An overview on welding of Inconel 718 alloy - Effect of welding processes on microstructural evolution and mechanical properties of joints

Inconel 718 is a nickel-ferrous-chromium based superalloy extensively used in the aerospace sector at elevated temperature up to 650 °C due to its better mechanical properties and weldability. However, it is susceptible to some metallurgical problems during welding such as constitutional segregation and consequential Laves phase formation in fusion zone (FZ) which severely deteriorates the service performance of Inconel 718 joints. This alloy also reveals extreme tendency to microfissuring in heat affected zone (HAZ) due to the development of eutectic phases and carbides at the grain boundaries. It causes the premature failure of welded aero-engine components. Gas Tungsten Arc Welding (GTAW) process is comprehensively employed for welding of Inconel 718 alloy to produce high-quality joints. However, the high heat input and lower joint penetration associated with wider bell-shaped arc column principally constrains its application and employability in making the highly efficient joint. The Laves phase formation and HAZ microfissuring can be mitigated by lowering the heat input and increasing the rate of cooling. The electron beam (EBW) and laser beam (LBW) welding have shown significant influence on minimizing the Laves phase formation but they are susceptible to porosity related defects and HAZ liquation cracking due to the rapid rate of cooling. This paper provides an overview of the weldability studies on Inconel 718 alloy. The physical metallurgy of Inconel 718 alloy is explained briefly. The effect of welding processes (GTAW, EBW and LBW) on microstructural characteristics, tensile properties, hardness, hot tensile, stress rupture and corrosion behaviour of Inconel 718 alloy joints is reported and discussed. •The effect of welding processes (GTAW, EBW and LBW) on microstructural characteristics and mechanical properties of Inconel 718 joints are reviewed and discussed.•The Inconel 718 alloy is susceptible to metallurgical problems in welding such as hot cracking, HAZ liquation cracking, segregation and Laves phase formation in fusion zone (FZ).•The GTAW Inconel 718 joints reveal inferior tensile properties (70% joint efficiency) due to the formation of coarser networked Laves phase in FZ.•The EBW and LBW processes are efficient in controlling the Nb segregation (10–12%) and Laves phase formation (4–6%) in FZ of Inconel 718 joints.•GTCAW process disclosed significant advancement in tensile properties of Inconel 718 joints, raising joint efficiency up to