Composition Design Strategy for High Entropy Amorphous Alloys.

High entropy amorphous alloys (HEAAs) are materials that have received much attention in recent years. They exhibit many unique properties; however, research on their composition design method has not been deep enough. In this paper, we summarized some effective composition design strategies for HEAAs. By adjusting the atomic ratio from quinary bulk metallic glasses, Ti20Zr20Cu20Ni20Be20 HEAA with a high fracture strength of 2315 MPa was designed. By similar element addition/substitution, a series of Ti-(Zr, Hf, Nb)-Cu-Ni-Be HEAAs was developed. They possess good glass-forming ability with a maximum critical diameter of 30 mm. Combining elements from those ternary/quaternary bulk metallic glasses has also proved to be an effective method for designing new HEAAs. The effect of high entropy on the property of the alloy, possible composition design methods, and potential applications were also discussed. This paper may provide helpful inspiration for future development of HEAAs.

Influence of Annealing Process on Soft Magnetic Properties of Fe-B-C-Si-P Amorphous Alloys.

It is well known that the annealing process plays a key role in tuning the properties of Fe-based amorphous soft magnetic alloys. However, the optimal annealing process for a particular amorphous alloy is often difficult to determine. Here, Fe81.4B13.2C2.8Si1.8P0.8 and Fe82.2B12.4C2.8Si1.8P0.8 amorphous alloys (denoted as Fe81.4 and Fe82.2) were prepared to systematically study the effects of the annealing temperature and time on the soft magnetic properties. The results show that the optimum annealing temperature ranges of the Fe81.4 and Fe82.2 amorphous alloys were 623 K to 653 K and 593 K to 623 K, and their coercivity (Hc) values were only 2.0-2.5 A/m and 1.3-2.7 A/m, respectively. Furthermore, a characteristic temperature Tai was obtained to guide the choosing of the annealing temperature at which the dBs/dT begins to decrease rapidly. Based on the theory of spontaneous magnetization, the relationship between Tai and the optimum annealing temperature ranges was analyzed. When the annealing temperature was higher than Tai, the effect of the internal magnetic field generated by spontaneous magnetization on the relaxation behavior was significantly reduced, and the alloys exhibited excellent soft magnetic properties. It is worth indicating that when annealed at 603 K (slightly higher than Tai), the Fe82.2 amorphous alloys exhibited excellent and stable soft magnetic properties even if annealed for a long time. The Hc of Fe82.2B12.4C2.8Si1.8P0.8 amorphous alloys was only 1.9 A/m when annealed at 603 K for 330 min. This value of Tai is expected to provide a suggestion for the proper annealing temperature of other amorphous soft magnetic alloys.

Designing High Entropy Bulk Metallic Glass (HE-BMG) by Similar Element Substitution/Addition.

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.

Effect of cryogenic cycling on mechanical properties of ZrTiCuNiBe bulk metallic glass.

The effect of deep cryogenic cycle treatment (DCT) on Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit-1) bulk metallic glass (BMG) prepared from high-purity raw materials was investigated. After DCT, no obvious rejuvenation of the samples was detected. With an increasing number of cryogenic cycles, the hardness of the samples first decreased and then increased, the room-temperature compression plasticity first increased and then generally remained unchanged, and the impact toughness underwent almost no obvious change. The absence of rejuvenation was attributed to the high fragility index (47-50) and high glass forming ability (GFA) of the material. As lower purity of the raw materials is expected in practical applications, DCT of Vit-1 BMG prepared from low-purity raw materials was also performed. After DCT, the samples prepared with the lower-purity raw materials were clearly rejuvenated, and the room-temperature mechanical properties improved significantly.Both the compression plasticity and impact toughness reached peak values after 5 cryogenic cycles. The initial impurities (including Y and O) had a complex and comprehensive effect on the deformation mechanism of the BMG during DCT. Our findings indicate that the structural heterogeneity, fragility index, and GFA of the BMG alter the effect of DCT.

High-entropy induced a glass-to-glass transition in a metallic glass.

Glass-to-glass transitions are useful for us to understand the glass nature, but it remains difficult to tune the metallic glass into significantly different glass states. Here, we have demonstrated that the high-entropy can enhance the degree of disorder in an equiatomic high-entropy metallic glass NbNiZrTiCo and elevate it to a high-energy glass state. An unusual glass-to-glass phase transition is discovered during heating with an enormous heat release even larger than that of the following crystallization at higher temperatures. Dramatic atomic rearrangement with a short- and medium-range ordering is revealed by in-situ synchrotron X-ray diffraction analyses. This glass-to-glass transition leads to a significant improvement in the modulus, hardness, and thermal stability, all of which could promote their applications. Based on the proposed high-entropy effect, two high-entropy metallic glasses are developed and they show similar glass-to-glass transitions. These findings uncover a high-entropy effect in metallic glasses and create a pathway for tuning the glass states and properties.

Characterization of the microstructure and hardness of case-carburized gear steel.

The microstructure and hardness of case-hardened steel were investigated after carburizing and austenitizing at 820-900 °C, and oil quenching and tempering at 180 °C. The carburized case had a multiphase microstructure consisting of martensite, carbides, and retained austenite, and the maximum content of the retained austenite was 30%; the particle size range was 2-3 µm. The nano-hardness decreased from about 12 GPa near the surface to about 7 GPa in the core, and the microhardness decreased from 800 HV0.2 to 450 HV0.2. The in-depth distribution of the microhardness and nano-hardness showed a similar trend, and the ratio of nano-hardness to microhardness was about 15. The results were attributed to the fine particle size of the retained austenite and its even distribution in the martensite matrix and it could not lower the nano-hardness. The nano-hardness was relatively low in areas of the retained austenite (about 5.5 GPa), and pop-in effects were observed, indicating the phase transformation of the retained austenite during nanoindentation loading.

Influence of inorganic ions on degradation capability of Fe-based metallic glass towards dyeing wastewater remediation.

Metallic glasses (MGs) are promising candidates for catalysts with high efficiency for dyeing wastewater remediation, due to their metastable nature, disordered structure, and large residual stresses. However, dyeing wastewater usually contains a high concentration of inorganic ions which may have adverse effects on the degradation process, while the impacts of these ions on MGs' degradation capability have often been overlooked and still remain unknown. Thus, the roles of inorganic ions (Cl-, NO3-, SO42-, and H2PO4-) on the degradation of azo dye by Fe-based MG with nominal composition of Fe81Si4B14Cu1 were systematically investigated. The results showed that the inorganic ions have significant influence on MG's surface morphology, degradation capability, mineralization and durability. All these aspects need to be considered prior to application of MGs for azo dyes degradation in real natural contaminated water or saline wastewater.

Porous composite architecture bestows Fe-based glassy alloy with high and ultra-durable degradation activity in decomposing azo dye.

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.

Preparation of nanoparticles with an environment-friendly approach.

Developing various approaches for preparing high performance materials has long been topics and tasks both for scientists and for engineers. Despite that many methods have been developed for preparing nanomaterials, developing simple and environment-friendly ways for preparing nanomaterials is very attractive. Here a simple approach of synthesizing Fe3O4 nanoparticles by arc-discharge submerging in water was reported. The results showed that by this method Fe3O4 nanoparticles can be synthesized at large scale. The as-prepared Fe3O4 nanoparticles exhibited uniform spherical shape and their diameters varied with arc-discharging parameters. The experimental results showed that the size of the synthesized Fe3O4 nanoparticles can be controlled through adjusting the processing parameters. Since no vacuum system has been used, the synthesizing process is greatly simplified. In addition, only cheap deionized water and industrial iron bar are used and no pollution or harmful byproducts are found in the synthesis process. It indicated that the present approach is a simple, low-cost and environment-friendly one for preparing nanoparticles.

High-Performance Carbon Dioxide Electrocatalytic Reduction by Easily Fabricated Large-Scale Silver Nanowire Arrays.

An efficient and selective catalyst is in urgent need for carbon dioxide electroreduction and silver is one of the promising candidates with affordable costs. Here we fabricated large-scale vertically standing Ag nanowire arrays with high crystallinity and electrical conductivity as carbon dioxide electroreduction catalysts by a simple nanomolding method that was usually considered not feasible for metallic crystalline materials. A great enhancement of current densities and selectivity for CO at moderate potentials was achieved. The current density for CO ( jco) of Ag nanowire array with 200 nm in diameter was more than 2500 times larger than that of Ag foil at an overpotential of 0.49 V with an efficiency over 90%. The origin of enhanced performances are attributed to greatly increased electrochemically active surface area (ECSA) and higher intrinsic activity compared to those of polycrystalline Ag foil. More low-coordinated sites on the nanowires which can stabilize the CO2 intermediate better are responsible for the high intrinsic activity. In addition, the impact of surface morphology that induces limited mass transportation on reaction selectivity and efficiency of nanowire arrays with different diameters was also discussed.

One-pot preparation of nanoporous Ag-Cu@Ag core-shell alloy with enhanced oxidative stability and robust antibacterial activity.

Metallic core-shell nanostructures have inspired prominent research interests due to their better performances in catalytic, optical, electric, and magnetic applications as well as the less cost of noble metal than monometallic nanostructures, but limited by the complicated and expensive synthesis approaches. Development of one-pot and inexpensive method for metallic core-shell nanostructures' synthesis is therefore of great significance. A novel Cu network supported nanoporous Ag-Cu alloy with an Ag shell and an Ag-Cu core was successfully synthesized by one-pot chemical dealloying of Zr-Cu-Ag-Al-O amorphous/crystalline composite, which provides a new way to prepare metallic core-shell nanostructures by a simple method. The prepared nanoporous Ag-Cu@Ag core-shell alloy demonstrates excellent air-stability at room temperature and enhanced oxidative stability even compared with other reported Cu@Ag core-shell micro-particles. In addition, the nanoporous Ag-Cu@Ag core-shell alloy also possesses robust antibacterial activity against E. Coli DH5α. The simple and low-cost synthesis method as well as the excellent oxidative stability promises the nanoporous Ag-Cu@Ag core-shell alloy potentially wide applications.

A room-temperature magnetic semiconductor from a ferromagnetic metallic glass.

Emerging for future spintronic/electronic applications, magnetic semiconductors have stimulated intense interest due to their promises for new functionalities and device concepts. So far, the so-called diluted magnetic semiconductors attract many attentions, yet it remains challenging to increase their Curie temperatures above room temperature, particularly those based on III-V semiconductors. In contrast to the concept of doping magnetic elements into conventional semiconductors to make diluted magnetic semiconductors, here we propose to oxidize originally ferromagnetic metals/alloys to form new species of magnetic semiconductors. We introduce oxygen into a ferromagnetic metallic glass to form a Co28.6Fe12.4Ta4.3B8.7O46 magnetic semiconductor with a Curie temperature above 600 K. The demonstration of p-n heterojunctions and electric field control of the room-temperature ferromagnetism in this material reflects its p-type semiconducting character, with a mobility of 0.1 cm2 V-1 s-1. Our findings may pave a new way to realize high Curie temperature magnetic semiconductors with unusual multifunctionalities.

A nanoglass alloying immiscible Fe and Cu at the nanoscale.

Synthesized from ultrafine particles with a bottom-up approach, nanoglasses are of particular importance in pursuing unique properties. Here, we design a metallic nanoglass alloy from two components of ∼Cu64Sc36 and ∼Fe90Sc10 nanoglasses. With nanoalloying mutually immiscible Fe and Cu, the properties of the nanoglass alloys can be tuned by varying the proportions of the ∼Fe90Sc10 component. This offers opportunity to create novel metallic glass nanocomposites and sheds light on building a structure-property correlation for the nanoglass alloys.

Direct in situ observation of metallic glass deformation by real-time nano-scale indentation.

A common understanding of plastic deformation of metallic glasses (MGs) at room temperature is that such deformation occurs via the formation of runaway shear bands that usually lead to catastrophic failure of MGs. Here we demonstrate that inhomogeneous plastic flow at nanoscale can evolve in a well-controlled manner without further developing of shear bands. It is suggested that the sample undergoes an elasto-plastic transition in terms of quasi steady-state localized shearing. During this transition, embryonic shear localization (ESL) propagates with a very slow velocity of order of ~1 nm/s without the formation of a hot matured shear band. This finding further advances our understanding of the microscopic deformation process associated with the elasto-plastic transition and may shed light on the theoretical development of shear deformation in MGs.

Highly uniform and reproducible surface enhanced Raman scattering on air-stable metallic glassy nanowire array.

Preparation of surface enhanced Raman scattering (SERS) nanostructures with both high sensitivity as well as high reproducibility has always been difficult and costly for routine SERS detection. Here we demonstrate air-stable metallic glassy nanowire arrays (MGNWAs), which were prepared by a cheap and rapid die nanoimprinting technique, could exhibit high SERS enhancement factor (EF) as well as excellent reproducibility. It shows that Pd(40.5)Ni(40.5)P(19) MGNWA with nanowires of 55 nm in diameter and 100 nm in pitch possesses high SERS activity with an EF of 1.1 × 10(5), which is 1-3 orders of magnitudes higher than that of the reported crystal Ni-based nanostructures, and an excellent reproducibility with a relative standard deviation of 9.60% measured by 121 points over an area of 100 µm*100 µm. This method offers an easy, rapid, and low-cost way to prepare highly sensitive and reproducible SERS substrates and makes the SERS more practicable.