Pulsed Nd:YAG laser beam welding (P-LBW) and pulsed tungsten inert gas (P-TIG) welding were used to prepare full penetration bead-on-plate weldments of 1.6 mm thick Ti-5Al-2.5Sn alpha titanium alloy sheet. The influence of welding phenomenon on the microstructure, micro-hardness, tensile properties, surface and sub-surface residual stress distribution and deformation and distortion of both the weldments were studied. Higher cooling rate in P-LBW resulted in complete ␣' martensitic transformation in fusion zone whereas in P-TIG weldment ␣' and acicular ␣ was formed within equiaxed ␤ matrix due to lower cooling rate. Hardness in fusion zone of P-LBW was higher than that of the fusion zone of P-TIG weldment due to faster cooling rate in P-LBW. The welded zone in both the weldments showed higher hardness and strength than that of the parent metal since a ductile fracture occurred in the un-welded section during tensile testing. Residual stresses in both P-LBW and P-TIG weldments showed similar trend but the distribution was much narrower in P-LBW due to less width of heat affected zone. P-LBW resulted in more nonuniformity in through thickness stress profile because of greater top to bottom width ratio. Less residual stresses, deformation and distortion and superior mechanical properties in P-LBW made the process more feasible than P-TIG for the welding of Ti-5Al-2.5Sn alloy sheet.

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Electron beam welding (EBW), pulsed Nd:YAG laser beam welding (P-LBW), and pulsed tungsten inert gas (P-TIG) welding of Ti–5Al–2.5Sn alloy were performed in order to prepare full penetration weldments. Owing to relatively high power density of EBW and LBW, the fusion zone width of EBW weldment was approximately equal to P-LBW weldment. The absence of shielding gas due to vacuum environment in EBW was beneficial to the joint quality (low oxide contents). However, less cooling rates were achieved compared to P-LBW as an increase in heat-affected zone width and partial α′ martensitic transformation in fusion zone were observed in EBW weldments. The microstructure in fusion zone in both the EBW and P-TIG weldments comprised of both acicular α and α′ martensite within the prior β grains. Hardness of the fusion zone in EBW was higher than the fusion zone of P-TIG but less than the fusion zone of P-LBW weldments due to the observed microstructural differences. Notch tensile specimen of P-LBW showed higher load capacity, ductility and absorbed energy as compared to P-TIG and EBW specimens due to the presence of high strength α′ martensite phase. Maximum sheet distortions and tensile residual stresses were observed in P-TIG weldments due to high overall heat input. The lowest residual stresses were found in P-LBW weldments, which were tensile in nature. This was owing to high power density and higher cooling rates in P-LBW operation. EBW weldment exhibited the highest compressive residual stresses due to which the service life of EBW weldment is expected to improve.

In a dissimilar welded joint between Ni base alloys and titanium, creep failure is a potential concern as it could threaten to undermine the integrity of the joint. In this research, the mechanical heterogeneity of a Pulsed TIG welded joint between commercially pure titanium (CpTi) and Inconel 718 (IN718) with a vanadium (V) interlayer was studied through a nanoindentation technique with respect to hardness, elastic modulus, and ambient temperature creep deformation across all regions (fusion zones and interfaces, mainly composed of a dendritic morphology). According to the experimental results, a nanohardness of approximately 10 GPa was observed at the V/IN718 interface, which was almost 70% higher than that at the V/CpTi interface. This happened due to the formation of intermetallic compounds (IMCs) (e.g., Ti2Ni, NiV3, NiTi) and a (Ti, V) solid solution at the V/IN718 and V/CpTi interfaces, respectively. In addition, nanohardness at the V/IN718 interface was inhomogeneous as compared to that at the V/CpTi interface. Creep deformation behavior at the IN718 side was relatively higher than that at different regions on the CpTi side. The decreased plastic deformation or creep effect of the IMCs could be attributed to their higher hardness value. Compared to the base metals (CpTi and IN718), the IMCs exhibited a strain hardening effect. The calculated values of the creep stress exponent were found in the range of 1.51–3.52 and 2.52–4.15 in the V/CpTi and V/IN718 interfaces, respectively. Furthermore, the results indicated that the creep mechanism could have been due to diffusional creep and dislocation climb.