Wetting and spreading of bulk liquid and precursor film of molten AgCuTi on ultrafast laser structured surface of Ti

Abstract

In order to reveal the influence of special surface structures on the wetting and spreading of Ag/Ti system and the precursor film, micro-bumps, micro-pits, micro-grooves and micro-thread surface structures were machined on a grade 2 commercially-pure Ti (TA2) surface by using ultrafast laser. In situ wetting experiments of AgCuTi filler metal on TA2 surfaces with different special structures were conducted. The results showed that the wetting morphology of AgCuTi over original TA2 surface is special double ring (small circle inside and ring outside). The special surface structures can effectively change the wetting characteristics of Ag/Ti system, including the spreading rate and the final spreading area. It also affects the structure and composition of the wetting interface. In Ag/Ti system, different components are affected to different degrees by the surface structures, resulting in uneven distribution of the bulk liquid region and the precursor film region of the wetting interface. The micro-bumps and micro-pits structures can effectively promote the wetting and spreading of AgCuTi on TA2, while micro-thread structures can inhibit its wetting spread. For the micro-grooves, the AgCuTi spreads rapidly and almost completely along the direction of the groove, while in the vertical direction, it is difficult for the AgCuTi to spread through the groove. By studying the wetting spreading process and interface behavior of molten filler metal on complex surfaces, it is expected to provide important guiding significance for using special surface microstructure to control the wetting spreading process and interface reaction of brazing system.