Nanostructured Alloys Research Articles

Multi-skeletal PtPdNi nanodendrites as efficient electrocatalyst with high activity and durability towards oxygen reduction reaction

Engineering alloy nanostructures with a combination of highly active noble metals (Pt and Pd) and less electronegative non-noble metal (Ni) is found to be crucial for improving surface reactivity by enriching with active Pt sites. Herein, a multi-skeletal PtPdNi nanodendrites (NDs) was successfully formed by a simple one-pot method with structure directing agent. The modification of Pt electronic structure and their interaction due to compressive strain were explored using benchmark characterization techniques, which showed that the PtPdNi NDs possess Pt-enriched surface, corroborating to more active catalyst sites for oxygen reduction reaction (ORR) in acidic medium. The PtPdNi NDs have a higher electrochemical surface area (63 m2 g−1) and an earlier onset potential (1.01 V) than PtPd NDs, PtNi NDs, and commercial Pt/C catalysts, indicating the outstanding ORR performance. The high mass and specific activities, as well as superior durability after accelerated degradation test (ADT), highlight the remarkable electrocatalytic performance of PtPdNi NDs over others. As a result, enhancing Pt utilization through the formation of PtPdNi NDs could be a reliable strategy to improve ORR electrocatalysis for polymer electrolyte membrane fuel cell (PEMFC) applications.

On the microstructure and tensile behaviour of nanostructured NiTi alloy produced by electroplastic rolling

Electroplastic rolling was employed to produce nanostructured (NS), near-equiatomic NiTi alloy from a coarse grained NiTi nugget (ingot), which was produced using vacuum induction melting, followed by quenching in water from a temperature of 800°C. The microstructure of NS NiTi was characterized using X-ray Diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis revealed that the NS NiTi is predominantly martensitic at room temperature, with less than ≈10 % of the austenite phase. The NS NiTi alloy has an average grain size of ≈36 nm. TEM investigation confirmed the presence of grains that are less than 10 nm in size and no amorphous zones were detected. The NS martensitic NiTi alloy specimens were tested in tension at two different strain rates (10−2 and 10−1 s−1). In contrast to a stress-strain profile expected in a martensitic NiTi alloy, the stress-strain curves show conventional tensile behaviour. The observed UTS was high, around ≈1800 MPa, with a less than usual elongation to failure of ≈6 %. The presence of dimples on the fracture surfaces can be seen in scanning electron microscopy (SEM) images, which is indicative of ductile fracture. The role of grain size in the observed deformation and fracture features is also discussed.

Nanomechanical tribological characterisation of nanostructured titanium alloy surfaces using AFM: A friction vs velocity study

Medical-grade titanium alloys used for orthopaedic implants are at risk from infections and complications such as wear and tear. We have recently shown that hydrothermally etched (HTE) nanostructures (NS) formed on the Ti6AlV4 alloy surfaces impart enhanced anti-bacterial activity which results in inhibited formation of bacterial biofilm. Although these titanium alloy nanostructures may resist bacterial colonisation, their frictional properties are yet to be understood. Orthopaedic devices are encapsulated by bone and muscle tissue. Contact friction between orthopaedic implant surfaces and these host tissues may trigger inflammation, osteolysis and wear. To address these challenges, we performed simulation of the contact behaviour between a smooth control Ti6Al4V alloy and HTE surfaces against a hardwearing SiO2 sphere using Atomic Force Microscopy (AFM) in Lateral Force Microscopy mode. The friction study was evaluated in both air and liquid environments at high (5 Hz) and low (0.5 Hz) scan velocities. Lower scan velocities demonstrated opposing friction force changes between the two mediums, with friction stabilising at higher velocities. The friction measured on the NS alloy surfaces was reduced by ~20% in air and ~80% in phosphate buffered saline, in comparison to the smooth control surface, displaying a non-linear behaviour of the force applied by the AFM tip. Changes in friction values and cantilever scan velocities on different substrates are discussed with respect to the Stribeck curve. Reduced friction on nanostructured surfaces may improve wear resistance and aid osseointegration.

Nanostructured TiC dispersion-strengthened tungsten composite with remarkably improved He ion irradiation resistance

Improving the irradiation resistance of W alloys is vital to their application of plasma facing materials in future fusion reactors. In this work, quasi-spherical tungsten nanoparticles synthesized by thermal plasma were mixed with nanosized TiC to sinter nanostructured TiC dispersion-strengthened tungsten alloy. As-obtained W-TiC composite exhibited high relative density of 99.14% with suppressed grain size of about 1.12 μm, together with well-dispersed TiC with size 50–100 nm into W grains. More importantly, semi-coherent W/TiC interface with diffusion layer of about 25 nm was formed, which highlights the tight connection between W and TiC. Furthermore, He ions irradiation results indicated that W-TiC composite exhibited excellent irradiation resistance with a damage depth of about 9.53 μm, which is much lower than 18.26 μm of pure W. Mechanism investigation indicated that the remarkably improved He ion irradiation resistance was attributed to the efficient capture and annihilation of irradiation-induced defects by grain boundaries and phase interfaces.

Microstructural Characterization and Hardness Study of Nanostructured CoCrFeNi High Entropy Alloys with Dual Effect of Y and Nano-Sized Y2O3 Additions

Microstructural Characterization and Hardness Study of Nanostructured CoCrFeNi High Entropy Alloys with Dual Effect of Y and Nano-Sized Y2O3 Additions

Effect of Cr Addition on the Milling Process and Properties of Nanostructured Cu Alloys Prepared by Mechanical Alloying

Effect of Cr Addition on the Milling Process and Properties of Nanostructured Cu Alloys Prepared by Mechanical Alloying

Helium interaction with solutes and impurities in neutron-irradiated nanostructured ferritic alloys: A first principles study

Density functional theory (DFT) calculations are performed to explore the binding between He and alloying solutes, impurities, and transmutation products expected in neutron irradiated nanostructured ferritic alloys (NFAs), here 14YWT is taken as an example. Elements that exhibit significant binding (attraction) with an interstitial He are: Y (binding energy = 0.46 eV), Mg (0.32), O (0.33), Ti (0.16), and C (0.15). Those that provide significant binding to a substitutional He are: O (1.44), Y (1.24), N (0.73), H (0.56), Mg (0.52), Ti (0.34), Si (0.34), C (0.33), Al (0.32), Ni (0.26), Ta (0.23), and Mn (0.16). The presence of these elements in Fe matrix could reduce the transport of He towards oxide particles, dislocations, and internal boundaries, and could promote He bubble nucleation in the matrix. For convenience, we compile existing binding energy data of He with Hen and HenV (He-vacancy) clusters. Dissociation pathway analysis reveals that, in general, the most likely dissociation of a HenV cluster is by a sequential emission of individual He atoms. Furthermore, larger bubbles are more prone to dissociation than smaller ones. In addition, we estimate the binding energy (segregation energy) of He in bulk Y2Ti2O7 (YTO) single crystal, YTO/Fe interface, and YTO particle embedded in Fe, with respect to interstitial He in Fe, from existing formation energies of He in these structures. We also compile available data of He binding with Fe self-interstitial atom (SIA), SIA clusters, and edge and screw dislocations. Note that given the absence of DFT data, the binding with SIA clusters and dislocations are gathered from simulations with empirical potentials. The data presented in this paper is important to inform multiscale simulations of He bubble accumulation.

Comprehensive investigations on radiation shielding efficacy of bulk and nano Pb-Sn-Cd-Zn alloys

The alloys with composition: where were fabricated at nano-scale as well as bulk scale using the convention melt quench technique. Different characterization techniques such as Transmission Electron Microscopy (TEM), Field Emission-Scanning Electron Microscopy (FE-SEM) and Energy Dispersive Spectroscopy (EDS) analysis were performed to verify the particle size reduction to nano-scale, surface morphology and elemental composition of Pb60Sn20CdxZn(20-x) alloy systems. These nano-structured and bulk alloy systems were experimentally investigated and compared for their potential use in the radiation shielding applications. Further, radiation shielding effectiveness against electron beam, proton beam, alpha and heavy carbon ion beams has also been investigated for fabricated bulk alloys using Geant4 simulations. Present theoretical and experimental analysis affirmed that the radiation shielding efficacy gets enhanced for ball-milled PbSnCdZn nano alloy specimens as compared to bulk counterparts.

Manufacture-friendly nanostructured metals stabilized by dual-phase honeycomb shell

Refining grains to the nanoscale can greatly enhance the strength of metals. But the engineering applications of nanostructured metals are limited by their complex manufacturing technology and poor microstructural stability. Here we report a facile “Eutectoid element alloying→ Quenching→ Hot deformation” (EQD) strategy, which enables the mass production of a Ti6Al4V5Cu (wt.%) alloy with α-Ti grain size of 95 ± 32 nm. In addition, rapid co-precipitation of Ti2Cu and β phases forms a “dual-phase honeycomb shell” (DPHS) structure along the grain boundaries and effectively stabilizes the α-grains. The instability temperature of the nanostructured Ti6Al4V5Cu alloy reaches 973 K (0.55Tm). The room temperature tensile strength approaches 1.52 ± 0.03 GPa, which is 60% higher than the Ti6Al4V counterpart without sacrificing its ductility. Furthermore, the tensile elongation at 923 K exceeds 1000%. The aforementioned strategy paves a new pathway to develop manufacture-friendly nanostructured materials and it also has great potential for application in other alloy systems.

Optical investigations of Cu2CdSnS[formula omitted] quaternary alloy nanostructure for indoor optical wireless communications

The development of high-performance nano-luminophores based on luminescent nanomaterials, such as Carbon Nanotubes (CNT) and Quantum Dots (QDs), opens the doors for many potential improvements in luminescent systems and notably Optical Wireless Communication (OWC) systems. Other side, Cu2CdSnS4 quaternary alloy nanostructure has attracted attention in solar cell applications owing to the high optical absorption in visible range. This work presents the feasibility of the infrared uplink Visible Light Communication (VLC) system using Near Infrared Light Emitting Diode (NIR-LED) operating at 780 nm. The used NIR-LED-based Cu2CdSnS4 quaternary alloy nanostructure is to investigate the performance of NIR uplink transmission according to Line of Sight (LOS) channel model. In this transmission, the effect of transmitter orientation and transmitted optical power level with respect to Tx–Rx​ uplink distance are taken into consideration. For this purpose, performance evaluation will be achieved in terms of Bit Error Rate (BER) where we demonstrated satisfactory BER performance (BER≥10−9) over the entire typical room configuration. In addition, an optimal semi-angle interval and optimal Tx power level has been selected. We further investigated the performance improvement by using several transceivers, compared with a single one on the center of the ceiling.

Synergies between H, He and radiation damage in dual and triple ion irradiation of candidate fusion blanket materials

Three ferritic/martensitic alloys were studied to understand the synergistic effect between single ion beam (Fe2+), dual ion beam (Fe2++He2+ and Fe2++H+), and triple ion beam (Fe2++He2++H+) irradiations on cavity evolution. A commercial alloy, F82H, a castable nanostructured alloy, CNA3, and a high purity model alloy, Fe8Cr2W, were irradiated at 400°C to 600°C to a damage level of 50 dpa at a damage rate of 1 × 10−3 dpa/s with He and H injection rates of 10 and 40 appm/dpa, respectively. Post-irradiation characterization via bright field transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy was performed on all irradiated conditions to characterize the cavity size distribution and determine the effects of H/He injection on cavity microstructure. In all three alloys, hydrogen co-injection with helium resulted in an increased cavity number density and maximum cavity size, producing an increase in swelling over that from helium injection alone. Swelling in F82H appears to peak between 450°C and 500°C. At 600°C, swelling was minimal and cavities of high density and small size were confined to grain boundaries and dislocations while at 400°C, swelling is also low with a nearly homogeneous, high density, distribution of very small cavities throughout. Swelling was least in the commercial alloy F82H due to the high sink strength. The CNA3 alloy underwent dissolution of precipitates that lowered the sink strength and resulted in higher swelling than F82H, but less than the model alloy. Electron energy loss spectroscopy (EELS) elemental mapping revealed hydrogen forming a halo-like structure about the periphery of the cavities and helium residing within the cavities themselves. This observation suggests that hydrogen reduces the surface energy of helium-filled cavities which results in both increased cavity number density and cavity size in triple beam irradiation over dual beam irradiation.

Electrochemically co-deposited silicate sol–gel/PdAu alloy nanostructures and their application in electrocatalytic methanol oxidation

Electrochemically co-deposited silicate sol–gel/PdAu alloy nanostructures and their application in electrocatalytic methanol oxidation

Investigation of Structural and Mechanical Properties of Nanostructured TiMgSr Alloy for Biomedical applications

In this study, Nanostructured TiMgSr alloy is produced by cold Isostatic Pressing (CIP) followed by microwave sintering. The fabricated alloy results in the formation of solid binary solutions along with the elemental phases. The CIP compacted alloy was characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate the phases and the morphology. The presence of intermetallic phases SrTiO3 and Mg17Sr2 along with elemental Ti, Mg, and Sr crystallites with a narrow peak during the sintering process is prevalent; however, the crystallite size was retained in the nanoscale regime around 58 nm. The developed titanium alloy exhibits a low Young's modulus and good strength. The young's modulus of Ti–Mg–Sr alloys was around 48.11 GPa, significantly closer to human cortical bone (10–30 GPa). Among so far developed Ti-based alloys, the CIP consolidated Ti-Mg-Sr alloy results in low young modulus and hardness. In the future, it may be used practically for biomedical applications.

Gradient-structured high-entropy alloy with improved combination of strength and hydrogen embrittlement resistance

High-strength materials usually exhibit poor hydrogen embrittlement resistance, and thus, there are demands for materials with high strength and good ductility under hydrogen. Here, gradient structures containing surface nanotwins are introduced in a CrMnFeCoNi high-entropy alloy by surface mechanical attrition treatment, and hydrogen embrittlement resistance is compared with coarse- and nano-structured alloys produced by high-temperature homogenization and high-pressure torsion, respectively. The coarse-grained alloy shows high ductility, but its yield stress is low. The nanostructured alloy shows ultrahigh yield stress, but with poor hydrogen embrittlement resistance. The gradient-structured alloys have both high yield stress (500–700 MPa) and good ductility (15–33%) under hydrogen.

Pt-Based Multimetal Electrocatalysts and Potential Applications: Recent Advancements in the Synthesis of Nanoparticles by Modified Polyol Methods

In our review, we have presented a summary of the research accomplishments of nanostructured multimetal-based electrocatalysts synthesized by modified polyol methods, especially the special case of Pt-based nanoparticles associated with increasing potential applications for batteries, capacitors, and fuel cells. To address the problems raised in serious environmental pollution, disease, health, and energy shortages, we discuss and present an improved polyol process used to synthesize nanoparticles from Pt metal to Pt-based bimetal, and Pt-based multimetal catalysts in the various forms of alloy and shell core nanostructures by practical experience, experimental skills, and the evidences from the designed polyol processes. In their prospects, there are the micro/nanostructured variants of hybrid Pt/nanomaterials, typically such as Pt/ABO3-type perovskite, Pt/AB2O4-type ferrite, Pt/CoFe2O4, Pt/oxide, or Pt/ceramic by modified polyol processes for the development of electrocatalysis and energy technology. In the future, we suggest that both the polyol and the sol-gel processes of diversity and originality, and with the use of various kinds of water, alcohols, polyols, other solvents, reducing agents, long-term capping and stabilizing agents, and structure- and property-controlling agents, are very effectively used in the controlled synthesis of micro/nanoparticles and micro/nanomaterials. It is understood that at the levels of controlling and modifying molecules, ions, atoms, and nano/microscales, the polyol or sol-gel processes, and their technologies are effectively combined in bottom-up and top-down approaches, as are the simplest synthetic methods of physics, chemistry, and biology from the most common aqueous solutions as well as possible experimental conditions.

Combining synergetic effects of gradient nanotwins and nanoprecipitates in heterogeneous bronze alloy

Both strengthening effects of gradient nanostructure (especially the gradient nanotwins) and nanoprecipitates have been well-recognized to simultaneously improve the mechanical properties of metallic materials, e.g., the high strength–ductility synergy. In this study, a surface mechanical attrition treatment technique has been applied to fabricate a gradient nanostructured bronze alloy (Cu-12Sn-1.5Ni-0.6Fe) with pre-nanoprecipitates. Atomic-scale investigations were performed to capture the microstructural evolution governing the gradient refinement process along the depth direction of the treated alloy. On one hand, the body-centered cubic (bcc) Fe-rich pre-nanoprecipitates are found to be well-retained in the fabricated gradient nanostructured specimen. On the other hand, it is interesting to reveal that the semi-coherent interfacial zones between the bcc Fe-based nanoprecipitates and face-centered cubic (fcc) Cu matrix with the specific distribution of misfit dislocations could facilitate the nucleation and growth of gradient nanotwins along the depth direction. Specifically, the twinning partials could be associated with the dissociations of the misfit dislocations in the semi-coherent interfacial region, which is evidenced by the concomitant fcc-Cu/bcc-Fe/nanotwin triplex. As a result, the synergetic strengthening effects of gradient nanotwins and nanoprecipitates are combined to enhance the strength–ductility synergy and work hardening capacity. Moreover, in situ transmission electron microscope observations were conducted to understand the synergetic strengthening mechanisms of the gradient nanotwins and nanoprecipitates during the dynamic cracking process in the fabricated gradient nanostructured bronze alloy. The strategy of combining the nanoprecipitates and gradient nanostructure synergetic effects in our work might offer a novel pathway for designing high-performance metallic materials.

Void confinement and doping-modulation of IrNi alloy nanoparticles on hollow carbon spheres for efficient hydrogen oxidation/evolution reactions

Developing noble metal-based alloy nanoparticle (NP) electrocatalysts on solid supports with fast kinetics for alkaline hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is of considerable importance but remains a bottleneck for the potential applications of alkaline water electrolyzers and fuel cells. Herein, we design and implement a void confinement-mediated strategy to synthesize homogeneously distributed IrNi alloy NPs (4.23 nm in diameter) using nitrogen-abundant hollow carbon spheres (NHCSs) as the matrices. Attributing to the small nanostructured IrNi alloys, highly porous NHCSs with rich N-dopant, and the composition-tuned synergistic effect between Ir and Ni metals, the Ir2Ni8/NHCSs composite exhibits impressive electrocatalytic performances for HOR and HER, with an exchange current density of 246 A g Ir−1 in 0.1 M KOH and an overpotential of 54 mV at 10 mA cm−2 in 1.0 M KOH, respectively, outperforming the benchmark Pt/C and many reported noble metal-based electrocatalysts. The electrocatalyst also delivers favorable long-term stability for HOR and HER. The present study offers a feasible way to fabricate bifunctional electrocatalysts toward alkaline HOR/HER catalysis.

The effect of sink strength on helium bubble formation at elevated temperatures

In present study, the model Fe–9Cr alloy and two nanostructured ferritic alloys (NFAs) CNA1 and 9YWTV with high application potential in advanced nuclear power systems were selected to systematically investigate the effect of sink strength on helium bubble behavior at elevated temperatures. Helium bubble formation for a constant implanted He concentration of ∼7500 atomic parts per million (appm) was characterized using transmission electron microscopy (TEM) at 500 and 700 °C. A quantitative research and comparison of the influence for a specific sink strength on bubble formation was illustrated. Results showed that the introduction of nanoparticles into NFAs can effectively reduce bubble coarsening by sequestering the implanted helium into dispersed small bubbles due to the sufficient He entrapment by interfaces between the nanoprecipitates and the surrounding matrix. In addition, the NFAs with higher sink strength (9YWTV) revealed a higher suppression effects on bubble growth compared to general particle-free Fe–9Cr alloy and CNA1 with lower sink strength. This can be attributed to the comparable mean free path of He diffusion with the inter-particle distance for high particle density in 9YWTV. Meanwhile, the suppression effects of sinks on bubble growth decreased with increasing temperature from 500 to 700 °C. The sink strength of the order of 1015 m−2 and 1016 m−2 showed favorable suppression effect on bubble coarsening at 500 °C and 700 °C, respectively.

Superlative room temperature and cryogenic tensile properties of nanostructured CoCrFeNi medium-entropy alloy fabricated by powder high-pressure torsion

Attaining decent tensile properties in materials fabricated by conventional powder metallurgy (PM) techniques has perennially been a pivotal challenge due to structural defects— typically pores. This work fabricates a nanostructured CoCrFeNi medium-entropy alloy with an uttermost relative density of 99.63% through PM, i.e., cold powder consolidation using high-pressure torsion followed by annealing. The cold-consolidated sample showed outstanding tensile strengths of 2.06 GPa and 2.81 GPa at room and cryogenic temperatures, respectively, which was never achieved in PM-processed materials. The enhanced cryogenic tensile properties can be associated with intensive mechanical twin activities. Additionally, engineering the microstructure through subsequent annealing leads to a desirable synergy of tensile strength and ductility, which are highly sought after in structural applications. The present findings pave the way to fabricate the parts with superior tensile properties for cryogenic applications through a PM-based approach.

In Situ Monitoring of Scale Effects on Phase Selection and Plasmonic Shifts during the Growth of AgCu Alloy Nanostructures for Anticounterfeiting Applications

Tailoring of plasmon resonances is essential for applications in anticounterfeiting. This is readily achieved by tuning the composition of alloyed metal clusters; in the simplest case, binary alloys are used. Yet, one challenge is the correlation of cluster morphology and composition with the changing optoelectronic properties. Hitherto, the early stages of metal alloy nanocluster formation in immiscible binary systems such as silver and copper have been accessible by molecular dynamics (MD) simulations and transmission electron microscopy (TEM). Here, we investigate in real time the formation of supported silver, copper, and silver–copper-alloy nanoclusters during sputter deposition on poly(methyl methacrylate) by combining in situ surface-sensitive X-ray scattering with optical spectroscopy. While following the transient growth morphologies, we quantify the early stages of phase separation at the nanoscale, follow the shifts of surface plasmon resonances, and quantify the growth kinetics of the nanogranular layers at different thresholds. We are able to extract the influence of scaling effects on the nucleation and phase selection. The internal structure of the alloy cluster shows a copper-rich core/silver-rich shell structure because the copper core yields a lower mobility and higher crystallization tendency than the silver fraction. We compare our results to MD simulation and TEM data. This demonstrates a route to tailor accurately the plasmon resonances of nanosized, polymer-supported clusters which is a crucial prerequisite for anticounterfeiting.