A novel nucleation and growth phenomenon for TiAl3 intermetallic phase in Ti/Al diffusion couple is proposed based on diffusion kinetics. The interdiffusion and intrinsic diffusion co-efficients are calculated to make evident of dominant diffusion of Al towards Ti in Ti/Al diffusion couple obtained by solid state diffusion bonding. It was surprising to observe that the diffusion rate of Al was around 20 times higher than Ti with the formation of Kirkendall pores near the Al/TiAl3 interface. With such dominant diffusion of Al towards Ti, the nucleation and growth of TiAl3 intermetallic phase in Ti/Al couple happens mainly at the Ti/TiAl3 interface rather than Al/TiAl3 interface which is evident by the presence of very fine nearly nano-sized TiAl3 nuclei/grains near the Ti/TiAl3 interface. Even though the intermetallic phase is expected to nucleate at Al/TiAl3 interface, the relatively larger TiAl3 grains near that interface depicts grain growth with minimal nucleation. The theoretical calculations on diffusion parameters are in accordance with experimental observations of TiAl3 intermetallic growth phenomenon in Ti/Al system.

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The effect of gas tungsten arc welding (GTAW) process parameters and its impact on the titanium TWB was studied experimentally as well as using numerical simulation. Bead characteristics of BoP trials (bead on plate) were analyzed based on Taguchi L 27 orthogonal array by taking welding current (115 A, 125 A, 135 A), welding speed (4.1 mm/s, 5.8 mm/s, 7.5 mm/s) and arc length (3 mm, 4 mm, 5 mm) as process parameters. The bead width and depth of penetration for all trials were measured by using the weld expert system. Based on the bead characteristics, optimized GTAW process parameters (135 A, 4.1 mm/s and 3 mm) were identified for making the TWB by joining 2-1.6-mm-thick Ti-6Al-4V sheets. The tensile test of the prepared Ti-6Al-4V TWB was conducted in the universal testing machine. The COMSOL and ABAQUS software packages were used for the numerical simulation of TWB to assess the bead profile and tensile properties. The prediction made from the temperature distribution curve related to phase change near weld zone, exactly matched with the experimental work. The joint strength of TWB observed to be around 982 MPa and 1005 MPa was evaluated experimentally and conducting ABAQUS simulation work. The tensile test results were comparable with each other within the acceptable error level.

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