In this study, a new Al0.9CoFeNi2 eutectic high entropy alloy (EHEA) was designed, and the microstructures as well as the deformation behavior were investigated. The bulk cast Al0.9CoFeNi2 EHEA ...exhibited an order face-centered cubic FCC (L12) and an order body-centered cubic (B2) dual-phase lamellar eutectic microstructure. The volume fractions of FCC (L12) and B2 phases are measured to be 60 % and 40 %, respectively. The combination of the soft and ductile FCC (L12) phase together with the hard B2 phase resulted in superior strength of 1005 MPa and ductility as high as 6.2 % in tension at room temperature. The Al0.9CoFeNi2 EHEA exhibited obvious three-stage work hardening characteristics and high work-hardening ability. The evolving dislocation substructures during uniaxial tensile deformation found that planar slip dominates in both FCC (L12) and B2 phases, and the FCC (L12) phase is easier to deform than the B2 phase. The post-deformation transmission electron microscopy revealed that the sub-structural evolution of the FCC (L12) phase is from planar dislocations to bending dislocations, high-density dislocations, dislocation network, and then to dislocation walls, and Taylor lattices, while the sub-structural evolution of the B2 phase is from a very small number of short dislocations to a number of planar dislocations. Moreover, obvious ductile fracture in the FCC (L12) phase and a brittle-like fracture in the B2 phase were observed on the fracture surface of the Al0.9CoFeNi2 EHEA. The research results provide some insight into the microstructure-property relationship.
Eutectic high-entropy alloys (EHEAs), as a sub-group of high-entropy alloys (HEAs), are becoming a new research hotspot in the metallic materials community because of their excellent castability, ...fine and uniform microstructures even in the as-cast state, high strength, and good ductility. Some of the EHEAs have shown promising potentials for industrial applications. Here, the history, interesting solidification microstructure and mechanical properties, and the design strategy of EHEAs are reviewed, and their future prospects are outlined.
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Recent studies indicate that eutectic high-entropy alloys can simultaneously possess high strength and high ductility, which have potential applications in industrial fields. Nevertheless, ...microstructural origins of the excellent strength–ductility combination remain unclear. In this study, an AlCoCrFeNi2.1 eutectic high-entropy alloy was prepared with face-centered cubic (FCC)(L12)/body-centered-cubic (BCC)(B2) modulated lamellar structures and a remarkable combination of ultimate tensile strength (1351 MPa) and ductility (15.4%) using the classical casting technique. Post-deformation transmission electron microscopy revealed that the FCC(L12) phase was deformed in a matter of planar dislocation slip, with a slip system of {111} , and stacking faults due to low stacking fault energy. Due to extreme solute drag, high densities of dislocations are distributed homogeneously at {111} slip plane. In the BCC(B2) phase, some dislocations exist on two {110} slip bands. The atom probe tomography analysis revealed a high density of Cr-enriched nano-precipitates, which strengthened the BCC(B2) phase by Orowan mechanisms. Fracture surface observation revealed a ductile fracture in the FCC(L12) phase and a brittle-like fracture in the BCC(B2) lamella. The underlying mechanism for the high strength and high ductility of AlCoCrFeNi2.1 eutectic high-entropy alloy was finally analyzed based on the coupling between the ductile FCC(L12) and brittle BCC(B2) phases.
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Although eutectic high entropy alloys (EHEAs) display homogeneously fine microstructure, excellent castability and promising industrial application potential, how to design eutectic compositions in ...high entropy alloys (HEAs) remains to be challenging. Here, a novel strategy, specifically, through calculation of mixing enthalpy, was used to locate eutectic compositions in HEAs. As a proof of this concept, a series of EHEAs were located and prepared following the mixing enthalpy method. Using this new strategy, eutectic compositions can be designed conveniently, once one can classify elements into two different groups. This new alloy design strategy can be readily adapted to locate new EHEAs.
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•A new strategy to design eutectic high-entropy alloys was proposed using mixing enthalpy method.•A series of eutectic high-entropy alloys were located and prepared following the method.•Using this new strategy, eutectic compositions can be designed conveniently.
Second phase strengthening has been applied to high entropy alloys (HEAs) for optimizing mechanical properties. In this study, by conducting mechanical testing of a eutectic dual-phase AlCoCrFeNi HEA ...with homogenous distribution of body-centered cubic (BCC) and face-centered cubic (FCC) lamellar phases inside a transmission electron microscope, we found that although BCC was truly the hard phase, decreasing the proportion of BCC phase in fact increased the strength due to the existence of chemically disordered semi-coherent phase boundaries, which acted as potent impediments to dislocation motion resulting in dense dislocation storage in FCC phases. Moreover, the difficulty in dislocation glide caused massive cross-slip, and the interaction between primary slip arrays and cross-slip systems during deformation increased the rate of dislocation accumulation by forming dislocation substructures, thus making the FCC phases exceptionally strong. Our findings not only revealed the underlying strengthening mechanism of eutectic dual-phase AlCoCrFeNi HEAs, but also shed light on new ways in further optimizing the mechanical properties of HEAs.
•The AlCrFeNiMo0.2 alloy was solidified at a relatively low cooling rate.•Its fracture strength and plastic strain are 3222MPa, 0.287, respectively.•The FeCrMo-type σ phase is observed as a matrix ...phase.
The AlCrFeNiMox (x=0, 0.2, 0.5, 0.8, 1.0) high entropy alloys were produced by vacuum arc melting, and their microstructure and mechanical properties were investigated. AlCrFeNi, AlCrFeNiMo0.2, and AlCrFeNiMo0.5 alloys contained two body centered cubic (BCC) phases which were AlNi-type intermetallic compound and FeCr-type solid solution. The diffraction peaks of the two BCC phases separated with the increase of Mo content while Mo element preferred to dissolve into FeCr-type solid solution. When the value of x was higher than 0.5, the FeCrMo-type σ phase appeared and replaced the FeCr-type solid solution. The AlCrFeNiMo0.2 had the highest fracture strength of 3222MPa and plastic strain of 0.287. The hardness increased obviously from HV472.4 to HV911.5 with the addition of Mo element. The solid-solution strengthening of the BCC matrix and the σ phase hardening were the two main factors that strengthened the alloys. The AlCrFeNiMo0.2 high entropy alloy possesses the excellent mechanical properties which imply its potential application in industrial areas.
Increasing evidence supported the possible neuro-invasion potential of SARS-CoV-2. However, no studies were conducted to explore the existence of the micro-structural changes in the central nervous ...system after infection. We aimed to identify the existence of potential brain micro-structural changes related to SARS-CoV-2.
In this prospective study, diffusion tensor imaging (DTI) and 3D high-resolution T1WI sequences were acquired in 60 recovered COVID-19 patients (56.67% male; age: 44.10 ± 16.00) and 39 age- and sex-matched non-COVID-19 controls (56.41% male; age: 45.88 ± 13.90). Registered fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were quantified for DTI, and an index score system was introduced. Regional volumes derived from Voxel-based Morphometry (VBM) and DTI metrics were compared using analysis of covariance (ANCOVA). Two sample t-test and Spearman correlation were conducted to assess the relationships among imaging indices, index scores and clinical information.
In this follow-up stage, neurological symptoms were presented in 55% COVID-19 patients. COVID-19 patients had statistically significantly higher bilateral gray matter volumes (GMV) in olfactory cortices, hippocampi, insulas, left Rolandic operculum, left Heschl's gyrus and right cingulate gyrus and a general decline of MD, AD, RD accompanied with an increase of FA in white matter, especially AD in the right CR, EC and SFF, and MD in SFF compared with non-COVID-19 volunteers (corrected p value <0.05). Global GMV, GMVs in left Rolandic operculum, right cingulate, bilateral hippocampi, left Heschl's gyrus, and Global MD of WM were found to correlate with memory loss (p value <0.05). GMVs in the right cingulate gyrus and left hippocampus were related to smell loss (p value <0.05). MD-GM score, global GMV, and GMV in right cingulate gyrus were correlated with LDH level (p value <0.05).
Study findings revealed possible disruption to micro-structural and functional brain integrity in the recovery stages of COVID-19, suggesting the long-term consequences of SARS-CoV-2.
Shanghai Natural Science Foundation, Youth Program of National Natural Science Foundation of China, Shanghai Sailing Program, Shanghai Science and Technology Development, Shanghai Municipal Science and Technology Major Project and ZJ Lab.
Topologically close-packed (TCP) phases with complex structures are often observed in high entropy alloys (HEAs). Currently, these TCP phases are garnering significant interest from both theoretical ...and experimental perspectives due to the ductility deterioration of the high strength HEAs. Alternatively, there are instances when TCP phases can actually benefit the mechanical performances of alloys, such as the wear resistance. Therefore, the stability of TCP phases should be taken into consideration in the alloy design. In this paper, the relationship between the TCP phase stability and the physicochemical/thermodynamic properties of alloying components in HEAs was systematically studied. The stability of TCP phases was found to correlate well with the electro-negativity difference (DeltaX) for most of the reported HEAs. The stability of TCP phases is well delineated by the electro-negativity difference (DeltaX): i.e., TCP phases are stable at DeltaX > 0.133 except for some HEAs that contain a significant amount of aluminum.
The effects of C element on the microstructure and properties of CoCrFeNiC,. high entropy alloys （x denoted the atomic fraction of C element at 0, 0.05, 0.1, 0.2, 0.3, and 0.5） were investigated. The ...equal molar CoCrFeNi alloy with FCC structure exhibits high ductility but weak strength. With the addition of C element, both the hardness and strength of the CoCrFeNiCx high entropy alloys increase as well as the wear resistance. The solution strengthening and the lbrmation of hard carbide phase are the main thctor for the improved strength, hardness and wear resistance of CoCrFeNiC~ high entropy alloys.
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