Lasers in Eng., Vol. 0, pp. 1–14 Reprints available directly from the publisher Photocopying permitted by license only 1 *Corresponding author: Tel: +91 (0)9489066240; E-mail: durai@nitt.edu ©2016 Old City Publishing, Inc. Published by license under the OCP Science imprint, a member of the Old City Publishing Group Microstructural Studies on Laser Dissimilar Welded Ni and Steel Alloys for Aeronautical Turbine Applications V. DILLIBABU 1 , M. DURAISELVAM 2, *, U. CHANDRASEKHAR 3 AND R. RAJU 2 1 Gas Turbine Research Establishment, Defence Research and Development Organisation, Banga- lore-560 093, Karnataka, India 2 Department of Production Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India 3 ESCI – The Institution of Engineers (India), Hyderabad, India CO 2 laser welding of Ni alloy and high temperature steel alloy was car- ried 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. Preheat- ing 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 penetra- tion, optimum hardness and without any crack. Keywords: CO 2 laser, Ni alloy, steel alloy, dissimilar welding, microstructure, microhardness, turbine 1 INTRODUCTION Aero-engine applications often demand hardware to meet contradicting requirements. Mechanical and physical properties of these hardware could not be engineered to meet the requirements. In such cases, it is essential to