Microstructures And Properties Of Brazing Joint Of Al₂o₃ Ceramic And Q235 Steel

To achieve a solid connection between Al₂O₃ ceramics and Q235 steel can play the excellent high-temperature performance, corrosion resistance, wear resistance of ceramic materials, and can also take full advantage of easy processing characteristics of metallic materials, which is extremely important in both theory and practice. In this research, Al₂O₃ ceramics were bonded with Q235 steel by active brazing with the filler alloys of Cu-Ti. The wetting properties of Cu-Ti active filler alloy were studied, and effects of the composition of filler alloys and brazing parameters such as temperature, holding time on joining strength and interface microstructures were investigated and analyzed by means of SEM,EDS,XRD and precision universal testing machine, etc. The interfacial properties and the fracture model of the joints were also discussed.The experimental results showed that the content of Ti in filler had an immediate impact on the wettability of the filler alloy, and the wettability increased with increasing Ti content in the experimental alloy composition range. The microstructure and properties of the joint depended on the composition of filler alloy and brazing parameters. Different shear strength of the joints was obtained as a result of different interface microstructures when using filler alloys with different ratios. Too high or too low brazing temperatures and too long or too short holding times were not conducive to obtain joints with good performance and compact organizations. When brazed at 1050℃for 30min with a filler alloy of Cu75Ti25 and exerted a pressure of 74Pa, a best joint was obtained with compact and few defects such as cracks and micropores in the interfacial-binding region and the average shear strength of the joint is 99.3MPa.The analysis of microstructure of the joints showed that interface-binding region could be divided into three layers. The three layers were reaction layer close to the ceramic, brazing alloy layer and diffusion layer close to the steel. The liquid braze alloy filled the micropores of ceramic and formed the reaction layer. Cu₃Ti₃O, TiFe, TiFe₂ and Cu-base solid solution were confirmed as the reaction products. A metallurgical bonding had been achieved between the ceramics and the steel. According to the research of interfacial properties of the brazed joint, the hardness of interfacial zone was higher than the Q235 steel, and the hardness of the interfacial zone smoothed their transition, which indicated an excellent joint.Different bonding strength of brazed joints showed different characteristics of the shear fracture. There were two fracture modes of the joints, when the bonding strength was high, the fracture occurred in the ceramic side completely, when the bonding strength was low, the fracture occurred in the interface of ceramic and metal.