Microstructural Studies on Laser Dissimilar Welded Ni and Steel Alloys for Aeronautical Turbine Applications
V. Dillibabu, M. Duraiselvam, U. Chandrasekhar and R. Raju
CO2 laser welding of Ni alloy and high temperature steel alloy was carried out on a hollow tubular specimen by varying the laser power and weld speed. Preheating of the specimen and offsetting the laser beam from the centre of the weld joint was adopted as primary strategies to overcome the thermal gradient mismatch which is common in welding of dissimilar materials. The microstructure and hardness were analysed using an optical microscope, a scanning electron microscope (SEM) and a Vickers hardness tester. Welding with laser beam centred at the joint interface caused severe reduction in hardness in the fusion zone. Preheating resulted in cracks in the weld zone. It is observed that laser welding with offset towards Ni specimen had resulted in a weld with full penetration, optimum hardness and without any crack.
Keywords: CO2 laser, Ni alloy, steel alloy, dissimilar welding, microstructure, microhardness, turbine