A Study on the Wetting Behaviour of Ti-20Zr-20Cu-20Ni Brazing Filler on Ti-6Al-4V

The brazing of titanium alloys is nowadays a common and necessary industrial practice, because of the wide usage of these alloys in areas such as aerospace and chemical industries. However, to have a successfully brazed joint, it is important for the brazing filler to be able to wet the substrate. Unfortunately, there is a research gap with respect to the study on the wetting and spreading behaviour of brazing fillers on titanium alloys. In this work, wetting behaviour of Ti-20Zr-20Cu-20Ni brazing filler on Ti-6Al-4V was studied using sessile drop technique. Effects of the surface roughness of the substrate and heating scheme on wetting and spreading of the filler metal were evaluated. The degree of wetting was evaluated by measuring the apparent dynamic contact angle and calculating the spread ratio. The wetting mechanism was carefully studied too by the combination of quenching technique and microstructural analyses. Different wetting/spreading regimes were identified. The surface roughness of the substrate was found to have little or no effect on the final apparent contact angle in this work. The wetting behaviour of this system had a reactive nature. High heating rate (6.8oC/s) limited metallurgical reaction between the substrate and the brazing filler, leading to wetting/spreading dominated by the primary stage. With the low heating rate scheme (1.7oC/s), metallurgical reaction between the brazing filler and the substrate was more intense. High heating rate with soaking scheme is recommended for brazing because it entails good spreading and limited metallurgical reaction between the brazing filler and the substrate