In the research work, an attempt is made to join nickel-based alloy 825 by employing CO₂ laser beam welding. Successful full penetration weld joint of a 5 mm thick plate is achieved with a very low heat input of 120 J-mm⁻¹. Narrow weld bead width of 0.6 mm at the root and 1.6 mm at the cap is observed fusion zone; the interface and base metal microstructures have been examined using both optical and scanning electron microscopic techniques to understand the microstructural changes which have occurred due to laser welding. A range of tests of Vickers micro hardness, tensile and impact tests had been performed on the weldment to ascertain the mechanical properties of the joint. Tensile failure at the base metal and a 180° root bend test conducted on the weldment ascertain the soundness of the weld joint produced. An attempt is made to correlate the microstructure and mechanical properties of the weldment. Intermetallics TiN and Al₄C₃ observed in the SEM\EDS analysis at the fusion zone are found to have improved the weld metal strength and hardness.

High temperature corrosion resistance of welded components in power plant industry, hot sections of gas turbines, boilers, industrial waste incinerators, metallurgical furnaces and petrochemical installations is one of the serious necessity. The failure of hot sections of welded component is due to the deposition of molten salt which accelerates the hot corrosion reactions in the weld joint. In this research work, the oxy-chlorination of dissimilar weldments between AISI 304L austenitic stainless steel and AISI 4340 alloy steel at 600°C in eutectic mixture of K₂SO₄ + 60% NaCl under molten salt conditions was investigated. Corrosion kinetics for this dissimilar joints calculated from the thermogravimetric charts were represented. Corrosion on the dissimilar joint employing E309L filler in pulsed current gas tungsten arc welding process is found to be very aggressive, due to the fragmented delta ferrites at numerous locations resulting in the formation of the micro electrochemical cells, which act as sites for corrosion initiation and thus leading to higher corrosion rate. However, in the case of continuous current, the joint is able to protect itself better in this environment due to lower amounts of delta ferrites in weld zone, which is attributed to the higher temperature available in continuous mode leading to austenisation of delta ferrites in the multipass welding.

This study aimed to identify the optimal combination of wavelength and laser pulse density to achieve the optimal pulse pressure that can induce the maximum compressive residual stress at the subsurface of microalloyed steel. For this, laser shock peening without coating (LSPwC) was performed on microalloyed steel samples at the fundamental wavelength (1064 nm) with pulse densities of 3, 6, 9, and 12 GW/cm² and at the second harmonic wavelength (532 nm) with pulse densities of 3, 6, and 9 GW/cm². The residual stress distributions were studied to a depth of 500 µm in the laser-treated samples. Tensile residual stress was observed at the surface of laser-peened specimens in both wavelength conditions (1064 and 532 nm). The significant impartment of compressive residual stress across the depth was achieved at the fundamental wavelength (1064 nm). The maximum compressive residual stress was attained with a laser pulse density of 9 GW/cm² in the 1064nm wavelength condition. The optical micrographic analysis in the subsurface regions of the LSPwC specimen at 1064 nm and 9 GW/cm² shows evidence of a high degree of plastic deformation. Electron backscatter diffraction (EBSD) analysis shows that there is grain refinement due to plastic deformations in samples subjected to the fundamental wavelength. Microhardness distribution analysis across the subsurface region shows work-hardening effects in the laser-processed samples in the 1064 nm condition. This study also shows that there is an indication of a thermal softening effect in the samples treated with the 532 nm wavelength, and it is correlated with lower compressive residual stress across the depth.