Microstructure evolution and local strengthening mechanisms in CoCrFeMnNi high entropy alloy joints reinforced with Inconel 625

In the fusion-based welding processes, filler materials are commonly used to adjust and improve the composition of the fusion zone with the aim of optimizing both microstructure and mechanical properties. However, in the field of welding high entropy alloys, the influence of different filler materials on the microstructure and mechanical response is still scarce, owing to the yet incipient usage of welding technologies for these novel, advanced engineering alloys. To bridge this knowledge gap, Inconel 625 filler wire was used during gas metal arc welding of the well-known CoCrFeMnNi high entropy alloy. To systematically analyze the microstructure evolution and mechanical properties of the welded joints, multiscale characterization techniques were employed. It is shown that the different regions of the welded joint possess distinct microstructural features due to the weld thermal cycle, which is further compounded in the fusion zone by the introduction of the filler material. The use of Inconel 625 filler promotes a solid solution strengthening effect in the fusion zone and became the main contributor to the yield strength of this region (302 MPa (via solid solution strengthening) vs 478 MPa (yield stress from tensile experiments). Since Hall-Petch strengthening is predominant in both base material and heat affected zone, but not on the fusion zone due to the large grain structure that developed, the addition of Inconel 625 filler demonstrates to be a feasible approach to increase the typically low fusion zone strength. By coupling microstructural characterization with mechanical property analysis, aided by the calculation of the strengthening mechanisms, we unveil processing, microstructure, property relationships, providing a broader basis for the widespread application of gas metal arc welding for high entropy alloys. • Gas metal arc welding of rolled CoCrFeMnNi with Inconel 625 filler produced a fully penetrated, defect-free joint. • Recrystallization and grain coarsening in the HAZ relieved strain energy, while rapid solidification formed coarse columnar dendrites (≈350 μm) with Laves phases and Nb-rich carbides. • Thermodynamic calculations accurately predicted non-equilibrium solidification pathways and phase formation in the fusion zone, validated by synchrotron X-ray diffraction. • Hall-Petch strengthening dominated in the base material (≈282.9 MPa) and heat affected zone (≈159.4 MPa), while Nb/Mo alloying enhanced solid-solution strengthening (≈302.5 MPa) in the FZ. • Inconel 625 filler increased the fusion zone strength (≈478 MPa yield stress) via solid-solution, mitigating softening due to grain coarsening.