Elimination mechanism of voids caused by density differences in high crystallinity alumina/alumina joints bonded with dysprosium aluminum silicate glass ceramic filler

Abstract

In this work, the Dy2O3-Al2O3-SiO2 (DASN) and Dy2O3-Al2O3-SiO2-TiO2 (DAST) glass fillers were used for joining alumina ceramic. During the cooling process of the alumina/DASN/alumina joints, Dy2Si2O7 and Al2O3 were precipitated simultaneously and gradually grown. As a result, voids were formed due to the poor flowability of the glass ceramic filler and the large density difference between the glass filler and Dy2Si2O7 crystals. On the contrary, the addition of TiO2 altered the sequence of the crystalline phase precipitation during the cooling process. During cooling from the joining temperature (1450 °C) to 1100 °C, only Dy2Si2O7 was formed in the brazing seam. Simultaneously, the flowing glass phase was able to fill the spaces caused by the density differences. When the growth of Dy2Si2O7 phase ceased, the Al2O3 phase began to precipitate. Therefore, the voids caused by density differences can be eliminated in the alumina/DAST/alumina joints with high crystallinity. The optimal flexural strength of alumina/DAST/alumina joints tested at room temperature and 1000 °C reached 350 MPa and 158 MPa, respectively.