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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]

• In-situ tensile testing is performed up to failure under synchrotron X-ray diffraction. • Stress/strain level dependent strengthening mechanisms are exhibited in terms of diffraction peaks change. • The microstructure evolution, phase transformation, and strengthening mechanisms occurring during loading on a dual-phase high entropy alloy are detailed. The present research focuses on analyzing the deformation mechanisms associated with tensile loading of the Fe 50 Mn 30 Co 10 Cr 10 high entropy alloy (HEA) using synchrotron x-ray diffraction (SXRD). This novel material is comprised by two major phases: γ-FCC and ε-HCP, where transformation induced plasticity (TRIP) effectively transforms the first into the latter, upon the application of an external stress. However, the presence of thermally stable ε-HCP prior to loading will also influence the deformation mechanism of the material during mechanical solicitation. As such, here we investigate the activation of different strain accommodation mechanisms and the consequent microstructural evolution. Four stages were identified in the mechanical response of this novel HEA, where the TRIP and the twinning induced plasticity (TWIP) deformation modes are the main events granting this HEA its outstanding properties. Such sequence of events allows to evidence the effectiveness of the collaboration between the transformative capability of the γ-FCC phase and the work hardening potential of the ε-HCP phase. This analysis is performed via quantitative and qualitative analysis of the SXRD data, allowing also to investigate the response behavior of specific crystallographic planes to the increasing stress throughout the experiment. [Display omitted] [ABSTRACT FROM AUTHOR]

In recent years, high entropy alloys (HEAs) have been shown to be promising alternatives to common engineering alloys, depending on their composition and thermomechanical processing. Up to now, several works aimed at improving the mechanical properties and discovering different HEAs given the extremely large compositional possibilities made available by the multicomponent approach associated to these materials. Their processability, however, is an important topic that must be studied. Welding is a key manufacturing technique that will eventually be applied to HEAs. Thus, there is a need to evaluate the microstructure and property changes induced by the weld thermal cycles, to assess the suitability of certain welding process/HEAs combinations for possible industrial applications. In the present work, Gas Tungsten Arc Welding (GTAW) was used to achieve defect-free joints based on a novel transformation induced plasticity (TRIP) Fe 50 Mn 30 Co 10 Cr 10 HEA. The microstructure and mechanical behavior of the joints were assessed by means of optical and electron microscopy, synchrotron X-ray diffraction, thermodynamical calculations, microhardness mapping and tensile testing. Overall, an excellent mechanical performance was obtained on the resulting joints, opening the door for their adoption in real-life applications. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • In-situ synchrotron X-ray diffraction and electron backscattered diffraction are used during tensile testing to failure. • Microstructure evolution, phase transformation and strengthening mechanisms of a metastable high entropy alloy is detailed. • Different deformation and strengthening mechanisms are dependent on the applied stress/strain. In this work, a combination of in-situ high synchrotron X-ray diffraction and electron backscattered diffraction were used to systematically investigate the activation and evolution of the deformation mechanisms in an as-cast Fe 42 Mn 28 Co 10 Cr 15 Si 5 metastable high entropy alloy deformed until fracture at room temperature. This work unveils the critical role of the dual-phase γ-f.c.c. / ε-h.c.p. microstructure on the deformation response of the alloy. The different deformation modes, i.e., slip, transformation induced plasticity (TRIP) and transformation induced twinning (TWIP), were seen to initiate at different loading stresses and then to overlap. Quantitative microstructural characterization, which included the evolution of the phase fraction, stress partitioning, dislocation density, c/a ratio and lattice strain for different planes, was performed to elucidate the role of each phase on the macroscopic mechanical response of the metastable high entropy alloy. Furthermore, the magnitude of the different strengthening contributions has been quantified for the first time. [ABSTRACT FROM AUTHOR]

Weldability studies on high entropy alloys are still relatively scarce, delaying the deployment of these materials into real-life applications. Thus, there is an urgent need for in-depth studies of the weldability of these novel advanced engineering alloys. In the current work, an as-cast Fe 42 Mn 28 Co 10 Cr 15 Si 5 metastable high entropy alloy was welded for the first time using gas tungsten arc welding. The weld thermal cycle effect on the microstructure evolution over the welded joint was examined using electron microscopy in combination with electron backscatter diffraction, synchrotron X-ray diffraction analysis, and thermodynamic calculations. Furthermore, tensile testing and hardness mapping were correlated with the microstructure evolution. The microstructure evolution across the joint is unveiled, including the origin of the ε-h.c.p. phase at different locations of the material. Different strengthening effects measured throughout the joint are associated with the weld thermal cycle and resulting microstructure. A synergistic effect of smaller grain size of the ε-h.c.p. phase in the fusion zone, overturns the reduced volume fraction of this phase, increasing the local strength of the material. Moreover, the brittle nanosized σ phase was also found to play a critical role in the joints' premature failure during mechanical testing. [Display omitted] • Welding with gas tungsten arc has been successfully performed for the first time on Fe 42 Mn 28 Co 10 Cr 15 Si 5 metastable high entropy alloys. • Joints with good mechanical properties were obtained. • The heat affected zone undergoes the γ-f.c.c. to ε-h.c.p. martensitic phase transformation driven by a competition between grain size, local peak temperature and cooling rate. • A larger volume fraction of hard σ phase distributed in the fusion zonecontributes to failure of the welded joints. [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]

[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]

High entropy alloys have emerged as novel engineering alloys with remarkable mechanical properties in a wide range of temperatures. Among the several high entropy alloys that were already described, the equiatomic CrMnFeCoNi alloy is the most studied one. In this work, gas tungsten arc welding of as-rolled CrMnFeCoNi high entropy alloy sheets was performed. The microstructural characterization encompassed the use of electron microscopy, including electron backscattered diffraction, synchrotron X-ray diffraction analysis, microhardness testing and mechanical evaluation. A comprehensive description of the microstructural evolution, including texture and microstrain determination, of the joint is presented and discussed. Upon mechanical testing, the joints systematically failed in the fusion zone due. The large grain size and low hardness of this region justifies the failure location. The joints' mechanical behaviour is correlated with the material microstructure. Unlabelled Image • Gas tungsten arc welding of as-rolled CrMnFeCoNi high entropy alloys is performed. • Defect-free joints with good mechanical behaviour were obtained. • Synchrotron X-ray diffraction was used to study the texture and microstrain along the joint. • Arc-based welding techniques are suitable for welding these novel advanced engineering alloys. [ABSTRACT FROM AUTHOR]