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

Brazing of Ti3Al alloys with the filler metal TiZrNiCu was carried out at 1173–1373 K for 60–1200 s. The relationship of brazing parameters and shear strength of the joints was discussed and the optimum brazing parameters were obtained. When products are brazed, the optimum brazing parameters are as follows: brazing temperature is 1273–1323 K, brazing time is 250–300 s. The maximum shear strength of the joint is 250–260 MPa. Four kinds of reaction products were observed to have formed during the brazing of Ti3Al alloys with the filler metal TiZrNiCu, namely Ti2Ni + TiCu intermetallic compounds formed close to the Ti3Al alloy. TiNi2Cu intermetallic compounds layer formed between Ti2Ni + TiCu intermetallic compounds and the filler metal and a Ti[s,s] (here s,s means super saturation) solid solution formed with the dispersed TiNi2Cu in the middle of the joint. The interfacial structure of brazed Ti3Al alloys joints with the filler metal TiZrNiCu is Ti3Al/Ti2Ni + TiCu/TiNi2Cu/Ti[s,s] solid solution + TiNi2Cu/TiNi2Cu/TiCu + Ti2Ni/Ti3Al and this structure will not change with brazing time once it forms. The formation of over many intermetallic compounds Ti2Ni + TiCu + TiNi2Cu results in embrittlement of the joint and poor joint properties. The thickness of Ti2Ni + TiCu + TiNi2Cu intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity K0 of the reaction layer Ti2Ni + TiCu + TiNi2Cu in the brazed joints of Ti3Al alloys with the filler metal TiZrNiCu are 261 kJ/mol and 0.0434 mm2/s, respectively and the growth formula was y2 = 0.0434 exp(−31392.83/T)t. Careful control of the growth of the reaction layer Ti2Ni + TiCu + TiNi2Cu can influence the final joint strength.