A new pseudo binary strategy to design eutectic high entropy alloys using mixing enthalpy and valence electron concentration

A new CrFeNi2Al eutectic high entropy alloy system with excellent mechanical properties

Eutectic high‐entropy alloys (EHEAs), as an important branch of high‐entropy alloys (HEAs), have become hotpots in the materials field due to the excellent combination of mechanical properties and casting liquidity. However, designing of EHEAs containing nonmetallic elements has been rarely reported. Herein, a new strategy to design EHEAs containing nonmetallic elements by introducing an idealized mode of A‐(M + N) and using computer‐aided thermodynamic calculations is proposed. Based on this strategy, four new EHEAs, namely, CoFeNi2–Ti0.48Si0.8, CoCrNi2–V0.86B0.43, CoCrFeNi2–V0.89B0.45Si0.15, and CoCrNi2–MoC0.6, are designed and prepared. The CoFeNi2–Ti0.48Si0.8 and CoCrNi2–MoC0.6 EHEAs are composed of face‐centered‐cubic (FCC) + M16Ti6Si7‐type silicide and FCC + M23C6 + M6C‐type carbide, respectively. The CoCrNi2‐V0.86B0.43 and CoCrFeNi2‐V0.89B0.45Si0.15 EHEAs exhibit the same eutectic microstructure as FCC + M3B2‐type boride. The synthesized EHEAs containing nonmetallic elements show excellent mechanical properties. The experimental result indicates that this strategy can provide a feasible and effective way to develop new EHEAs with nonmetallic elements.

Corrosion behaviors and passive film properties of a newly developed cost-effective AlCrFeNi eutectic high entropy alloy in different corrosive solutions

A novel corrosion resistant NiFeCrAlTi eutectic high entropy alloy with high strength and ductility

Ultra strong and ductile eutectic high entropy alloy fabricated by selective laser melting

Enhanced strength and ductility of Al0.9CoCrNi2.1 eutectic high entropy alloy by thermomechanical processing

Eutectic high-entropy alloys (EHEAs), such as nano-lamellar AlCoCrFeNi₂.₁, have gained widespread attention due to their excellent mechanical properties, high hardness, wear resistance, and corrosion resistance—even at elevated temperatures (e.g., >1000 °C). In this study, we investigated the corrosion behavior of AlCoCrFeNi₂.₁ EHEAs fabricated via laser powder bed fusion (L-PBF) 3D printing, as a function of annealing temperature.These EHEAs are composed of two phases: a ductile FCC L1₂ phase and a high-strength BCC B2 phase. Due to the rapid solidification inherent to L-PBF, the as-printed microstructure is far from equilibrium, resulting in a nearly homogeneous elemental distribution across phases. Upon annealing, the system evolves toward equilibrium, leading to enrichment of Cr, Co, and Fe in the FCC phase and Al and Ni in the BCC phase. Additionally, because Cr has limited solubility in the B2 phase, Cr-rich precipitates (on the order of tens of nanometers) form and become more prominent with higher annealing temperatures. Three processing conditions were considered in this study: (1) as printed, (2) annealed at 600 °C for 5 hours, and (3) annealed at 1000 °C for 1 hour. With increasing annealing temperature, the lamellar B2 phase coarsened, Cr-rich precipitates grew, and elemental segregation became more pronounced. Samples were characterized using electron backscatter diffraction to determine crystallographic orientation and energy-dispersive spectroscopy to assess local composition.Further, in situ electrochemical Atomic Force Microscopy was deployed to investigate the relationship between microstructure and corrosion behavior. These studies revealed preferential corrosion of the B2 phase and was most pronounced in regions adjacent to Cr-rich precipitates, where the matrix is depleted in Cr. Corrosion was found to be greater in samples subject to increased annealing temperature. For instance, after 5 hours exposure in 0.05 M H2SO4, corrosion pit depths increased from ~ 10 nm in the as-printed structure to ~360 nm on the sample annealed at 1000°C, while the pitted area increased from ~2% to 12%.Additionally, electrochemical impedance spectroscopy was used to quantify the charge transfer resistance-an indicator inversely proportional to the corrosion rate- and to monitor oxide evolution. Laser confocal microscopy was used to assess corrosion over larger areas and extended time scales. We expect that such a multimodal approach will inform processing methodologies to design materials systems for high mechanical performance and robust corrosion resistance. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Understanding microstructure and mechanical properties of (AlTa0.76)xCoCrFeNi2.1 eutectic high entropy alloys via thermo-physical parameters

Enhanced strength and ductility in a brittle hypoeutectic high-entropy alloy via spheroidizing annealing

Fabricating eutectic high-entropy alloys (EHEAs) via selective laser melting (SLM) presents significant potential for advanced structural applications. This study explores the microstructural evolution of Fe32Cr33Ni29Al3Ti3 EHEAs fabricated by SLM under varying laser powers. Electron backscatter diffraction (EBSD) analysis revealed that samples fabricated at 200 W exhibited approximately 70% face-centered-cubic (FCC) and 30% body-centered-cubic (BCC) phases. In comparison, those processed at 160 W showed an increased FCC fraction of 85% with a corresponding reduction in BCC content. Grain size measurements indicated that BCC grains were consistently finer than their FCC counterparts. Thermal simulations demonstrated that higher laser power produced deeper melt pools and broader temperature gradients. By correlating thermal history with phase diagram data, the spatial variation in BCC content was attributed to the differential residence time in the 1350–1100 °C range. This study represents one of the first attempts to quantitatively link local thermal histories with the evolution of dual-phase (FCC + BCC) microstructures in EHEAs during SLM. The findings contribute to the improved understanding and control of phase formation in complex alloy systems, providing valuable guidance for tailoring SLM parameters to optimize the phase composition and microstructure of EHEAs.

New insight into tailorable eutectic high entropy alloys with remarkable strength–ductility synergy and ample shaping freedom fabricated using laser powder bed fusion

Dissimilar fusion welding between NiTi shape memory alloy and AlCoCrFeNi 2.1 , eutectic high entropy alloy was achieved using a combination of Nb and Cu interlayers. Both base metals exhibit unique properties that complement each other making them attractive for integration in smart systems. However, direct joining of these materials is not feasible due to the formation of brittle intermetallic compounds that compromise the joint integrity. Thus, to avoid this metallurgical issue dissolution of the Nb and Cu interlayers promoted elemental intermixing and altered solidification pathways, leading to the formation and intensification of topologically close-packed phases. Phase evolution was assessed through thermodynamic CALPHAD simulations and validated using synchrotron X-ray diffraction, while further microstructural characterization employed backscattered electron imaging and energy dispersive spectroscopy. The weld exhibited pronounced spatial heterogeneity, with a peak hardness of 856 HV 0.3 near the NiTi-side interfacial region, consistent with enrichment of TCP phases and Ti-rich intermetallics. Tensile testing showed fracture at an ultimate tensile strength of 372 MPa and a fracture strain of 1.11%, with crack initiation in the hardened interfacial region followed by mixed-mode fracture toward the fusion zone. Although tensile ductility remains limited, the multi-interlayer strategy enabled defect-free joint formation and confined embrittlement to a narrow region compared with direct joining. • Fusion welding of NiTi shape memory alloy with AlCoCrFeNi 2.1 eutectic high entropy alloy is investigated using multiple interlayers to minimize intermetallic formation. • Interlayer dissolution produced a heterogeneous microstructure, promoting the formation of topologically close-packed phases that influenced the mechanical behaviour of the joint. • CALPHAD simulations and synchrotron X-ray diffraction revealed the impact of elemental intermixing and phase evolution across the composite weld zone.

Phase selection and mechanical properties of directionally solidified AlCoCrFeNi2.1 eutectic high-entropy alloy

Alloy design of Cr-Co-Ni-Ta eutectic medium entropy alloys (EMEAs) was performed through a CALPHAD method coupled with experimental study, with the aim to attain high phase stability as well as excellent mechanical properties. Based on calculated pseudo-binary diagram, CrCoNiTax (x = 0.1, 0.3, 0.4, 0.5, 0.7) medium entropy alloys were investigated. Two phases, FCC solid solution and Laves phase, were identified in the alloys. With increasing Ta content, the volume fraction of hard and brittle Laves phase increased, microstructure changed from hypoeutectic (Ta0.1, Ta0.3) to eutectic (Ta0.4) and then to hypereutectic (Ta0.5, Ta0.7). The stability of phases was assessed by considering the thermodynamic parameter Ω and valence electron concentration (VEC). The eutectic phases become stable when 1.42 < Ω < 0.74 and 7.5 < VEC < 8.25. In addition, based on nanoindentation, the results indicated that solid solution strengthening in γ phase was significantly enhanced, eutectic phase in CrCoNiTa0.4 EMEA was found to process the highest microhardness and elastic modulus. Finally, the hardness of alloys was positively correlated with the content of Ta and the plastic strain of alloys obviously decreased, while the compression strength firstly increased and then decreased. CrCoNiTa0.4 was the most promising alloy with the highest compression strength (2502 MPa) and high plastic strain (20.6%).

Hetero-deformation promoted strengthening and toughening in BCC rich eutectic and near eutectic high entropy alloys