Direct active soldering of micro-arc oxidized Ti/Ti joints in air using Sn3.5Ag0.5Cu4Ti(RE) filler

Porous titanium dioxide films were fabricated on commercial pure Ti (Ti) plates by micro-arc oxidation (MAO). Direct active soldering of Ti/Ti, MAO-TiO2/MAO-TiO2, and Ti/MAO-TiO2 was performed at 250 °C using Sn3.5Ag0.5Cu4Ti active solder doped with trace rare-earth elements (RE). The joining process was done without flux and without the need of pre-metallization of the Ti and MAO-TiO2 substrate samples or a protective atmosphere. The bond shear strengths of Ti/Ti, MAO-TiO2/MAO-TiO2, and MAO-TiO2/Ti joints were determined to be 16.5±1.28, 11.85±1.18, and 11.75±1.43 MPa, respectively. It was also found that trace RE content has effects on the interfacial reactions at the active solder/MAO-TiO2 interfaces, and subsequently nano-Ag3Sn particles adsorb at the active solder/MAO-TiO2 interfaces. acture of Ti/Ti joints was found to mainly propagate along the grain boundary. In the MAO-TiO2/MAO-TiO2 and MAO-TiO2/Ti samples, the failure mode transitioned from MAO-TiO2 layer/Ti interfacial fracture to fracture within the active solder.