Effect of welding parameters on microstructure and tensile properties of CA-TIG welded AMS-5596 grade thin high temperature alloy sheets for gas turbine engine applications

Abstract

This paper presents the influence of Constricted Arc TIG (CA-TIG) welding parameters specifically Main Current (MC), Arc Constriction Current (ACC), ACC Frequency (ACCF) and Constricted Arc Traverse Speed (CATS) on weld bead, microstructure and tensile properties of Superalloy 718 joints. The mechanisms responsible for microstructural modification and consequential influence on tensile properties of joints are discussed in brief. The results showed that MC and CATS extend predominant influence on the weld bead geometrical features, growth of dendrites, volume % and morphology of laves precipitates in fusion zone (FZ) and tensile properties of Superalloy 718 joints than ACC and ACCF. The tensile properties of joints decrease at higher levels of MC (80 A), ACC (60 A) and ACCF (20 ​kHz) due to the high heat input which supresses the refinement of dendritic FZ microstructure. The tensile properties of joints increase at incremental levels of CATS due to the reduced heat input leading to the refinement of dendritic FZ microstructure. However, the joints exhibit poor tensile properties at higher level of CATS (80 ​mm/min) due to the insufficient heat input leading to partial penetration of joints. The joints made using MC of 65 A, ACC of 50 A, ACCF of 4 ​kHz and CATS of 60 ​mm/min yielded 99.20% joint efficiency and 27.93% ductility which is much higher than TIG welding process. It is attributed to the refinement of FZ dendritic structure and development of finer laves precipitates by virtue of constricted arc and high frequency pulsation of ACC.