Nanostructured Alloys Research Articles

Magnetic and Structural Properties of Fe-Ni and Fe-Ni-Gr Based Nanostructured Alloys Synthesized by Mechanical Alloying

Nanostructured FeNi and FeNiGr alloys were successfully synthesized by the mechanical alloying technique. The alloys formation and different magnetic properties were studied as a function of milling time in the range of 0 to 30h by X-ray diffraction (XRD) technique, Scanning Electron Microscope (SEM) analysis and a Vibrating Sample Magnetometer (VSM) process. The X-ray diffraction study confirmed the apparition of the α-FeNi alloy after 5h of milling with an average crystallite size of 26.80nm. The crystallite size obtained after 30h of milling is 10.13nm, While, the lattice deformation increases from 0.431 to 0.935%. in addition, the analysis of the magnetization curves of the Fe-Ni alloys revealed original magnetic properties: super paramagnetic behavior, and especially saturation magnetization and significant coercivity. ​​​​​​​ Furthermore, the addition of graphene into FeNi alloy, reduced its crystallite size from 11.56 to 6.65 nm, and increases the lattice strain and lattice parameter from 0.631 to 0.748% and from 0.28686 to 0.28704nm, respectively. Which, enhanced these magnetic properties, by increasing its coercivity (Hc) from 16. 07 to 135.42 Oe and Mr from 1.73 to 5.87 emu/g, while the magnetization saturation is decreased from 153.25 to 123.06 emu/g.

Reforming nanostructured CuAg alloy to improve ductility and electrical conductivity

Nanostructured metallic materials often lack sufficient work-hardening capability and suffer premature necking during tensile loading. In this study, intense rolling strain was applied to process nanocrystalline CuAg sheet, and aging treatment was designed to further tailor the microstructure and properties. Features of grains, Ag precipitates and short-range ordered (SRO) structure were characterized by transmission electron microscope (TEM). Superior tensile strength of 600 MPa, uniform elongation of 10% and electrical conductivity of 86.7% IACS were successfully achieved. Mechanisms for the balanced mechanical and electrical properties were analyzed.

Rapid synthesis of trimetallic alloy PtPdNi nanosponges: structural, morphology and catalytic performance

Pt alloy nanostructures have been explored as promising anode catalysts for methanol oxidation reaction. However, the Pt catalyst have continued to face challenges that are yet to be resolved. Studies have shown that the size and geometric structure can influence a material’s catalytic activity and is related to the synthesis technique. In this study, PtPdNi nanostructures were produced at different synthesis duration. FESEM results show that all the samples exhibited nanosponges structure. The PtPdNi synthesized for 150 s, exhibited higher catalytically active toward methanol oxidation and resistance to carbon monoxide poisoning.

Micro- and nanostructure of additively manufactured, in-situ alloyed, magnetic spinodal Fe54Cr31Co15

Exploring the chemical micro- and nanostructure of metal alloys is essential to understand their physical properties, such as magnetism or hardness. Additively manufactured (AM) materials, e.g. via laser powder bed fusion (LPBF) followed by various heat treatments, can raise further questions concerning the printed material. For the in-situ alloyed, spinodal Fe54Cr31Co15 system, the macroscopic magnetic behaviour is greatly influenced by subsequent homogenisation and heat treatment steps. Here we show that the decomposition takes place on the nanometre scale, resulting in ferromagnetic FeCo-rich particles embedded in a Cr-rich matrix. By studying phenomena like chemical homogeneity, grain structure, and texture of the in-situ alloyed material at different scales, we reveal correlations between the heat treatment and the resulting nanostructure and its ferromagnetic properties. We found that the isothermal heating conditions determine the degree of phase segregation and that a homogenization step can be omitted for additively manufactured, in-situ alloyed FeCrCo alloys. The approach thereby offers insight and a path for also tailoring specific manufacturing parameters to provide the right quality printed materials with desired functionalities. For example, magnetic FeCrCo alloys are often used in electric motors or magnetic sensors, and the flexibility of the presented approach can lead to optimal use of the material.

COMBINED HYDRODYNAMIC INSTABILITIES AND THEIR ROLE IN THE FORMATION OF MICRO- AND NANOSTRUCTURES OF MATERIALS UNDER PLASMA INFLUENCES

The formation of micro- and nanostructures in titanium alloys subjected to combined treatment, including exposure to heterogeneous plasma flows and subsequent modification of the surface layer by a low-energy high-current electron beam, was studied. It is established that the main mechanism for the formation of structural-phase states of the micro and nanoscale range under the influence of plasma flows created by an electric explosion of conductors is the joint manifestation of Kelvin-Helmholtz and Rayleigh-Taylor instabilities at the interface of the media. It is shown that the maximum growth rate of disturbances with acceleration of the second layer g = 5 ×109 m/s2 and a transverse velocity of 0 m/s falls on the wavelength λm = 6.76 µm. If the velocity value of the second layer is u0 = 10 m/s, then λm = 6.23 µm, and at u0 = 50 m/s ‒ λm = 1.24 μm. The mechanism of formation of micro- and nanostructures during subsequent electron beam processing is a combined thermo-evaporative, concentration- capillary and thermoelectric instability. It is shown that if the influence of the concentration gradient, thermoelectric and evaporative effects is not taken into account, the maximum value of the growth rate will be observed at a wavelength of 113 µm. Taking into account thermoelectric phenomenon leads to a decrease in the value of λm to 48 μm. It is established that at the value of the thermoelectric coefficient γ = 0.1 V/K, the maximum growth rate is observed at λm = 300 nm.

Tungsten-based bcc-superalloys: Thermal stability and ageing behaviour

Tungsten is considered as a primary material for the divertor and first wall in many fusion reactor designs. There has been further interest in nano-structured multi-phase tungsten alloys and composites, such as oxide dispersion strengthened alloys, where interfaces may be harnessed as defect sinks to improve irradiation resilience, whilst also improving base mechanical strength, and potentially ductility. Here we further investigate the concept of tungsten-based ‘bcc-superalloys’ within the W-Ti-Fe ternary system, comprising W-TiFe, A2-B2, β-β’ nanostructures. Alloys were produced by arc melting and the microstructure controlled via thermal heat treatments, by solutionising at 1250 °C, followed by 750 °C ageing.The alloys were characterised using electron microscopy, including composition measurements, alongside hardness measurements. Building on our previous work, we have demonstrated that nano-scale B2 TiFe(W) forms within A2(W,Ti,Fe) in the W-Ti-Fe alloys, creating localised regions of the targeted A2-B2 (β-β’) precipitate reinforced structure. Further, here we evaluated ageing at 750 °C, where within the interdendritic domains decomposition consistent with B2TiFe(W) -> B2 + A2 and A2(Ti,Fe,W) -> A2 + A3 is proposed. An experimentally validated preliminary W-Ti-Fe ternary phase diagram has been produced, helping to understand the stable phases present and instructing onward optimisation of W-superalloys as a candidate material for fusion energy.

A Novel Hydro-Thermal Synthesis of Nano-Structured Molybdenum-Iron Intermetallic Alloys at Relatively Low Temperatures

Nano-structured Mo/Fe intermetallics were synthesized from precursors that contained 72/28% and 30/70% molar ratios of Mo/Fe, which were given as precursors A and B, respectively. These precursors were prepared from the co-precipitation of aqueous hot solutions of ammonium heptamolybdate tetrahydrate (AHM) and ferrous oxalate. The dry precipitates were thermally treated using TG-DSC to follow up their behavior during roasting, in an Ar atmosphere of up to 700 °C (10° K/min). The TG profile showed that 32.5% and 55.5% weight losses were measured from the thermal treatment of precursors A and B, respectively. The DSC heat flow profile showed the presence of endothermic peaks at 196.9 and 392.5-400 °C during the thermal decomposition of the AHM and ferrous oxalate, respectively. The exothermic peak that was detected at 427.5 °C was due to the production of nano-sized iron molybdate [Fe2(MoO4)3]. An XRD phase analysis indicated that iron molybdate was the only phase that was identified in precursor A, while iron molybdate and Fe2O3 were produced in precursor B. Compacts were made from the pressing of the nano-sized precursors, which were roasted at 500 °C for 3 h. The roasted compacts were isothermally reduced in H2 at 600-850 °C using microbalance, and the O2 weight loss that resulted from the reduction reactions was continuously recorded as a function of time. The influence of the reduction temperature and precursor composition on the reduction behavior of the precursors was studied and discussed. The partially and completely reduced compacts were examined with X-ray powder diffraction (XRD), a reflected light microscope (RLM), and a scanning electron microscope (SEM-EDS). Depending on the precursor composition, the reduction reactions of the [Fe2(MoO4)3] and Fe2O3 proceeded through the formation of intermediate lower oxides, prior to the production of the MO/Fe intermetallic alloys. Based on the intermediate phases that were identified and characterized at the early, intermediate, and final reduction degrees, chemical reaction equations were given to follow up the formation of the MoFe and MoFe3 intermetallic alloys. The mechanism of the reduction reactions was predicted from the apparent activation energy values (Ea) that were computed at the different reduction degrees. Moreover, mathematical formulations that were derived from the gas-solid reaction model were applied to confirm the reduction mechanisms, which were greatly dependent on the precursor composition and reduction temperature. However, it can be reported that nano-structured MoFe and MoFe3 intermetallic alloys can be successfully fabricated via a gas-solid reaction technique at lower temperatures.

Tuning thermoelectric figure of merit in Ag doped nanostructured PbSnTeSe alloy by entropy and band engineering phenomena

Advanced thermoelectric materials with novel chemistry and structure that exhibit superior functional properties are in high demand in today's scientific scenario. Engineered configurational entropy in bulk thermoelectric materials through complex chemical disorder is an emerging and potential approach to achieve exceptional thermoelectric properties over traditional material systems. In the current study, mechanical alloying (MA) and spark plasma sintering (SPS) were used to synthesize the high-density (>96%) nanocrystalline lead tin tellurium selenium (PbSnTeSe) high entropy alloy (HEA) with varied atomic concentrations of silver (Ag) doping (0–0.9 at%). The high entropy, band engineering and nanostructuring approach synergistically show a remarkable decrease to ultralow thermal conductivity (0.814 W/mK), resulting in a substantial increase in the power factor (14.16×10−4W/mK2). Thus, an excellent figure of merit (ZT=0.891) is achieved in PbSnTeSe doped with 0.9Ag HEA at 573 K, which is estimated as a 225% increase over the pristine PbSnTeSe HEA (ZT=0.396).

(Fe-Ni)-based glassy alloy containing Nb and Cu with excellent soft magnetic properties

Magnetic properties of amorphous Fe38Ni38B12P5Si3Nb3Cu1 alloy ribbons have been investigated in as-spun and annealed states with the aim of developing an ultrasoft magnetic material which is expected to be used in advanced information data devices. A small amount of simultaneous addition of Cu and Nb to a FeNi-metalloid amorphous alloy system caused the change in crystallization process from eutectic type to the primary one. After annealing at the temperature just below the glass transition temperature (Tg), the glassy alloy ribbon exhibit excellent soft magnetic properties, very low coercive force of 1 A/m and extremely high effective permeability of 7.5·104 at 1 kHz which have not been obtained for any kinds of Fe- and Ni-based amorphous alloys, in spite of relatively low saturation magnetic flux density of 0.86 T. The further increase in annealing temperature causes the precipitation of nanoscale fcc particles with a size of about 7 nm including a high density of planar faults and the resulting nanostructure alloy also exhibits good soft magnetic properties with low Hc below 2 A/m. The formation of nanostructure fcc-(Fe,Ni) + glass soft magnetic alloys is also novel. The syntheses of the new Fe-Ni-based glassy and nanocrystalline [fcc(Fe,Ni) + glass] alloy ribbons with ultrasoft magnetic properties are encouraging as a new type of energy saving-type soft magnetic material.

Computational and Experimental Design of the Octahedral PdFe Alloy Nanocatalyst for Hiyama Cross-Coupling and Environmental Pollutant Degradation

The research on various bimetallic nanoparticles (NPs) is rapidly expanding due to their widespread applications. However, the formation of bimetallic nanostructures in a facile way remains challenging. In the present study, an octahedral (Oh) PdFe alloy nanostructure was designed by following an aqueous medium synthesis strategy. Different metal precursor ratios were varied to observe the change in the shape and distribution of the Oh PdFe alloy nanostructure. Surprisingly, increasing the Fe content directed the finer growth of Oh morphology. However, increasing the Pd amount resulted in an uneven Oh PdFe alloy shape. The catalytic activity of the optimized Oh PdFe alloy was examined for Hiyama cross-coupling, and the degradation of dyes was scrutinized at different pH. The suggested alloy nanostructured catalyst exhibited improved catalytic behavior compared to other nanocatalysts, such as commercial catalyst Pd/C (95%), monometallic Pd Oh (98%), Fe NPs (15%), and PdFe NPs (85%), for the Hiyama cross-coupling reaction. The optimized alloy catalyst with less Pd and more Fe demonstrated 98% yield and excellent reusability up to the fifth consecutive cycle, conveying 80% yield. The stability of the Oh PdFe alloy nanocatalyst and the mechanistic aspects of Hiyama cross-coupling was supported by density functional theory. The degradation of both anionic dyes, Congo red, Eosin Y, and cationic rhodamine B, was performed under normal along with acidic and basic conditions. The degradation reaction was completed in an adequate time interval for all the dyes with no change in the morphology of the synthesized catalyst.

Interpretable design of Ir-free trimetallic electrocatalysts for ammonia oxidation with graph neural networks

The electrochemical ammonia oxidation to dinitrogen as a means for energy and environmental applications is a key technology toward the realization of a sustainable nitrogen cycle. The state-of-the-art metal catalysts including Pt and its bimetallics with Ir show promising activity, albeit suffering from high overpotentials for appreciable current densities and the soaring price of precious metals. Herein, the immense design space of ternary Pt alloy nanostructures is explored by graph neural networks trained on ab initio data for concurrently predicting site reactivity, surface stability, and catalyst synthesizability descriptors. Among a few Ir-free candidates that emerge from the active learning workflow, Pt3Ru-M (M: Fe, Co, or Ni) alloys were successfully synthesized and experimentally verified to be more active toward ammonia oxidation than Pt, Pt3Ir, and Pt3Ru. More importantly, feature attribution analyses using the machine-learned representation of site motifs provide fundamental insights into chemical bonding at metal surfaces and shed light on design strategies for high-performance catalytic systems beyond the d-band center metric of binding sites.

Inverted magnetic response in severe plastically deformed nanostructured high-entropy alloy

We present unconventional magnetization in a high-pressure torsion (HPT) CoCrFeNi nanostructured high-entropy alloy: (i) the temperature dependent magnetization protocol and DC susceptibility suggest effects of spin-clustering. Moreover, HPT-processing of the alloy produces a heterogeneous and metastable nanostructure, changing its supermagnetic character: turning superparamagnetic to superspin glass dynamics, (ii) the material shows an inverted magnetic hysteresis loop, an inversion of the central part of the loop where the remanent magnetization points in a direction opposite to the applied field. The exquisite tunability of this inverted magnetism as a function of field and temperature and its reproducibility in a quasi-equilibrium setting make this spin-clustering phenomenon unique. We account for this phenomenon in terms of a non-equilibrium population of oppositely polarized domains of an ordered ferromagnetic state, enabled through the nanostructured, highly distorted, and locally disordered crystalline medium.

Ultrafine Core@Shell Cu1Au1@Cu1Pd3 Nanodots Synergized with 3D Porous N-Doped Graphene Nanosheets as a High-Performance Multifunctional Electrocatalyst

Rationally combining designed supports and metal-based nanomaterials is effective to synergize their respective physicochemical and electrochemical properties for developing highly active and stable/durable electrocatalysts. Accordingly, in this work, sub-5 nm and monodispersed nanodots (NDs) with the special nanostructure of an ultrafine Cu1Au1 core and a 2-3-atomic-layer Cu1Pd3 shell are synthesized by a facile solvothermal method, which are further evenly and firmly anchored onto 3D porous N-doped graphene nanosheets (NGS) via a simple annealing (A) process. The as-obtained Cu1Au1@Cu1Pd3 NDs/NGS-A exhibits exceptional electrocatalytic activity and noble-metal utilization toward the alkaline oxygen reduction, methanol oxidation, and ethanol oxidation reactions, showing dozens-fold enhancements compared with commercial Pd/C and Pt/C. Besides, it also has excellent long-term electrochemical stability and electrocatalytic durability. Advanced and comprehensive experimental and theoretical analyses unveil the synthetic mechanism of the special core@shell nanostructure and further reveal the origins of the significantly enhanced electrocatalytic performance: (1) the prominent structural properties of NGS, (2) the ultrasmall and monodispersed size as well as the highly uniform morphology of the NDs-A, (3) the special Cu-Au-Pd alloy nanostructure with an ultrafine core and a subnanometer shell, and (4) the strong metal-support interaction. This work not only develops a facile method for fabricating the special metal-based ultrafine-core@ultrathin-shell nanostructure but also proposes an effective and practical design paradigm of comprehensively and rationally considering both supports and metal-based nanomaterials for realizing high-performance multifunctional electrocatalysts, which can be further expanded to other supports and metal-based nanomaterials for other energy-conversion or environmental (electro)catalytic applications.

A novel nano-spaced coherent FCC1/FCC2 eutectic high entropy alloy

A novel nanostructured Fe39Cr39Ni14C8 eutectic high entropy alloy (EHEA) was developed by rapid solidification. Detailed characterization reveals that the rapidly solidified Fe39Cr39Ni14C8 EHEA shows a nano-lamellar structure consisting of alternative FCC1 (∼120 nm in width) and FCC2 (∼80 nm) phases with a coherent relationship and possesses a high hardness of 463HV (∼4.5 GPa) and a high yield strength of 1.45GPa. They are mainly attributed to the unique ultrafine eutectic structure. This finding would shed new light on the development of FCC1/FCC2-nanostructured EHEAs with excellent mechanical properties.

Synthesis of noble/non-noble metal alloy nanostructures via an active-hydrogen-involved interfacial reduction strategy

Synthesis of noble/non-noble metal alloy nanostructures via an active-hydrogen-involved interfacial reduction strategy

Tuning the defects density in additively manufactured fcc aluminium alloy via modifying the cellular structure and post-processing deformation

In this study, using an L-PBF AlSi10Mg alloy with different microstructural properties, the typical structural defects caused by severe plastic deformation are investigated by scanning electron microscopy and high-resolution transmission electron microscopy. Microscopic characterization shows that the deformed L-PBF AlSi10Mg alloy exhibits a heterogeneous microstructure consisting of Al/Si interfaces and a high density of dislocations, stacking faults, and nanotwins. On the basis of experimental data, it is also shown that high stresses build up at the Al/Si interface due to incompatible deformation, enabling the activation of novel deformation modes that control the plastic deformation of the hard Si twin phase and amorphization in the solid state. The revealed synergy and novel deformation modes open a new horizon for the development of next-generation structural materials and provide insights into the atomically resolved structures of dislocations and GBs in nanostructured L-PBF alloys.

Synergistic effect of bimetallic Pd-Pt nanocrystals for highly efficient methanol oxidation electrocatalysts.

Metal nanocrystals (NCs) with controlled compositional and distributional structures have gained increasing attention due to their unique properties and broad applications, particularly in fuel cell systems. However, despite the significant importance of composition in metal NCs and their electrocatalytic behavior, comprehensive investigations into the relationship between atomic distribution and electrocatalytic activity remain scarce. In this study, we present the development of four types of nanocubes with similar sizes and controlled compositions (Pd-Pt alloy, Pd@Pt core-shell, Pd, and Pt) to investigate their influence on electrocatalytic performance for methanol oxidation reaction (MOR). The electrocatalytic activity and stability of these nanocubes exhibited variations based on their compositional structures, potentially affecting the interaction between the surface-active sites of the nanocrystals and reactive molecules. As a result, leveraging the synergistic effect of their alloy nanostructure, the Pd-Pt alloy nanocubes exhibited exceptional performance in MOR, surpassing the catalytic activity of other nanocubes, including Pd@Pt core-shell nanocubes, monometallic Pd and Pt nanocubes, as well as commercial Pd/C and Pt/C catalysts.

Tunable reactivity of silver nanoclusters: a facile route to synthesize a range of bimetallic nanostructures.

Quantized energy levels and unique optoelectronic properties of atomically precise noble metal nanoclusters (NCs) have made them important in materials science, catalysis, sensors, and biomedicine. Recent studies on the profound chemical interactions of such NCs within themselves and with ultrasmall plasmonic nanoparticles (NPs) indicate that depending on the size, shape, and composition of the second reactant, NCs can either take part in colloidal assembly without any chemical modifications or lead to products with atoms exchanged. Anisotropic NPs are a unique class of plasmonic nanomaterials as their sharp edges and protrusions show higher chemical reactivity compared to flat surfaces, often leading to site-specific growth of foreign metals and metal oxide shells. Here, using chemical interactions between gold nanotriangles (AuNTs) and Ag NCs of different compositions, we show for the first time that metal atom etching, alloying/atom exchange, and colloidal assembly can all happen at a particular length scale. Specifically, Ag25(DMBT)18 NCs (denoted as 1), upon reacting with AuNTs of ∼57 nm edge length, etch gold atoms from their sharp tips and edges. Simultaneously, the two nanosystems exchange metal atoms, resulting in Ag-doped AuNTs and AuxAg24-x(DMBT)18 (x = 1, 2). However, another Ag NC with the same metallic core, but a different ligand shell, namely, Ag25H22(DPPE)8 (denoted as 2), creates dendritic shells made of Ag, surrounding these AuNTs under the same reaction conditions. Furthermore, we show that in the case of a more reactive thiol-protected Ag NC, namely, Ag44(pMBA)30 (denoted as 3), gold etching is faster from the edges and tips, which drastically alters the identities of both the reactants. Interestingly, when the AuNTs are protected by pMBA, 3 systematically assembles on AuNTs through H-bonding, resulting in an AuNT core-Ag NC shell nanocomposite. Thus, while shedding light on various factors affecting the reactivity of Ag NCs towards AuNTs, the present study proposes a single strategy to obtain a number of bimetallic nanosystems of targeted morphology and functionality.

Fabricating FeCrCoZrLa High Entropy Alloy towards Enhanced Photocatalytic Degradation of Methylene Blue Dye

Fe20Cr20Co20Zr20La20 (at. %) high entropy alloy (HEA) using mechanical alloy (MA) was synthesized by an equiatomic ratio as a function of milling times (0h, 5h, 10h, 20h, 30h, and 50h). The HEA alloys were characterized with X-ray diffractometer (XRD), scanning electron microscopy (SEM), X-ray Energy-Dispersive Spectroscopy (EDX), transmission electron microscopy (TEM), and Differential thermal analysis (DTA). After 50 hours of grinding, the BCC crystalline phase was formed and the crystallite size and microstrain were calculated at 4.7 nm and 1.95 nm, respectively. TEM image of 50 hours of milled powders also confirms a nanocrystalline structure. Using solar energy, visible light photocatalysis is a promising method for removing environmental pollution. The photocatalytic effect of the synthesized nanostructured alloy on aqueous solutions containing methylene blue (MB) was investigated under xenon light. Photocatalytic degradation of the synthesized sample was evaluated by calculating the absorbance drops of the UV–Vis absorption spectra (methylene blue 664 nm).The degradation of the nanostructured alloy for MB was found as 89.76% after 120 min. This implies that the photocatalytic degradation rate is relatively high, and the obtained alloy has been used in practice for the degradation of methylene blue dye effectively.

Stabilizing nanograined Fe-Cr alloy by Si-assisted grain boundary segregation

• Si promotes GB segregation of Cr in the NG Fe-8Cr-1Si treated by SMGT and annealing. • Cr segregation increases with the decrease of grain size, which is related to high- density GND. • NG Fe-8Cr-1Si has enhanced thermal stability and hardness due to Cr segregation. • Additions attractive to solute can stabilize NG binary alloys with weak segregation tendency. Intentional solute segregation at grain boundary (GB) can effectively stabilize the nanograined alloys by reducing the excess energy and mobility of GB, but it usually works for binary alloys with sufficient GB segregation tendency. Here, we found that the segregation of Cr can be enhanced in a nanostructured Fe-8Cr alloy with insufficient GB segregation tendency through the interaction of another solute Si (1.0 wt.%). After surface mechanical grinding treatment and subsequent annealing, the nanograined Fe-8Cr-1Si is more thermally stable than the nanograined Fe-8Cr, which is mainly attributed to the Si-enhanced Cr segregation as observed by Super-X energy-dispersive X-ray spectroscopy (EDS) mapping system. With the grain refinement to nanoscale, the thermal stability is further improved due to the increase of Cr content at GBs and the precipitates formed at appropriate high temperatures. The present finding provides guidance for the development of advanced nanostructured ternary alloys.