Eutectic alloys with two alternating phases in the microstructure are well known for their excellent mechanical properties as well as superior castability. In this review, we have surveyed a large ...number of eutectic/near-eutectic alloys, their recent advancement mostly in Al-, Ni-, Ti-, Fe-base binary, ternary, multicomponent, and high entropy alloy systems. The fundamental of the growth mechanisms, interface instability, and different types of eutectic reactions are discussed. The effect of alloy addition on the evolution of nano-/ultrafine eutectic microstructure upon solidification, the morphology of phases, and their length scale in the range of 80 nm–2 μm, have been thoroughly illustrated with examples and case studies. The adopted methods to find eutectic composition in multicomponent systems have been guided. The enhanced hardness, and superior yield strength under tension and compression up to 2.5 GPa at room temperature as well as at high temperature up to 1000 °C has been correlated with the microstructure. The mechanism of slip transfer through the lamellae interface and the role of elastic constants of the individual phases on the evolved plasticity have been interlinked. Furthermore, an insight to the functional and critical mechanical properties, especially the evolution of soft magnetic properties, large fatigue limit, high temperature creep behavior, wear and corrosion resistance of a large number of eutectic alloys are discussed along with the engineering applications.
•Advancement in binary, ternary, multicomponent, high entropy eutectic/near-eutectic has been reviewed.•Effect of alloy addition on microstructure, morphology, and length-scale are illustrated with case studies.•Functional and critical mechanical properties for engineering applications are discussed.
This paper demonstrated a capric acid–palmitic acid–stearic acid ternary eutectic mixture/expanded graphite (CA–PA–SA/EG) composite phase change material (PCM) for low-temperature heat storage. The ...CA–PA–SA ternary eutectic mixture with a mass ratio of CA:PA:SA=79.3:14.7:6.0 was prepared firstly, and its mass ratio in the CA–PA–SA/EG composite can reach as high as 90%. The melting and freezing temperatures of CA–PA–SA/EG composite were 21.33°C and 19.01°C, and the corresponding latent heat were 131.7kJkg−1 and 127.2kJkg−1. The CA–PA–SA/EG composite powders can be formed into round blocks by dry pressing easily, with much higher thermal conductivity than CA–PA–SA. Thermal performance test showed that the increasing thermal conductivity of CA–PA–SA could obviously decrease the melting/cooling time. Thermal property characterizations after 500 heating/cooling cycles test indicated that CA–PA–SA/EG composite PCM had excellent thermal reliability. Based on all these results, CA–PA–SA/EG composite PCM is a promising material for low-temperature thermal energy storage applications.
In this work, a novel Ni1.5CrCoFe0.5Mo0.1Nb0.68 eutectic HEA coating with nano-lamellar microstructure was successfully designed by binary eutectic compositions strategy, thermodynamic calculation ...and simple experimental approach. Compared with the predicted eutectic compositions, the actual eutectic composition had a higher Nb content due to the increased solid solubility of Nb in the FCC phase. The Ni1.5CrCoFe0.5Mo0.1Nbx (x = 0.55 hypoeutectic, 0.68 eutectic, 0.8 hypereutectic) HEA coatings were prepared by laser cladding, which were composed of FCC phase with lattice parameter of a = ~3.59 Å and Laves phase with lattice parameter of a = b = ~4.82 Å and c = ~7.80 Å. The FCC phase was enriched in Ni, Cr, Co and Fe elements, while the Laves phase was enriched in Nb and Mo elements. Typical eutectic lamellar and hypoeutectic/hypereutectic microstructures were obtained at the central regions, while the columnar crystals formed at the interfacial regions. The average micro-hardness of Nb0.55, Nb0.68 and Nb0.8 coatings were calculated as ~573.5 HV, ~665.8 HV and ~715.6 HV respectively. From x = 0.55 to x = 0.8, the wear resistance of Ni1.5CrCoFe0.5Mo0.1Nbx HEA coatings are increased, and the dominant wear mechanism of the HEA coatings transforms from adhesive wear to abrasive wear.
Display omitted
•A feasible design strategy for laser-cladded eutectic HEA coatings was proposed.•A novel Ni1.5CrCoFe0.5Mo0.1Nb0.68 eutectic HEA coating with nano-lamellar microstructure was successfully prepared.•Typical eutectic microstructures were obtained at central regions, while columnar crystals formed at interfacial regions.•The Nb content of actual eutectic composition high than that of predicted composition.
As emerging eutectic mixtures, deep eutectic electrolytes (DEEs) show unique properties for Li‐metal batteries (LMBs). However, the limited choice and inferior electrode compatibility hinder their ...further development in LMBs. Herein, we report a new 1,2‐dimethylimidazole (DMIm)‐based deep eutectic gel polymer electrolyte induced by Li−N interaction. We demonstrate that incorporating electron‐withdrawing polyvinylidene difluoride (PVDF) polymer into the DMIm‐based DEE changes the coordination environment of Li+ ions, leading to a high transference number of Li+ ions (0.65) and superior interface stability between the electrolyte and Li anode. The deep eutectic gel polymer electrolyte exhibits excellent non‐flammability, high ionic conductivity (1.67 mS cm−1 at 30 °C), and high oxidation voltage (up to 4.35 V vs. Li/Li+). The Li||LFP cell based on the newly developed deep eutectic gel polymer electrolyte can achieve superior long‐term cycling stability at a wide range of rates.
A new Li−N interaction induced 1,2‐dimethylimidazole (DMIm)‐based deep eutectic gel polymer electrolyte is reported. The electron‐donating DMIm dissociates LiTFSI well to form a deep eutectic electrolyte (DEE). The incorporation of polyvinylidene difluoride (PVDF) further changes the coordination environment of the Li+ ions. This kind of gel polymer electrolyte exhibits high ionic conductivity and electrochemical stability and enables the excellent long‐term cycling performance for Li/LFP cells.
Display omitted
► Natural products were used as a source for deep eutectic solvents and ionic liquids. ► We define own chemical and physical properties of natural deep eutectic solvents. ► ...Interaction between natural deep eutectic solvents and solutes was confirmed by NMR. ► The developed natural deep eutectic solvents were applied as green media.
Developing new green solvents is one of the key subjects in Green Chemistry. Ionic liquids (ILs) and deep eutectic solvents, thus, have been paid great attention to replace current harsh organic solvents and have been applied to many chemical processing such as extraction and synthesis. However, current ionic liquids and deep eutectic solvents have still limitations to be applied to a real chemical industry due to toxicity against human and environment and high cost of ILs and solid state of most deep eutectic solvents at room temperature. Recently we discovered that many plant abundant primary metabolites changed their state from solid to liquid when they were mixed in proper ratio. This finding made us hypothesize that natural deep eutectic solvents (NADES) play a role as alternative media to water in living organisms and tested a wide range of natural products, which resulted in discovery of over 100 NADES from nature. In order to prove deep eutectic feature the interaction between the molecules was investigated by nuclear magnetic resonance spectroscopy. All the tested NADES show clear hydrogen bonding between components. As next step physical properties of NADES such as water activity, density, viscosity, polarity and thermal properties were measured as well as the effect of water on the physical properties. In the last stage the novel NADES were applied to the solubilization of wide range of biomolecules such as non-water soluble bioactive natural products, gluten, starch, and DNA. In most cases the solubility of the biomolecules evaluated in this study was greatly higher than water. Based on the results the novel NADES may be expected as potential green solvents at room temperature in diverse fields of chemistry.
In this study, CoCrFeNiTax (x value in molar ratio, x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.75) high entropy alloys were prepared to investigate the alloying effects of Ta on the microstructures and ...mechanical properties. With the addition of Ta element, the microstructure changed from an initial single FCC solid solution (x = 0) to a hypoeutectic microstructure (x = 0.1–0.3), then to a fully eutectic microstructure (x = 0.4) with a mixture of FCC and Co2Ta-type Laves phases, and finally to a hypereutectic microstructure (x = 0.5–0.75). The Ta-free (CoCrFeNi) alloy showed high ductility but low strength. With the addition of Ta, the yield strength and hardness of the CoCrFeNiTax alloys increased but decreased in ductility. Therein, the fully eutectic CoCrFeNiTa0.4 alloy displayed a high fracture strength of 2293 MPa with a compression plasticity of 22.6%. The regular/uniform ultrafine lamellae structure was the primary reason for the remarkable properties of the CoCrFeNiTa0.4 eutectic high entropy alloys.
Display omitted
•The fully eutectic CoCrFeNiTa0.4 alloy displayed excellent mechanical properties.•The ultrafine lamellar microstructure was obtained using the direct solidification method.•The ultrafine lamellar microstructure contributed high strength and hardness.
Instead of conventional CoCrFeNiHfx high-entropy alloys (HEAs), we investigated the evolution of microstructure and compressive mechanical properties of (CoCrFeNi)x(Co0.26Cr0.07Fe0.16Ni0.31Hf0.4) ...HEAs with varying x. Increasing x from 0.5 to 1.0, the microstructure changes from hyper-eutectic ones consisting of primary Laves phase and eutectic structure (x < 0.7), firstly to eutectic ones consisting of alternative FCC and Laves phase (x = 0.7 and 0.8), and finally to hypo-eutectic ones consisting of primary FCC phase and eutectic structure (x > 0.8). Interestingly, two different morphologies of eutectic microstructures are observed when x = 0.7 and 0.8 probably due to different fusion entropies of each phase. Increasing x from 0.5 to 1.0 reduces the yield strength from 1661 ± 64 to 688 ± 17 MPa but enhances the compressive ductility due to an increased fraction of soft FCC phase from ~0.39 to ~0.74. The second phase strengthening is the main strengthening mechanism. Importantly, when x = 0.9 and 1.0, these two alloys are not fractured when the strain reaches 0.5, one of which shows a large yield strength of 1028 ± 45 MPa (x = 0.9). Compared with conventional CoCrFeNiHfx, the studied HEAs exhibit a much better combination of compressive strength and ductility.
Display omitted
•(CoCrFeNi)x(Co0.26Cr0.07Fe0.16Ni0.31Hf0.4) microstructure changes from hyper-eutectic to hypo-eutectic with x increase.•Eutectic point is simultaneously obtained when x = 0.7 and x = 0.8 of (CoCrFeNi)x(Co0.26Cr0.07Fe0.16Ni0.31Hf0.4).•The eutectic microstructure changes from irregular lamella to regular lamella when increasing x value.•(CoCrFeNi)x(Co0.26Cr0.07Fe0.16Ni0.31Hf0.4) have a better combination of compressive strength and ductility than CoCrFeNiHfx.
Selective laser melting (SLM), a novel approach for one-step melting and solidifying ceramic powder beds layer by layer without post-process of degreasing and sintering, has been developed to ...directly prepare highly dense (>95 %) Al2O3/GdAlO3(GAP) eutectic composite ceramics with large smooth surfaces. Compact net-shaped plates with the maximum size of 73 × 24 × 5 mm3 are obtained by different strategies of laser pre-heating and multi-tracks’ deposition without any binders. Combined with the finite element thermodynamic coupling simulation results, it is proved that the stress between the substrate and depositions during SLM can be greatly reduced by the step-up preheating, and thus effectively improving the ceramic forming quality. The macro-morphology, microstructure evolution, rapid solidification behavior and mechanical properties of the SLM-ed eutectic ceramics are systematically investigated at different laser processing parameters. The microstructure transforms from ultra-fine irregular eutectic to complex regular eutectic with the increase of the scanning rate. The average eutectic spacing, and solidification rate has an approximately linear relationship consistent with the Jackson-Hunt (JH) model. The microhardness and fracture toughness can reach 17.1 ± 0.2 GPa and 4.5 ± 0.1 MPa·m1/2, respectively. The results indicate that SLM method is a highly effective technique for fabricating high-performance net-shaped structural composite ceramics.
Dual-phase microstructures arising out of eutectic reactions offer several advantages: ease of casting, composite properties and tunable characteristic length scale of the phases. Eutectic high ...entropy alloys (EHEA) with a multi-component solution phase and a hard intermetallic phase are candidate materials to identify alternate high-temperature materials. Alloying elements can be chosen to improve the resistance to lamellar microstructure degradation and coarsening. In this work, we present the CALPHAD guided design of a hypo-eutectic high entropy alloy CoCrFeNiTa0.395 with primary dendritic FCC phase and fine eutectic (FCC solution + Laves phase) microstructure possessing good high-temperature mechanical properties. The primary FCC phase fraction is 0.42 ± 0.02. The interlamellar spacing of the eutectic is 0.69 ± 0.12 μm. The alloy exhibited a balanced yield strength of 1303 ± 18 MPa, a fracture strength of 2237 ± 23 MPa and a fracture strain of 0.3 under room temperature compression testing. The mechanism for change in the lamellar morphology during deformation at temperatures beyond 0.8 TE is explained schematically. Strain field distribution obtained by FEM simulation correlates well with the observed microstructure gradients in the deformed samples. The formation of nano-scale precipitates in the low strain rate deformation is attributed to thermal effects. High-temperature precipitation of two types of precipitates (L12 ordered and Ni3Ta type) in the FCC-solution phase extended the useable temperature range of this alloy.
PDF
