Characterization of rare earth oxide-rich glass applied to the glass-infiltration of a ceramic system

The viability of a silica glass containing rare earth oxides as infiltration agents in different ceramic substrates was investigated. ZrO2(Y2O3)–Al2O3 and Al2O3–ZrO2(Y2O3) composite ceramics were sintered at 1530 °C/2 h and characterized by X-ray diffraction (XRD), dilatometry and atomic force microscopy (AFM). The wetting behavior of the substrates by rare earth glass was studied by the sessile drop method at temperatures of up to 1285 °C in an argon atmosphere. Both composites presented high relative density (close to 98%) with α-Al2O3 and tetragonal ZrO2 as crystalline phases. The wetting angle of the two substrates decreased in response to increasing temperature, reaching a final contact angle of 12.7° on the ZrO2(Y2O3):Al2O3 substrate at 1285 °C and of 13.6° on the Al2O3:ZrO2(Y2O3) substrate at 1275 °C, indicating good wettability in both cases. Results of fracture toughness show KIC of 4.3 MPa m1/2 and 5.4 MPa m1/2 for ZrO2(Y2O3):Al2O3 and Al2O3:ZrO2(Y2O3) respectively. The theoretical residual stress in the two infiltrated composites were calculated based on the coefficient of thermal expansion of the substrates and glass. The ZrO2(Y2O3):Al2O3 and Al2O3:ZrO2(Y2O3) composites showed calculated residual stresses of 36.5 MPa (tensile) and 252 MPa (compression), respectively, indicating that compressive residual stress contributes to increase the toughness of the glass-infiltrated composites.