Wettability and Interfacial Reaction between Molten lron and Zirconia Substrates

The surface tension of, and the contact angle formed by, molten iron on three types of commercial zirconia substrates containing 8 mol% Y₂O₃, 9 mol% MgO, or 11 mol% CaO were measured over a wide range of oxygen concentration in the molten iron by the sessile drop method. The solidified metal–substrate interface was examined in an SEM equipped with an EPMA. The surface tension of molten iron decreased with increasing oxygen concentration. The contact angle of molten iron increased rapidly with increasing oxygen concentration and reached a local maximum value at an oxgyen concentration of ∼100 ppm, and then decreased with increasing oxygen concentration. At lower oxygen concentration, dissociation of ZrO₂ was observed. For the ZrO₂–9 mol% MgO substrate, segregation of MgO to the interface was observed. For the ZrO₂–11 mol% CaO substrate, segregation of CaO and the precipitation of small ZrO₂ particles in the segregation layer of CaO were observed at the interface. Conversely, at higher oxygen concentration, penetration of molten iron into the grain boundaries was observed in all types of zirconia substrates.