Microstructure evolution of alumina/alumina joint bonded by boron oxide-alumina nonmetal powder interlayer

Alumina was successfully joined to itself in air environment by B₂O₃ + Al₂O₃ powder mixture as the interlayer to synthesize aluminum borate whiskers in the joint. The microstructure evolution was analyzed by means of scanning electron microscope (SEM) and X-ray diffraction (XRD). The possible mechanism of microstructure evolution was also discussed. The effects of parameters such as heating cycles and temperature on the microstructure as well as the 3-point flexural strength of the joint were investigated. It was found that heating the specimen for several heating cycles instead of holding at a constant temperature for a long time can eliminate the voids among the whiskers to achieve a dense microstructure, and the phenomenon that higher temperatures can accelerate the reaction was also observed. The highest strength of the joint reaches 90.29MPa with the heating temperature of 800°C after four heating cycles.