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Herein, a combination of cold rolling (CR) and annealing treatment is used to investigate the evolution of the microstructure and mechanical properties of CoFeNiMnV high‐entropy alloys (HEAs) fabricated by powder plasma arc additive manufacturing (PPA‐AM). The deposited CoFeNiMnV HEAs exhibit a face‐centered cubic (FCC) structure with a small amoun...
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... Figure 3d compares our EHEAs to single-, multi-phased HEAs and EHEAs in the Al-Co-Cr-Fe-Ni family with regard to their strength and ductility (see Supplementary Table 1 for details). While thermomechanical processing of conventional metals leads to the trade-off between strength and ductility 37,38,46 , however, it is clear that our P2 EHEA is breaking this norm by delivering exceptional strengthductility combination when compared to other HEAs and EHEAs. Notably, further annealing led to degradation of both strength and ductility. ...
The well-known strength-toughness trade-off has long been an obstacle in the pursuit of advanced structural alloys. Here, we develop a eutectic high entropy alloy that effectively overcomes this limitation. Our alloy is composed of face-centered cubic and body-centered cubic crystalline phases, and demonstrates attractive mechanical properties by harnessing microstructural hybridization and a strain-induced phase transition between phases. Unlike conventional eutectic alloys, the compositionally complexity of our alloy allows control of its microstructural and chemical heterogeneities across multiple length scales, ranging from atomic- and nano-scales to meso-scales. Optimizing these microstructural and chemical heterogeneities within our alloy enables high strength and ductility because of enhanced fracture resistance, outperforming alternative high and medium entropy alloys with similar compositions and microstructures.
... The results indicate that increasing the Cr content in HEAs promotes the generation of metal compound σ-phase. According to the available experimental results, element V induces the generation of the σ-phase in HEAs, and the volume fraction and quantity of the σ-phase are proportional to the concentrations of Cr and V elements [49][50][51][52]. The above analysis determined that CoCr 0⋅25 FeNiMnV is the FCC phase, and CoCr x FeNiMnV (x = 0.5, 0.75, 1) is the FCC + IM phase. ...
... Additive manufacturing (AM) has the advantage of different energy sources, including laser, arc, plasma, and electron beams, to directly manufacture components and parts with complex geometries. Laser metal deposition (LMD) [8], selective laser melting (SLM) [9], wire arc additive manufacturing (WAAM) [10], plasma arc additive manufacturing (PAAM) [11,12], and selective electron beam melting (SEBM) [13] have been Additive manufacturing was performed using a five-axis hybrid additive -subtractive manufacturing machine (H320, Guangdong Additive and Subtractive Technology Co., Ltd., Foshan, China) integrated on a five-axis CNC machine with a coaxial powder-feeding direct laser deposition system and a 2000 W semiconductor fiber laser (RFL-2000-SM-ABP-R, RAYCUS manufacturing Technology Co., Ltd., Wuhan, China) with wavelength of 1.06 µm (Figure 1a). High-purity nitrogen was used as the shielding and powder-feeding gas to protect the molten pool from oxidation. ...
This work demonstrates the successful additive manufacturing of an in situ-alloyed CoCrFeNi HEA with a single phase (FCC) structure via the laser metal deposition (LMD) technique. In this work, bulk specimens of the CoCrFeNi high entropy alloy (HEA) of size 15 mm × 15 mm × 45 mm were additive-manufactured (AMed). An H320-type additive-subtractive manufacturing all-in-one system with a 2 kW fiber laser with a coaxial nozzle head integrated in a five-axis CNC machine was used. The effect of varying laser powers (1000 W, 1300 W, and 1600 W) on the microstructure and mechanical and electrochemical properties of the AMed HEA specimens was investigated. The AMed specimens were analyzed for their microstructure, elemental distributions, microhardness, and mechanical and electrochemical properties. An increase in the laser power led to a non-uniform cooling rate and non-steady solidification rates of the molten area during the AM process. As a result, the crystal constant decreased, and the microhardness fluctuated within a narrow range across the specimen. Among the three laser powers, the AMed CoCrFeNi HEA at 1300 W had the optimal mechanical properties and the best electrochemical behavior in 3.5 wt.% NaCl solution.
Herein, the L12‐strengthened Co34Cr32Ni27Al3.5Ti3.5 medium‐entropy alloy (MEA) with outstanding strength and ductility is developed through cold rolling and annealing (CRA). The CRA promotes the formation of coherent L12 nanoprecipitates in the matrix and precipitates inside the grains (Ti‐rich phases), resulting in dislocation sliding and multiplication during deformation. The as‐cast sample exhibits low yield strength (YS) of ≈498.5 MPa, ultimate tensile strength (UTS) of ≈820.5 MPa, and uniform elongation (UE) of ≈29.8%. After cold rolling and annealing, the YS, UTS, and UE are significantly increased to ≈678.4, ≈1109.3 MPa, and ≈44.5%, respectively. The excellent mechanical performance results from dislocation strengthening and precipitation strengthening of the L12 phase. The trade‐off of strength‐ductility is resolved by achieving an appropriate balance between the hard phase rich in L12/Ti and the soft face‐centered cubic phase. This finding demonstrates that the CRA method can be used to create coherent L12 nanoprecipitates that are beneficial for strong and ductile MEA. This work provides a broader perspective for CoCrNi‐based MEAs with high performance in the future.
The modern technical society aims to generate sustainable and reliable energy resources motivated by the energy-dense hydrogen (H2) economy. High entropy alloy (HEA) catalyst is a multi-metal composite that is considered as a key electrocatalytic material for superior electrochemical applications. However, the theoretical understanding and underlying mechanisms of the superior electrocatalytic activity of HEA are still unclear and largely unexplored. In this short review, we briefly discuss the theoretical and experimental aspects of HEA catalysts, followed by the importance of HEA catalysts in electrocatalytic hydrogen production. Finally, we propose some perspectives for the structural and electrochemical analysis of HEA catalysts for performance improvement and integration with other potential applications.
