Microstructure and strength of brazed joints of Ti 3Al-base alloy with NiCrSiB

Abstract

Brazing of Ti 3Al alloys with the filler metal NiCrSiB was carried out at 1273–1373 K for 60–1800 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 1323–1373 K, brazing time is 250–300 s. The maximum shear strength of the joint is 240–250 MPa. Three kinds of reaction products were observed to have formed during the brazing of Ti 3Al alloys with the filler metal NiCrSiB, namely, TiAl 3 (TiB 2) intermetallic compounds formed close to the Ti 3Al alloy. TiAl 3+AlNi 2Ti (TiB 2) intermetallic compounds layer formed between TiAl 3 (TiB 2) intermetallic compounds and the filler metal and a Ni[s,s] solid solution formed in the middle of the joint. The interfacial structure of brazed Ti 3Al alloy joints with the filler metal NiCrSiB is Ti 3Al/TiAl 3 (TiB 2)/TiAl 3+AlNi 2Ti (TiB 2)/Ni[s,s] solid solution/TiAl 3+AlNi 2Ti (TiB 2)/TiAl 3 (TiB 2)/Ti 3Al, and this structure will not change with brazing time once it forms. The formation of over many intermetallic compounds TiAl 3+AlNi 2Ti (TiB 2) results in embrittlement of the joint and poor joint properties. The thickness of TiAl 3+AlNi 2Ti (TiB 2) 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 TiAl 3+AlNi 2Ti (TiB 2) in the brazed joints of Ti 3Al alloys with the filler metal NiCrSiB are 349 kJ/mol and 24.02 mm 2/s, respectively, and the growth formula was y 2=24.04exp(−41977.39/ T) t. Careful control of the growth of the reaction layer TiAl 3+AlNi 2Ti (TiB 2) can influence the final joint strength.