ceramic-metal interface and of the fracture interface were examined using scanning electron microscopy (SEM) energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), in order to identify the adhesion mechanisms and the nature of strength limiting flaws. Interaction between the selected metals and alumina can be physical or physico-chemical in nature: very low amounts of interfacial compounds were formed, depending on the processing conditions and on the presence of oxygen in the system. Fracture and toughness tests indicated that high ceramic-metal interface strengths (up to 177 MPa) were achieved under the adopted processing conditions and that strength and toughness were directly related. Moreover, an increase in hardening in the metal interlayer at a distance of 2-3 mu m from the interface was observed in the samples with high strength values. The mechanical behaviour was related to several factors that strongly depend on the bonding conditions: plastic deformation of the metal, metal creep, metal intrusion and diffusion into alumina, and chemical reactions at the interface.