Improvement of Metallurgical and Mechanical Properties of Gas Tungsten arc Weldments of Alloy 686 by Current Pulsing

Abstract

This research article examines the metallurgical and mechanical behavior of twenty-first-century nickel-based superalloy 686. The weld joints were produced with ERNiCrMo-4 and ERNiCrMo-14 filler wires by continuous current gas tungsten arc welding (GTAW) and pulsed current gas tungsten arc welding (PCGTAW) mode. Optical and scanning electron microscope (SEM) analyses were performed to evaluate the microstructure of welded joints. PCGTAW weldments showed refined microstructure, narrower weld bead and minimum heat-affected zone compared to GTAW. SEM analysis revealed the presence of secondary phases in the interdendritic regions of GTA and PCGTA weldments made of ERNiCrMo-4 and GTA ERNiCrMo-14 fillers. Energy-dispersive X-ray spectroscopy examination was also performed to assess the microsegregation of alloying elements in the weldments. The results proved nonexistence of microsegregation in the case of PCGTA weldments made by ERNiCrMo-14 filler. However, segregation of alloying element Mo was noticed in other weldments. Strength and toughness of the weld joints were evaluated by conducting tensile and Charpy impact tests. The refined microstructure with the absence of microsegregation obtained in the PCGTA welding made with ERNiCrMo-14 filler wire resulted in the higher strength and toughness than other weldments.