Joining of alumina with an alumina–zirconia insert under low mechanical pressure

Two alumina pipes were joined with an alumina–20 mass% zirconia composite insert for 4 and 8 h at 1650 °C and 1700 °C under a low mechanical pressure of 0.05 MPa. Although plate-like voids were observed along the interfaces in the specimens joined at 1650 °C, such voids were replaced with smaller round pores in specimens bonded at 1700 °C owing to local plastic deformation of the insert at the joint interfaces. In addition, the zirconia grains of the insert were deeply incorporated into alumina grains in the parent alumina at the interfaces at 1700 °C. Because of these microstructural effects, the specimens joined at 1700 °C showed relatively high flexural strengths both at room temperature and at 1200 °C that were close to that of the parent alumina, and most of the specimens were fractured from the parent alumina.