Influence of InterPulsed TIG Welding Parameters on the Evolution of Microstructure and Tensile Properties of Su-718 Alloy Sheets

Abstract

Abstract Superalloy 718 (Su-718) is a high-performance nickel-based alloy typically employed in high-temperature applications of aero-engine components. It is mostly joined by the Tungsten Inert Gas (TIG) welding process for clean and precise joints. However, the joints are more prone to premature failure owing to the metallurgical problems during solidification, such as constitutional segregation in the fusion zone (FZ) and microfissuring in the heat affected zone (HAZ). To overcome these problems, in this investigation, a recently emerged InterPulsed TIG (IP-TIG) welding process was utilized for joining Su-718 alloy. It is the advanced variant of the TIG welding process principally differentiated by electromagnetic condensation of the arc and high-frequency pulsation up to 20 kHz. The primary objective of this study is to make the potential use of electromagnetic condensation of the arc and pulsation for minimizing the Laves phase growth in FZ and enhancing the tensile strength of joints. To achieve this, the effect of IP-TIG welding parameters on evolution of the microstructure and tensile properties of Su-718 alloy joints is investigated and the results are analyzed in detail in this paper. The analysis of microstructural features was done using optical microscopy, scanning electron microscopy, and Energy Dispersive X-ray Spectroscopy techniques. The influence of Laves phase morphology on the strength and elongation of joints is revealed and correlated to the fracture surface. The principal mechanism responsible for changes in microstructural features and consequential influence on tensile behavior of joints is explained briefly and correlated to the cooling rate and heat input conditions during welding.