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High entropy alloys exhibit a composition design route that different from conventional alloys. However, whether the high configurational entropy is the key factor that stabilizes the room temperature single phase solid solution is still under debate. Here we use a perturbation model to evaluate their phase stabilities. According to the calculation results of 7085 alloys, it clearly indicates that a stable single phase is rare when constituent elements increase. The effect of increased entropy cannot balance the fast-increased driving force for the formation of intermetallics. Although it is not favored by thermodynamics, the frequently observed room temperature single-phase solid solutions can still form due to dynamic effect, which from the other side, provides a method to tune the microstructure and therefore the mechanical properties.

Physical review / B 105(22), 224201 (2022). doi:10.1103/PhysRevB.105.224201, Achieving effective tuning of glass structures between distinct states is intriguing for fundamental studies and applications, but has previously turned out to be challenging in practice. High-entropy metallic glasses (HEMGs), as an emerging type of metallic glasses (MGs) based on the high-entropy effect, are expected to have more disordered and frustrated chemical short-range structure compared with conventional MGs. Therefore, HEMGs may offer possibilities for structure and properties tuning in glasses. In this work, we employ pressure as a tuning parameter and monitor the atomic structural evolution of a senary HEMG, Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7, up to ∼40 GPa using in situ synchrotron x-ray diffraction. Analysis of its structure factor in reciprocal space and reduced pair distribution function in real space both reveal a pressure-induced structural crossover at ∼20 GPa with a dramatic change in short-range order (SRO), while no similar phenomenon is observed in a conventional MG, Cu36Zr64, as a control sample, suggesting the pressure-induced highly tunable SRO in HEMGs originates from the local chemical complexity, namely, the high-entropy effect. These results confirm that enhanced flexibility and tunability of atomic structures could be achieved by introducing the high-entropy effect into MGs. Therefore, configurational entropy could be another dimension for exploring MGs with highly tunable structures and properties for various potential applications., Published by Inst., Woodbury, NY

In this paper, we report that two newly designed high entropy bulk metallic glasses (HE-BMGs), Ti20Hf20Cu20Ni20Be20 with a critical diameter of 2 mm, and Ti16.7Zr16.7Nb16.7Cu16.7Ni16.7Be16.7 with a critical diameter of 1.5 mm, can be fabricated by copper mold casting method. These newly developed HE-BMGs exhibited a high fracture strength over 2300 MPa. The glass forming ability and atomic size distribution characteristics of the HE-BMGs are discussed in detail. Moreover, a parameter δ′ was proposed to evaluate the atomic size distribution characteristics in different HEAs. It showed that this new parameter is closely related to the degree of lattice distortion and phase selection of high-entropy alloys. Adjusting the value of δ′ parameter by similar element substitution/addition would be beneficial for designing high entropy bulk metallic glasses.

Laser melting deposition with WC addition has been developed to fabricate high-strength CrMnFeCoNi-based high-entropy alloys-based composites. By this technique, a microstructure of compact refined equiaxed grains can be achieved, and the tensile strength can be remarkably improved. The sample with 5 wt% WC addition shows a promising mechanical performance with a tensile strength of 800 MPa and an elongation of 37%. The improvement in mechanical property may be attributed to the formation of Cr23C6 reinforcement precipitates, which could promote the heterogeneous nucleation of grains and hinder the propagation of slip bands.

In this paper, a laser metal deposition (LMD) process has been applied to the fabrications of CrMnFeCoNi high entropy alloys. The microstructures and mechanical properties of the CrMnFeCoNi alloys prepared using casting technique and LMD technique have been investigated. It has been found that the CrMnFeCoNi samples prepared using casting show a coarse dendritic structure. The microstructures of LMD samples contain both columnar grains and/or equiaxed grains, and the proportion of columnar grains and equiaxed grains can be adjusted by changing the laser power. Besides, the mechanical properties of LMD samples can be adjusted by changing laser power, due to columnar to equiaxed transitions (CET) that are effected by solidification mode and the heat flux direction of LMD process. It is worth to mention that the mechanical properties of the 1400 W samples produced using LMD are better than those produced by casting, which is rarely observed. Furthermore, CrMnFeCoNi alloys prepared using LMD show excellent mechanical properties at cryogenic temperatures.

In this paper, a laser melting deposition (LMD) technique has been applied to fabricate CrMnFeCoNi high entropy alloys (HEAs). The microstructures and tensile properties of CrMnFeCoNi HEAs prepared under different laser power and scanning strategies have been investigated. It has been observed that the laser power and scanning strategy have significant effects on the columnar to equiaxed transitions (CET) of the microstructure of LMD CrMnFeCoNi HEAs because of their effects on heat flux direction and the temperature gradient. Due to small molten size and rapid cooling rate in LMD process which results in a significant solute-trapping effect and thus avoids component segregation, the elements distribution of LMD samples are more homogeneous than as-cast samples. Besides, tensile properties of the LMD samples can be adjusted by changing laser power and scanning strategy, which be corresponding to the changes of microstructure.

The negative effects of thermal cycles in the process of additive manufacture present a challenge for the control of microstructure so as to fabricate the products with improved properties compared to cast. In this work, AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA) was prepared by laser metal deposition (LMD). Comparison with the cast samples, the LMD-fabricated EHEA showed significantly enhanced tensile strength (by 19.7%) and increased tensile ductility (by 56.4%). Such enhancement in mechanical properties owing to the refinement of the uniformly distributed eutectic-structure, which was composed of a ductile FCC(L12) phase and a strong BCC(B2) phase embedded with a high density of nano-precipitates. These nano-precipitates effectively pinned the dislocations, resulting strain hardening/dislocation accumulation capability. The present work provides a new strategy to utilize both the high cooling rates of LMD and the eutectic-structure characteristics for achieving homogeneous structures and superior mechanical properties to those prepared by traditional processing techniques.

A laser metal deposition (LMD) process has been applied to the fabrications of the (CrMnFeCoNi)1-xFex (x = 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) Multi-principal elements alloys (MPEAs). It is found that the LMD-fabricated (CrMnFeCoNi)50Fe50 alloy keeps a single-phase solid solution microstructure. Compared with the CrMnFeCoNi MPEA, the (CrMnFeCoNi)50Fe50 alloy obtains remarkably improved plasticity from 45% to 77%, while maintaining tensile strength (415 MPa to 470 MPa), due to the strain-induced FCC to BCC phase transformation. Furthermore, the (CrMnFeCoNi)50Fe50 alloy shows excellent mechanical properties at cryogenic temperatures. This alloy has lower cost and better mechanical property than the well-known CrMnFeCoNi MPEA by the addition of inexpensive Fe elements. The present work provides important pathways in the development of low-cost LMD-fabricated MPEA for cryogenic engineering applications.

In this work, a new multi-component (CrFeMoNbZr)Ox system was developed. The thin films presented dual-phase amorphous structures, comprising a dominant amorphous alloy phase and a small amount of an amorphous oxide phase. The thin films showed higher hardness and better corrosion resistance than a commercial Zr-based alloy. The combined properties of high hardness and superior corrosion-resistance make the amorphous thin film a candidate for coating materials on commercial Zr-based alloys for engineering applications.

The negative effects of thermal cycles in the process of additive manufacture present a challenge for the control of microstructure so as to fabricate the products with improved properties compared with conventional casting technique. In this work, AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) was prepared by laser metal deposition (LMD). Compared with conventionally cast EHEA samples, the LMD-fabricated EHEA samples showed significantly enhanced tensile strength (by 19.7%) and increased tensile ductility (by 56.4%). Such enhancement in tensile properties was attributed to the refinement of the uniformly distributed eutectic-structure, which improved the strain hardening/dislocation accumulation capability of the EHEA. The present work provides a new strategy to utilize both the high cooling rates of LMD and the eutectic-structure characteristics for forming refined homogeneous structures and thus achieving superior mechanical properties to those prepared by traditional processing techniques.

Refractory high-entropy alloys (RHEAs) are newly developed candidate materials for high-temperature applications. Among the existing RHEAs, NbMoTaW RHEA possesses the best mechanical properties with combined high strength, excellent thermal stability and softening resistance at elevated temperatures. However, the NbMoTaW RHEA is quite brittle at room temperature, which would restrict its application as structural material. Here, TixNbMoTaW RHEAs were developed by alloying Ti in the NbMoTaW RHEA. It shows that the room temperature ductility of the RHEAs increases from 1.9% of the NbMoTaW RHEA to 11.5% of the TiNbMoTaW RHEA, and the yield strength increases from 996 MPa of the NbMoTaW RHEA to 1455 MPa of the TiNbMoTaW RHEA. In addition, the TixNbMoTaW RHEAs keep stable single BCC structure up to their melt points. The present result indicates that Ti addition could effectively enhance both the ductility and strength of the NbMoTaW RHEA. The combined performance of superior mechanical properties and high thermal stability of the TixNbMoTaW RHEAs promises them an important role in engineering applications.

Graphene has shown many attractive properties while the difficulties in the fabrication of high-quality graphene have been a significant bottleneck in its applications. Here we report the discovery of high-quality graphene obtained from the solidified equiatomic CrFeCoNiC high-entropy alloy. Graphite flakes can be peeled off from the surface of the as-cast CrFeCoNiC high-entropy alloy, and single or multilayer graphene can be further exfoliated. The mechanical properties of the graphene are investigated by an atomic force microscope, and the result confirms the discovery of high-quality graphene. The transmission electron microscopy and Raman spectroscopy are applied to further characterize the quality of the graphene and show that the graphene has high-quality with few defects, comparable to the graphene obtained from highly oriented pyrolytic graphite. The thermodynamic calculation is applied to investigate the solidification process of the high-entropy alloy and reveals the mechanism of the formation of graphite on the surface.

Insufficient chemical activity of zero-valent iron (ZVI) is the main problem that limits its performance in degrading dyeing wastewater. Currently, the methods of creating acidic reaction condition and reducing the particle size of ZVI are widely used to improve the degradation activity of ZVI. However, they have disadvantages such as high reactor requirements and oxides accumulation. Herein, peculiar porous structural composites constructed with porous ferroalloy supported iron powders were prepared depending on magnetic force, the effects of pH, material structure, and powder size on the degradation performance of iron in Orange II solutions were detailedly investigated. The porous structure endowed the composite materials with greatly enhanced degradation performance, especially in near-neutral and alkaline environments, enable a cheap, fast, and durable degradation. The results show that the compositing porous ferroalloy with iron powder can largely increase the kinetic rate constant by more than 15 times, which is much more advantageous than increasing the specific surface area of the powder or increasing the acidity. This work reveals the determinants that affect the degradation performance of ZVI, and presents an effective method for tuning the properties of magnetic materials using porous structural composites.

The AlCrFeNiMo0.5Tix (x = 0, 0.25, 0.4, 0.5) high entropy alloys were prepared by copper mold suction casting, and the structures and aqueous corrosion behavior of the alloys were investigated in the present study. It shows that all of these alloys possess BCC + B2 structures at various Ti contents, while Ti element is enriched in ordered B2 phase. With increasing Ti content, the passive film becomes more protective. The charge transfer resistance (Rct) value increases from 229 kΩ · cm2 for the AlCrFeNiMo0.5 alloy to 635 kΩ · cm2 for the AlCrFeNiMo0.5Ti0.5 alloy. Meanwhile, the pitting potential (Epit) increases from 90 mV for the AlCrFeNiMo0.5 alloy to 410 mV for the AlCrFeNiMo0.5Ti0.5 alloy. The present results indicate that the corrosion resistance of the AlCrFeNiMo0.5Tix high entropy alloys has been significantly enhanced by Ti additions.

Nanostructured materials with large surface areas are continuing to be at the forefront of catalytic applications. But the nanostructure synthesis methods are often lengthy, costly and difficult. Here we report the first successful fabrication of metallic-glass (MG) hierarchical nanostructures by combining thermoplastic forming and electrochemical reduction process. By the simple synthesis technique, the oxide-derived MG nanorod arrays (OD-MG NRAs) electrode with higher specific surface area exhibits an enhanced catalytic activity towards hydrogen evolution reaction than that of untreated flat MG. The OD-MG NRAs electrode demonstrates efficient electrochemical hydrogen generation in an acidic electrolyte (10 mA cm−2 at overpotential of 63 mV; Tafel slope of 42.6 mV dec−1) and possesses impressive self-stabilizing catalytic activity over a long-term operation. These features promise an attractive catalyst for large-scale hydrogen production.

Since the treatment of wastewater containing azo dye presents problems worldwide, it is important to seek effective materials and technology for the purification of wastewater containing azo dye. Fe-based metallic glasses have been identified as promising materials for the decomposition of dyeing wastewater due to their high chemical activity resulting from their amorphous structure. It is imperative to further improve their degradation performance, and especially their durability, for potential application in wastewater purification. Here, composite structures constructed of porous Ni and amorphous Fe78Si9B13 powder with markedly enhanced degradation performance in Orange II solution were obtained by utilizing a magnet. Due to the favorable effects of structural electrocatalysis and high dispersity of the distinctive porous architecture in addition to its self-cleaning properties, the solid-liquid interface exhibited strong, continuous electrical and mass transport, and a compelling improvement in degradation performance was achieved. Based on degradation tests and spectrum analysis, the kinetic rate was improved over 11-fold. Moreover, ultra-high durability over 100 cycles was revealed in cycling tests. The results indicate that wastewater degradation performance can be greatly enhanced by properly combining Fe-based metallic glasses with porous material.

In this work, the essential mechanism of “loss of passivation” (LOP) effect for a 13 wt. % Cr-type martensitic stainless steel (MSS) is studied via electrochemical and microstructure approaches. The MSSs were quenched at 1030 °C and then tempered at 440−600 °C. Electrochemical results show that the tempering range for “LOP” is 460−540 °C. Severe corrosion occurred on 520 °C-tempered MSS after being immersed in Cl− containing solution for 35 min. Transmission electron microscopy (TEM) observation towards the corroded area of 1030-520 sample reveals the massive precipitation of nano-sized Cr-rich carbides, which is the essential cause for the “LOP” of MSSs.

Structural heterogeneity dominates energy-storage behavior of metallic glasses. Ti20Zr20Hf20Be20Cu7.5Ni12.5 high-entropy bulk metallic glass (HE-BMG) shows extraordinary energy-storage behavior under cryothermal cycling: the relaxation enthalpy monotonically increased with cryothermal cycling cycles, even after 240 cycles of treatment. By comparison, the relaxation enthalpy of Ti41Zr25Be22Ni12 BMGs reached a maximum only at 30 cycles and then dramatically decreased as prototypical BMGs reported. The as-cast HE-BMG demonstrates an extremely low fraction of loose-packing regions (~7.8%, fractions for Ti- and Zr-based BMGs are above 15.6%), indicating degraded structural heterogeneity that would induce smaller local internal stress during cryothermal cycling and eventually lead to the sluggish energy-storage behavior. In addition, the increase in the fraction of loose-packing regions accompanied by the energy storage also lead to significant improvement in ductility of the HE-BMG, the plastic strain increased from 0.6% (the as-cast sample) to 5.2% (the sample treated 240 cycles).

In this paper, a Laser Metal Deposition (LMD) technique has been applied to fabricate CoCrFeNiMo0.2 high-entropy alloys (HEAs). The microstructure, corrosion behavior and mechanical properties of LMD CoCrFeNiMo0.2 HEAs prepared under different laser power have been investigated. It was observed that the laser power had significant effects on the columnar crystal morphology in LMD CoCrFeNiMo0.2 HEAs. When increasing the laser power, the temperature gradient would decrease, leading to larger crystal size of columnar grains. The tensile properties at 293 K of the LMD CoCrFeNiMo0.2 HEAs could be adjusted by changing the laser power, which was corresponded to the changes of microstructure. With a decrease in temperature from 293 K to 77 K, the tensile strength and tensile ductility of the LMD 1400 W CoCrFeNiMo0.2 HEAs remarkably improved by ~70% and ~28%, to 928 MPa and 60%, respectively. In both 3.5 wt% NaCl solution and 1 mol/L H2SO4 solution, the CoCrFeNiMo0.2 exhibited higher corrosion resistance than 304 stainless steel substrate, CoCrFeNi and even lower corrosion current density than 316L stainless steel.