Effect of activated flux GTAW with AlCoCrFeNi2.1 eutectic high entropy alloy interlayer on microstructure and mechanical properties of dissimilar P91/304 L steel joints

In this study, the effect of activated flux gas tungsten arc welding (GTAW) with AlCoCrFeNi_2.1 eutectic high entropy alloy interlayer on the microstructure and mechanical properties of dissimilar P91/304 L steel joints was studied and the results were compared with the joints welded using the traditional multi-pass GTAW with Inconel 82 filler for its validity in practical applications. The higher overall heat input in multi-pass GTAW and lower solubility of strengthening elements in completely austenitic weld metal deteriorated the mechanical properties of joints. The eutectic high-entropy alloy interlayer imparted a high-entropy effect to the weld metal, resulting in increased mixing entropy and sluggish diffusion behavior. This led to better mixing of the weld metal and a functionally graded structure with minimized unmixed zones, lower carbon migration and reduced peak hardness at the weld metal interface. The flux-assisted arc constriction and reversal of the Marangoni convection effect in activated flux GTAW enabled deeper penetration with lower heat input in two passes compared to the traditional approach. The increased cobalt content (1.36 wt%) in the weld metal suppressed the delta ferrite formation and imparted grain refinement by promoting secondary phase precipitation at the grain boundaries and strengthening the weld metal. The lower heat input in activated flux GTAW with higher nickel and cobalt content in eutectic high entropy alloy interlayer tailored a refined dual phase austenitic-martensitic microstructure with finer discrete secondary phases in weld metal resulting in superior mechanical properties compared to the traditionally welded joints in as-welded state. Thereby eliminates post-weld heat treatment.