TEM investigation of reaction zone products formed between molten Al and CoO monocrystalline substrate

Summary

The research was aimed at microstructure characterization of the reaction products formed between molten aluminium and CoO single crystal during a sessile drop wettability test performed in vacuum at 700 and 1000°C for 120 min using contact heating procedure. The solidified Al/CoO couples were sectioned and used for cutting thin foils with focused ion beam. The transmission electron microscopy and energy dispersive X-ray spectroscopy were used for microstructure and local chemical analysis. The interaction of molten aluminium with CoO substrate at 700°C caused the formation of a corrugated 10–40 μm thick reaction zone (RZ). It consisted of aluminium matrix and Al₂O₃ crystallites varying in size, i.e. of ∼0.2 μm near the Al drop/RZ interface, growing up to 1–2 μm at the RZ centre and very fine nano-crystallites near the RZ/CoO interface. The reaction of aluminium with CoO at 1000°C produced much thicker RZ of ∼280 μm characterized by layered microstructure of alternating fine crystalline Al₂O₃ and coarser Al₁₃Co₄ layers. Moreover, at the RZ/CoO interface the presence of a cobalt layer was also identified.