Microstructural characteristics and tensile properties of gas tungsten constricted arc (GTCA) welded Inconel 718 superalloy sheets for aeroengine components

Abstract

Abstract Inconel 718 is a nickel-based superalloy, typically used in high temperature aerospace applications due to its exceptional mechanical properties and weldability. However, it is susceptible to solute segregation and coarser interconnected laves phase evolution in weld metal due to the high heat input in the gas tungsten arc welding (GTAW) process which drastically reduces the tensile properties of welded joints. It is also susceptible to HAZ microfissuring and liquation cracking issues owing to the evolution of low melting temperature eutectic film at the grain boundaries. To overcome this problem, a newly emerged novel gas tungsten constricted arc welding (GTCAW) process, principally differentiated by magnetic arc constriction and high frequency accentuation of the arc, is used to join Inconel 718 superalloy. The primary objective of this investigation is to evaluate the microstructural characteristics and tensile properties of GTCA welded Inconel 718 superalloy sheets (2 mm thick), fabricated using optimized process parameters, and compare its performance with the base metal. Results showed that GTCA welded joints exhibited 99.20 % and 73.5 % of base metal strength and ductility claiming significant advantages over the GTAW process. It is correlated to the grain refinement in the fusion zone and the evolution of finer discrete laves phase in interdendritic areas of the weld. The basic mechanism responsible for fusion zone grain refinement and corresponding influence on tensile properties of joints is also discussed in brief with regard to the mechanics of arc constriction and pulsing.