Characterization of microstructure and mechanical properties of Super Ni 718 alloy and AISI 316L dissimilar weldments
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The present investigation addressed the weldability of Super Ni 718 alloy and AISI 316L using gas tungsten arc (GTA) welding process using three different filler wires, such as ER2594, ERNiCrMo-4 and ERNiCrCoMo-1. Interface microstructures showed the formation of secondary phases at the heat-affected zone (HAZ) of Super Ni 718 alloy and delta ferrite colonies at the HAZ of AISI 316L. It was witnessed from the weld microstructures that the deleterious phases were suppressed or controlled while using these filler wires for joining the bimetals. Tensile results corroborated that the failure occurred at the parent metal of AISI 316L in all the cases. The presence of microvoids and dimples characterized for the ductile mode of fracture in these weldments. Charpy V-notch test results showed that the weldments using ERNiCrMo-4 filler exhibited higher impact energy. A detailed study has been made to investigate the structure–property relationships of these weldments using optical and scanning electron microscopic techniques.
I. INTRODUCTION
Dissimilar metal welding has been practiced in industries, as it offers combinations of properties that accrue benefits in terms of reduction in material costs and offers design flexibility. However, welding of dissimilar metals is challenging and a cumbersome task due to the differences existing in chemical composition and coefficient of thermal expansion which leads to several drawbacks in metallurgical and mechanical properties.1,2 Both Super Ni 718 alloy and AISI 316L are widely used in industries owing to their good mechanical properties. Super Ni 718 alloy exhibits extraordinary resistance to oxidation and corrosion at elevated temperatures. Similarly, austenitic stainless steel, AISI 316L, has better corrosion and oxidation resistance due to higher amounts of Cr and Ni. Dissimilar combinations of Super Ni 718 alloy and AISI 316L have been widely used in versatile engineering applications such as aerospace engine components, chemical processing equipment, oil and gas industry and power plants. Bimetallic combinations of Super Ni 718 alloy and AISI 316L were used by Alstom Power Sweden in the manufacture of gas turbine engines. It was reported that the GT10B has 10-stage compressor rotors, in which the final four high-pressure stages were made from Super Ni 718 (Inconel 718) disks, and the lower pressure stages were made of austenitic stainless steel. Ferretti et al.3 reported that the bimetallic combinations obtained from a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.329 J. Mater. Res., Vol. 29, No. 24, Dec 28, 2014
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orbital TIG welding were widely used in the International Space Station of Italy. The major problems addressed by various researchers while welding Super Ni 718 alloy are solidification cracking, liquation cracking, microfissuring at heataffected zones (HAZs), and the formation of deleterious phase such as delta and Laves phases. It was reported that the Laves phase is a Nb-
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