Insights into Microstructure Evolution and Mechanical Properties of Linear friction welding of Dissimilar Ti2AlNb and Ti60 Alloys

In this study, microstructure evolution and the interface metallurgical bond of linear friction welded dissimilar Ti ₂ AlNb/Ti60 joint were studied. The relationship of microstructure to tensile and impact strength of the joint were analyzed. Results show that continuous dynamic recrystallization occurred on two weld zones (WZ) during welding, forming equiaxed fine grains which were smaller than those of the two base metals. On the Ti60 side thermo-mechanically affected zone, α grains were elongated under the high temperature and shear force effects; while on the Ti ₂ AlNb side, the large B2 grains were also elongated where a large number of O phases were dissolved. In the Ti ₂ AlNb side heat affected zone, the B2 grains were not deformed, and the O phases inside B2 grains were decomposed, as the welding temperature was lower than that in the TMAZ. The interface metallurgical bond was achieved through mutual diffusion of Ti, Al and Nb, producing an element transition layer of 1.54 µm composed of TiAl ₃ and NbAl ₃ intermetallic compounds. The tensile strength of the joint was 920 MPa, which is 97.9% of the Ti60 BM, but elongation was 1.7%. Failure of joint during tensile strength testing was located at the junction of Ti ₂ AlNb side TMAZ and HAZ, where the O phases dissolve and there was no dynamic recrystallization of the B2 grains. So, the plastic deformation of the joint when a tensile load was applied was concentrated there, producing limited elongation. The impact energy at interface was measured to be 13.0 J/cm², which is higher than that of Ti ₂ AlNb BM, as the toughness of the interface is better than that of Ti ₂ AlNb BM, which is related to TiAl ₃ and NbAl ₃ intermetallic compounds forming at the interface element transition layer.