Similarities and differences in the interfacial microstructure and mechanical properties of alumina/alumina joints bonded with dysprosium- and neodymium-aluminosilicate glass filler

In this study, dysprosium-aluminosilicate (DAS) and neodymium-aluminosilicate (NAS) glasses with high softening temperature were used as fillers to join alumina ceramics. The similarities and differences in the interfacial microstructure and flexural strength of the joints were investigated. Results showed that the glass fillers both could infiltrate into alumina ceramics during the joining process. However, excessive infiltration at high joining temperatures led to the formation of pore defects in the brazing seam. An interfacial reaction layer composed of Dy3Al5O12 was formed at the DAS glass/alumina interface. In contrast, no interfacial reaction was observed between the NAS glass and alumina ceramic. Slower cooling rate promoted the crystallization of Dy2Si2O7 and Al2O3 in the Al2O3/DAS/Al2O3 joints, and only Nd2Si2O7 in the Al2O3/NAS/Al2O3 joints. The flexural strength at room temperature of both joints first increased and then decreased with the increased of joining temperature, and showed a declined tendency with the decrease in cooling rate. The flexural strength at 900 °C of Al2O3/DAS/Al2O3 joints reached 245 MPa, which is higher than that of Al2O3/NAS/Al2O3 joints.