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Liquid metal embrittlement (LME) is a longstanding problem for resistance spot welding (RSW) of Zn-coated automotive sheet steels, especially third generation advanced high-strength steels (AHSSs). This work designed a multi-principal element alloy (MPEA), considered a high entropy alloy (HEA), that preferentially absorbs Zn during RSW and forms a single solid solution phase. The MPEA composition was designed using a highthroughput multi-physics-based analysis, which down-selected the FeMnNiCoZn system as favorable to present a single face-centered cubic (FCC) phase over a broad dilution composition space with the substrate. Comparing the welds made with MPEA foils to control welds without the MPEA, optical microscopy revealed no visible LME cracks in MPEA welds, whereas Zn-lined cracks with a length of 5–100 μm populated the control welds. Energydispersive spectroscopy demonstrated the MPEAlimited Zn penetration distance into the AHSS grain boundaries to less than 10 μm. Kinetic simulations also predicted the MPEA would retain Zn as a solid solution and limit its penetration into the AHSS substrate. Site-specific synchrotron diffraction confirmed a single FCC phase in the MPEA and an unaffected ferrite/martensite microstructure in the adjacent DP980 AHSS substrate. Furthermore, tensile-shear tests showed average improvements of 21% in peak load and 80% in fracture energy in welds employing MPEA foils when welded with the same current and schedule. 

The performance of a newly developed multiprincipal-element alloy (MPEA) filler metal for brazing of nickel-based superalloys was directly compared to a conventional boron- and silicon-suppressed filler (BSSF) metal. The comparison was demonstrated on an Alloy 600 substrate with a brazing temperature of 1200°C. Single-phase solidification behavior and the absence of boron and silicon in the MPEA led to a joint microstructure devoid of eutectic constituents or brittle phases in brazes employing this filler metal. In the brazes using the conventional BSSF metal, incomplete isothermal solidification and subsequent athermal solidification of the residual liquid resulted in large particles of a chromium-rich boride phase distributed throughout the microstructure. Tensile testing of brazed butt joints at both room temperature and 600°C testing conditions demonstrated that the MPEA joints exhibited total ductility values at least one order of magnitude greater than that of BSSF joints, but they showed comparable yield strengths in both testing conditions. Fractographic assessment confirmed that boride phases nucleated cracks and resulted in brittle failure in the BSSF joints, while the MPEA joints exhibited extensive ductile microvoid coalescence. Fine-scale porosity and oxide inclusions may be the dominant factors limiting the overall ductility observed in the MPEA brazes. 

Abstract The solidification mechanism and segregation behavior of laser-melted Mn₃₅Fe₅Co₂₀Ni₂₀Cu₂₀was firstly investigated via in situ synchrotron x-ray diffraction at millisecond temporal resolution. The transient composition evolution of the random solid solution during sequential solidification of dendritic and interdendritic regions complicates the analysis of synchrotron diffraction data via any single conventional tool, such as Rietveld refinement. Therefore, a novel approach combining a hard-sphere approximation model, thermodynamic simulation, thermal expansion measurement and microstructural characterization was developed to assist in a fundamental understanding of the evolution of local composition, lattice parameter, and dendrite volume fraction corresponding to the diffraction data. This methodology yields self-consistent results across different methods. Via this approach, four distinct stages were identified, including: (I) FCC dendrite solidification, (II) solidification of FCC interdendritic region, (III) solid-state interdiffusion and (IV) final cooling with marginal diffusion. It was found out that in Stage I, Cu and Mn were rejected into liquid as Mn₃₅Fe₅Co₂₀Ni₂₀Cu₂₀solidified dendritically. During Stage II, the lattice parameter disparity between dendrite and interdendritic region escalated as Cu and Mn continued segregating into the interdendritic region. After complete solidification, during Stage III, the lattice parameter disparity gradually decreases, demonstrating a degree of composition homogenization. The volume fraction of dendrites slightly grew from 58.3 to 65.5%, based on the evolving composition profile across a dendrite/interdendritic interface in diffusion calculations. Postmortem metallography further confirmed that dendrites have a volume fraction of 64.7% ± 5.3% in the final microstructure. 

The microstructural and mechanical properties of a MnFeCoNiCu braze filler are analyzed and compared to a conventional nickel‐based braze filler alloy on Haynes 214 as the base material. Tensile tests reveal that the samples brazed with the MnFeCoNiCu compositionally complex alloy (CCA) exhibit superior ductility increased by a factor of 1.6 compared to those brazed with the nickel‐based filler. The ultimate tensile strength remains comparable (factor 1.03). Contact angles recorded during the brazing process indicate comparable wetting properties between the two fillers. Based on experimental investigations and Thermo–Calc predictions, improved brazing parameters are proposed for the CCA filler on Haynes 214. These recommendations include lower brazing temperatures, shortened holding times, and faster cooling rates.