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High entropy alloys (HEAs) are a novel class of materials that represent an evolution of common engineering alloys to a wider array of compositional and properties possibilities. As such, the exploration of methodologies to achieve improved microstructure and mechanical characteristics of these materials for potential applications in industry is a requirement that is experiencing extended research efforts. One example of a processing method able to expand the potential applications of these alloys is Gas Tungsten Arc Welding (GTAW), which allows to evaluate the metallurgical evolution and corresponding mechanical performance, associated to the impact of a localized heat input on the material. However, GTAW and related fusion-based welding processes are known to generate large grain sized-structures in the fusion zone, which often is detrimental to the joint performance. Thus, the integration of high temperature inoculant particles on the fusion zone during welding is a potential way to improve this region's microstructure and, therefore, its mechanical performance. In this work, we discuss the effect that the addition of TiB 2 micron-sized particles have on the microstructure of a GTAW AlCoCrFeNi-based HEA. For this, the microstructure of the welds was evaluated by means of optical and electron microscopy, synchrotron X-ray diffraction and CalPhaD-based simulations. Mechanical testing was performed using microhardness mapping and tensile testing coupled with digital image correlation. The results evidenced that successful inoculation with TiB 2 proved capable of altering the microstructure of the fusion zone (FZ), refining it. Nevertheless, preferential deformation in the relatively softer heat affected zone during tensile testing resulted on premature failure of the inoculated joints, due to the concomitant higher hardness of the FZ. [Display omitted] • Gas tungsten arc welding was successfully used for joining an AlCoCrFeNi high entropy alloy. • Addition of TiB 2 to the fusion zone influenced grain structure and local mechanical properties. • Microstructure and mechanical characterization aided by thermodynamic modelling unveil the role of TiB 2 particles. • Mechanical properties of AlCoCrFeNi joints depends on the selection of inoculant particles and fraction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optimal annealing temperatures for GMAWed CoCrFeMnNi joints with 410 stainless filler were determined through high-throughput thermodynamic calculations. • BM and HAZ phases match model predictions, slight FZ deviations observed. • FZ precipitates had no detrimental effect on joint mechanical properties. • PWHT boosts joint plasticity by ≈7 sevenfold (43.1 % vs. 6.4 %) while maintaining strength (587 vs. 641 MPa). • Tensile failure shifts from weld toe to BM zone after annealing. Post-weld annealing is a promising method for enhancing the performance of welded joints. However, traditional trial-and-error approaches are often time-consuming and inefficient, limiting their application in industrial production. To overcome this challenge, this study integrates high-throughput thermodynamic simulation techniques with a custom Python script to rapidly screen annealing temperatures for GMAWed CoCrFeMnNi high entropy alloy welded joints with ERNiMo-410 filler wire. By employing a combination of microstructural characterizations (such as Electron Backscatter Diffraction (EBSD) and Synchrotron X-ray Diffraction (SXRD)) and mechanical testing (including hardness testing and tensile Digital Image Correlation (DIC) analysis), the study validates the effects of selected annealing temperatures on the microstructure evolution and mechanical behavior of the welded joints. The results demonstrate that the optimized annealing temperature significantly enhances the uniformity of the microstructure and increases elongation at fracture by approximately sevenfold to 43.1 %, while maintaining comparable yield and ultimate strengths. This study highlights the potential industrial value of this method, offering an efficient and scientific approach for optimizing welded joint performance. [ABSTRACT FROM AUTHOR]

In this paper, gas metal arc welding of a CoCrFeMnNi high entropy alloy was performed using 308 stainless steel filler wire. Electron backscatter diffraction and synchrotron X-ray diffraction were used to determine the microstructural evolution, while microhardness mapping and non-contact digital image correlation were employed to assess the local mechanical response across the welded joints. Further, thermodynamic calculations were implemented to support the understanding of the microstructure evolution. Through a systematic analysis of the microstructure evolution and mechanical properties, it is established a correlation between welding process, microstructure and mechanical properties. Besides, this work lays the foundations for the use of low-cost arc-based welding technologies for successful joining and application of welded joints based on high entropy alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Gas tungsten arc welding was used to join an as-cast AlCoCrFeNi 2.1 eutectic high entropy alloy. • No welding defects were observed. • Synchrotron X-ray diffraction, electron microscopy and thermodynamic calculations used to evaluate the joint microstructure. • The fusion zone exhibits the highest hardness due to a refined interlamellar thickness. • The welded joints present a good strength/ductility balance. The AlCoCrFeNi 2.1 eutectic high entropy alloy is of great interest due to its unique mechanical properties combining both high strength and plasticity. Here, gas tungsten arc welding was performed for the first time on an as-cast AlCoCrFeNi 2.1 alloy. The microstructural evolution of the welded joints was assessed by combining electron microscopy with electron backscatter diffraction, synchrotron X-ray diffraction analysis and thermodynamic calculations. Microhardness mapping and tensile testing coupled with digital image correlation were used to investigate the strength distribution across the joint. The base material, heat affected zone and fusion zone are composed of an FCC + B2 BCC eutectic structure, although the relative volume fractions vary across the joint owing to the weld thermal cycle. The BCC nanoprecipitates that existed in the base material started to dissolve into the matrix in the heat affected zone and closer to the fusion zone boundary. Compared to the as-cast base material, the fusion zone evidenced grain refinement owing to the higher cooling rate experienced during solidification. This translates into an increased hardness in this region. The joints exhibit good strength/ductility balance with failure occurring in the base material. This work establishes the potential for using arc-based welding for joining eutectic high entropy alloys. [ABSTRACT FROM AUTHOR]

The use of filler materials during fusion-based welding processes is widely used to regulate and modify the composition of the welded joints aiming at producing a desired microstructure and/or achieving an improvement in its mechanical performance. Welding of high entropy alloys is still a new topic and the impact of different filler materials on the microstructure and mechanical properties is yet unknown. In this work, gas metal arc welding of the CoCrFeMnNi high entropy alloy using 410 stainless steel as a filler wire was performed. The microstructural evolution of the welded joints was evaluated by optical microscopy, scanning electron microscopy aided by electron backscattered diffraction, high energy synchrotron X-ray diffraction and thermodynamic calculations. Meanwhile, the mechanical behavior of the welded joint, as well as the local mechanical response were investigated with microhardness mapping measurements and with non-contact digital image correlation during tensile loading to failure. The weld thermal cycle promoted solid state reactions in the heat affected zone (recovery, recrystallization and grain growth), which impacted the microhardness across the joint. The role of the 410 stainless steel filler material in the solidification path experienced by the fusion zone was evaluated using Scheil-Gulliver calculations, and a good agreement with the experimentally observed phases was observed. Despite the addition of the 410 stainless steel filler was not conducive to an increase in the fusion zone hardness, the associated bead reinforcement promoted an improvement in both the yield and tensile strengths of the joint compared to a similar weld obtained without filler material (355 vs 284 MPa and 641 vs 519 MPa, respectively). This allows to infer that the addition of filler materials for welding high entropy alloys is a viable method for the widespread use of these novel materials. In this work, by coupling microstructure and mechanical property characterization, a correlation between the processing conditions, microstructure and mechanical properties was obtained providing a wider basis for promoting the application of gas metal arc welding of high entropy alloys for industrial applications. [Display omitted] • Gas metal arc welding using 410 stainless steel filler wire to join a CoCrFeMnNi high entropy alloy was performed. • Recrystallization followed by grain growth were the primary causes behind heat affected zone softening. • Existing phases predicted by thermodynamic calculations were in good agreement with those observed at the fusion zone. • Stress concentration at the weld toe is a dominant factor contributing to failure of welded joints. • Suitability of using filler materials for joining CoCrFeMnNi high entropy alloys is demonstrated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Laser welding between a CoCrFeMnNi high entropy alloy and 316 stainless steel was performed. • Joint ductility increased from 5 to 10 % by changing the CoCrFeMnNi high entropy alloy from rolled to annealed condition. • The joints strength is preserved at ≈ 450 MPa regardless of the CoCrFeMnNi high entropy alloy condition. • The CoCrFeMnNi / 316 stainless steel joints can be considered for structural applications. Dissimilar joining involving high entropy alloys is currently being explored to evaluate the suitability of these novel advanced engineering materials in structural applications. Recently, joining of a CoCrFeMnNi high entropy alloy to 316 stainless steel was successfully attempted. However, the joint ductility was limited by the lack of deformation experienced by the cold-rolled CoCrFeMnNi base material during tensile loading. In this work, it is shown that by simply changing the base material condition, from cold-rolled to annealed, it is possible to significantly improve the joint fracture strain from ≈ 5 to ≈ 10 %, while preserving the strength at ≈ 450 MPa. Using electron microscopy, high energy synchrotron X-ray diffraction and mechanical testing aided by digital image correlation, the microstructure evolution across the welded joint is assessed and correlated to its mechanical performance. Moreover, thermodynamic calculations considering the compositional changes across the fusion zone were used to predict the microstructure evolution of this region. [ABSTRACT FROM AUTHOR]