Effect of welding current modes and post weld heat treatment on microstructure, tensile properties and fracture behavior of gas tungsten arc welded AlCoCrFeNi2.1 EHEA sheets for advanced gas turbine applications

The AlCoCrFeNi 2.1 eutectic high entropy alloy (EHEA) offers greater potential for high temperature applications in advanced gas turbine engines due to its dual phase FCC+BCC microstructure, superior mechanical properties, excellent creep strength and corrosion resistance. However, welding thin EHEA sheets using conventional constant-current gas tungsten arc welding (CC-GTAW) process presents significant high heat input related issues including porosity, excessive weld bead size, coarser dendritic fusion zone (FZ) microstructure and heat-affected zone (HAZ) softening, leading to inferior tensile properties. To address these issues, in this study, the pulsed-current GTAW (PC-GTAW) process characterized by high frequency (300 Hz) welding current pulsation was employed. The main objective of this study is to investigate the effect of welding current modes in GTAW process and post-weld heat treatment (PWHT) on the microstructure, tensile properties, and fracture behavior of AlCoCrFeNi 2.1 EHEA sheets. The 1.5 mm thick as-cast EHEA sheets were welded using CC-GTAW and PC-GTAW processes, followed by PWHT involving solutionizing at 1000 °C for 2 hours (water quenched) and artificial aging at 800 °C for 8 hours (air cooled). The mechanical performance of CC-GTAW and PC-GTAW welds was evaluated using transverse tensile and microhardness tests in as-welded and PWHT conditions. The microstructures of the FZ, HAZ, and base metal zone were examined using optical and scanning electron microscopy (SEM). The phases evolved in the FZ of welds were identified using X-ray diffraction, and elemental analysis was performed using SEM energy dispersive spectroscopy (EDS). Results showed that PC-GTAW welds exhibited superior tensile properties, improved FZ hardness, and minimized HAZ softening compared to CC-GTAW welds, due to significant dendritic refinement in the FZ microstructure and limited grain growth in the HAZ. PWHT enhanced the tensile strength and hardness of both CC-GTAW and PC-GTAW welds, owing to the precipitation of finer needle-shaped secondary B2 BCC phases. However, PC-GTAW welds demonstrated a better response to PWHT, with significant improvements in tensile strength (7.41%), yield strength (9.74%), ductility (55.45%), FZ hardness (7.60%), and HAZ hardness (10.09%) compared to CC-GTAW welds. The findings highlight the benefits of using PC-GTAW and PWHT for enhancing the mechanical properties of EHEA welds, making it a promising technique for advanced gas turbine engine applications. • Microstructural refinement: High-frequency pulsation in PC-GTAW refines FZ microstructure, resulting in equiaxed FCC dendrites with thinner interdendritic B2 BCC phases. • Superior joint performance: PC-GTAW welds exhibit superior tensile properties, improved FZ hardness, and minimized HAZ softening compared to CC-GTAW welds. • Enhanced PWHT response: PC-GTAW welds show better response to PWHT, resulting in significant precipitation hardening of FZ and HAZ. • Improved failure behavior: PC-GTAW welds show a shift in tensile failure location from HAZ to BMZ after PWHT, indicating enhanced mechanical behavior. • Potential application: The PC-GTAW process with PWHT offers a promising approach for welding AlCoCrFeNi 2.1 EHEA advanced gas turbine engine applications.