Wetting kinetics of AgCuTi filler metal over the TiAl-based alloy substrate under controlled atmosphere conditions

Wetting kinetics of AgCuTi/TiAl brazing system under controlled atmosphere conditions were investigated assisted by a hot-stage microscopy system. Influence of the different shielding gas flow rate on the wetting process, the maximum radius during spreading process, wetting kinetics and interfacial microstructure were studied. Brazing of AgCuTi/TiAl system was conducted under the argon atmosphere with different gas flow rate of 5, 10 and 15 mL/s, respectively. The peak temperature and the dwelling time of the heating-cooling curve was 1273 K and 120 s, respectively. The interfacial microstructure was analyzed by using SEM, EDS and OM. The results showed that shielding gas flow rate had a great impact on the wetting/spreading phenomena:(i) maximum equivalent wetting radius of the molten filler was acquired when the shielding gas flow rate was 15 mL/s, i.e. a maximum radius of 1.4 mm was obtained from the original value of 0.9 mm after brazing;(ii) wetting process of AgCuTi/TiAl system under different protection conditions featured similar kinetics, which can be described using the classical Washburn model, and the radius during spreading showed the power function relationship vs. time, rⁿ~kt; the protection conditions had little impact on the microstructure of the molten filler/TiAl, which features a layered-structure:Ag-rich phase of the residue filler metal/AlCuTi ternary intermetallics(AlCu₂Ti, AlCuTi, Ti₃Al) combined layer/TiAl substrate.