Microstructure and strength of brazed joints of Ti₃Al base alloy with Cu-P filler metal

Brazing of Ti₃Al alloys with the filler metal Cu-P was carried out at 1173-1273 K for 60-1800 s. When products are brazed, the optimum brazing parameters are as follows: brazing temperature is 1215-1225 K; brazing time is 250-300 s. Four kinds of reaction products were observed during the brazing of Ti₃Al alloys with the filler metal Cu-P, i.e., Ti₃Al phase with a small quantity of Cu (Ti₃Al(Cu)) formed close to the Ti₃Al alloy; the TiCu intermetallic compounds layer and the Cu₃P intermetallic compounds layer formed between Ti₃Al(Cu) and the filler metal, and a Cu-base solid solution formed with the dispersed Cu₃P in the middle of the joint. The interfacial structure of brazed Ti₃Al alloys joints with the filler metal Cu-P is Ti₃Al/Ti₃Al(Cu)/TiCu/Cu₃P/Cu solid solution (Cu₃P)/ Cu₃P/TiCu/Ti₃Al(Cu)/Ti₃Al, and this structure will not change with brazing time once it forms. The thickness of TiCu+Cu₃P intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity K₀ of reaction layer TiCu+Cu₃P in the brazed joints of Ti₃Al alloys with the filler metal Cu-P are 286 kJ/mol and 0.0821 m²/s, respectively, and growth formula was y²=0.0821exp(-34421.59/T)t. Careful control of the growth for the reaction layer TiCu+Cu₃P can influence the final joint strength. The formation of the intermetallic compounds TiCu+Cu₃P results in embrittlement of the joint and poor joint properties. The Cu-P filler metal is not fit for obtaining a high-quality joint of Ti₃Al brazed.