Effect of Pre-cold Deformation and Welding Current Mode on Mechanical Properties and Microstructure of GTAWed Nimonic ۸۰A Superalloy

This study investigates the microstructural evolution and variations in the mechanical properties of pre-cold worked Nimonic ۸۰A superalloy, subjected to two levels of deformation (۲۵% and ۵۰%) and welded via Gas Tungsten Arc Welding (GTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) techniques using ER۳۰۹L filler wire. The objective is to evaluate the effect of the initial microstructure on the welding behavior of Nimonic ۸۰A and compare the weldments produced using GTAW and PCGTAW. Microstructural characterization was conducted using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). XRD analysis demonstrated that the welding pulsed current mode, compared to the continuous current mode and at equal heat input, led to a refined microstructure, suggesting improved welded mechanical properties of the weld. It also showed a potential reduction in grain refinement with a higher level of cold work. Tensile testing demonstrated that fractures consistently occurred within the weld zone (WZ), with the PCGTAW sample achieving the highest tensile strength (۷۶۶ MPa). Microhardness analysis indicated a notable reduction in hardness within the heat-affected zone (HAZ) and WZ, particularly in the ۵۰% pre-cold worked sample. However, PCGTAW retained higher hardness due to its refined microstructure. The weld metal primarily consisted of an austenitic microstructure characterized by dendrites and interdendritic precipitates. Microstructural analysis revealed that welding induced significant changes in the weldment, with the PCGTAW sample exhibiting a more uniform microstructure and smoother transitions at the weld interface. Fractography confirmed ductile fracture in all specimens, with smoother and more uniformly distributed dimples in the PCGTAW sample. These findings highlight the advantages of pulsed current welding in optimizing the mechanical performance of Nimonic ۸۰A welds and suggest its potential application in industries requiring superior weld quality.

کلیدواژه ها:

Nimonic ۸۰A Superalloy ، GTAW Welding ، Pre-Cold Worked ، Initial Microstructure ، PCGTAW Process.