Microstructure and strength of brazed joints of Ti 3Al-base alloy with TiZrNiCu filler metal

Abstract

Brazing of Ti 3Al 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 Ti 3Al alloys with the filler metal TiZrNiCu, namely Ti 2Ni + TiCu intermetallic compounds formed close to the Ti 3Al alloy. TiNi 2Cu intermetallic compounds layer formed between Ti 2Ni + TiCu intermetallic compounds and the filler metal and a Ti[s,s] (here s,s means super saturation) solid solution formed with the dispersed TiNi 2Cu in the middle of the joint. The interfacial structure of brazed Ti 3Al alloys joints with the filler metal TiZrNiCu is Ti 3Al/Ti 2Ni + TiCu/TiNi 2Cu/Ti[s,s] solid solution + TiNi 2Cu/TiNi 2Cu/TiCu + Ti 2Ni/Ti 3Al and this structure will not change with brazing time once it forms. The formation of over many intermetallic compounds Ti 2Ni + TiCu + TiNi 2Cu results in embrittlement of the joint and poor joint properties. The thickness of Ti 2Ni + TiCu + TiNi 2Cu intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity K 0 of the reaction layer Ti 2Ni + TiCu + TiNi 2Cu in the brazed joints of Ti 3Al alloys with the filler metal TiZrNiCu are 261 kJ/mol and 0.0434 mm 2/s, respectively and the growth formula was y 2 = 0.0434 exp(−31392.83/ T) t. Careful control of the growth of the reaction layer Ti 2Ni + TiCu + TiNi 2Cu can influence the final joint strength.