Interface chemistry and bonding strength for diffusion-bonded Fe/Fe-FeO/Al₂O₃ systems

Abstract

The samples for this study were made by oxidizing the interface region of an Fe/Al₂O₃ system containing either wüstite or Fe-FeO composite (I) as interlayer. The bonded materials of Fe/FeO/Al₂O₃ and Fe/I/Al₂O₃ were prepared by hot-pressing. For analysis of the boundary region electron probe microanalysis (EPMA), transmission electron microscopy and X-ray diffraction were used; at the FeO/Al₂O₃ and I/Al₂O₃ interfaces a newly formed reaction layer of about 6 μm in thickness containing iron, aluminium and oxygen could be identified, but EPMA failed to reveal the Fe/FeO interface. Therefore, the interface of iron single crystals with FeO scale was investigated by Auger electron spectroscopy and X-ray photoelectron spectroscopy, and at the Fe/FeO interface formation of a transition layer with a thickness of several hundred nanometres was observed. Through the Fe/I interface, interdiffusion of iron occured. Fe/I/Fe and Al₂O₃/l/Al₂O₃ bonded materials had tensile strengths of 150 and 130 MPa, respectively, when an interlayer of Fe-25 mol% FeO was applied between both bonding pairs.