brazing of alumina to zirconia using an oxide filler

Ceramics, due to a variety of properties such as high strength, good wear resistance, electrical insulation, and excellent corrosion resistance, have found many engineering applications. advanced engineering ceramics like alumina and zirconia have unique applications in various fields. to produce assemblies with complex and large shapes, it is sometimes necessary to join small and simple components of these materials. in some applications, it is also demanded to either join ceramic to metal or to other ceramic materials to combine their properties. by using oxide ceramics as fillers, the process can be carried out in a normal atmosphere. on the other hand, oxides have a coefficient of thermal expansion and surface tension close to ceramics, which reduce residual stress and improve wettability, which led to higher joint strength. in this study, brazing of alumina to zirconia was performed using a bi2o3-y2o3 filler in a furnace under ambient atmosphere. as bismuth oxide reacts well with alumina and zirconia, it is expected to form a good bond between them. on the other hand, the presence of yttria in the filler prevents the yttria in the stabilized zirconia to diffuse into the interface, maintaining the stability of the substrate. the wettability of alumina and zirconia substrates with bi2o3-y2o3 and the optimum filler composition were investigated. as a result, a filler with 3% by weight of yttria was selected. following that, joining experiments were performed at 950 and 975 ℃ for 10, 15, and 20 minutes . the brazed samples were examined, and it was found that the samples that were bonded at 975 ℃ were acceptable, while the rest of the samples had little strength and were separated with a minimal stress. the strength of the joints was then measured, which first improved when the temperature and time of the joining process were increased to 975 ℃ and 15 minutes, and eventually declined. the maximum strength was measured to be about 31 mpa. examination of interfacial phases revealed formation of two new phases for which there were no standard xrd id cards. the atomic percentage of the elements constituting these phases was calculated using eds analysis. bi5zr8y21o88 was suggested for a phase created close to the zirconia substrate, and bial8y5o23 was proposed for a phase formed close to the alumina substrate. finally, examination of the fracture surfaces of the joints revealed that increasing the brazing time resulted in an increase in brittle phases generated at the interface, leading to a brittle fracture in the joints.