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• The evolution and stability of a precipitate in a multi-component solution is studied. • The growth velocity and size of a precipitate are controlled by a growth factor. • The absolute and relative morphological stability criteria of the precipitate are shown. • The growth and stability of the precipitate are changed by adjusting the growth factor. • The interface kinetics enhances the stability of the precipitate. The growth and morphological stability of a precipitate in a multi-component solution with cross diffusion between solute species is studied by using the asymptotic method. The resulting asymptotic solution for the dynamics model of the precipitate reveals the relationship between precipitate growth and solute diffusion, and the absolute and relative stability criteria of the precipitate in the multi-component solution with cross diffusion between solute species. The absolute and relative stability radii of the precipitate are determined. It is demonstrated that the growth velocity and size of the precipitate in the multi-component solution are controlled by a growth factor that is determined by the solute diffusion coefficients. In the multi-component solution with cross diffusion between solute species, via the co-action between cross diffusion of solute species and interface kinetic undercooling, the precipitate enhances or reduces the morphological stability by changing the growth factor. In the multi-component solution, the interface kinetics decreases the growth velocity of the precipitate, and enhances the stability of the precipitate. When the interface kinetic undercooling is neglected, the absolute and relative stability criteria of the precipitate remain the same whether the diffusion of solute species is intrinsic or cross diffusive. [ABSTRACT FROM AUTHOR]

The infrared (IR) thermography diagnostic has recently been upgraded to achieve real-time temperature measurement and feedback capability in the experimental advanced superconducting tokamak (EAST). A new control and data acquisition program for IR camera is developed with online temperature calibration and compensation. Reflective memory (RFM) is configured in the data acquisition system for real-time data transmission to the plasma control system (PCS). Based on the upgraded IR thermography diagnostic, detachment plasma has been achieved for the first time in EAST with active temperature feedback. The divertor impurity seeding system is used to inject a sequence of short neon impurity pulses with 50% D2 to increase the edge radiation of the plasma particles. The temperature of the divertor target plates decreases to the preset target value and the divertor detachment has been realized with no serious reduction of plasma stored energy and confinement observed in the temperature feedback control phase. As a new feedback control method, the IR temperature feedback control shows great application prospects for the temperature and heat flux control of the first wall components in future long pulse operation of EAST. [ABSTRACT FROM AUTHOR]

• The effect of different initial morphologies to particle growth is studied. • The asymptotic solution shows the evolution of the particle with initial shapes. • The local undercooling in the concave interface favors particle growth. • The convexity of the non-spherical particle depresses particle growth. • The concavity of the non-spherical particle promotes particle growth. The effect of initial morphology on particle growth in an undercooled melt is studied in terms of an analytical approach. The growth of the particle is formulated as a dynamics model for the particle with different initial morphologies of concave and convex deformations. By using the asymptotic method, we solve the asymptotic solution of the dynamics model of the particle. The asymptotic solution reveals the effect of convexity and concavity of the initial shapes of the non-spherical particle on the temperature, concentration, and growth rate of the particle in an undercooled melt. The interface temperature in the concave part of the interface becomes higher than that in the convex part. The solutes are enriched near the concave part of the interface more than near the convex part of the interface. Compared with the convex part of the interface, the local undercooling and solute enrichment in the concave part of the interface facilitate the particle growth. The convexity of the particle depresses the particle growth, and the concavity of the particle promotes the particle growth. As the particle grows, the effect of initial morphology of non-spherical particles on particle growth attenuates, and the non-spherical particle tends to evolve into a spherical particle. [ABSTRACT FROM AUTHOR]

The morphological stability of dendritic growth from the binary alloy melt with an external flow is studied by means of the matched asymptotic expansion method and multiple variable expansion method. The uniformly valid asymptotic solution is obtained for the case of the large Schmidt number. The analytical result reveals that the stability of dendritic growth depends on a critical stability number above which dendritic growth is stable. The selection condition of dendritic growth determines the Peclet number, tip growth velocity, tip radius and oscillation frequency, which is significantly affected by the external flow. The stability mechanism of dendritic growth in the binary alloy melt with the external flow remains the same as that in pure melt. In the binary alloy melt with the external flow the solute concentration destabilizes the dendritic growth system. The numerical computation for various growth conditions demonstrates the variations of the critical stability number, tip growth velocity, tip radius, and oscillatory frequency with the undercooling, external flow and morphological number. [ABSTRACT FROM AUTHOR]

• The evolution and stability of a particle in a binary alloy melt is studied. • The critical nucleation radius in a binary alloy melt is determined. • Absolute and relative stability criteria of a particle in a binary alloy are shown. • Solute concentration first suppresses and then enhances the stability of the particle. • Minimum solute concentration for critical stability radius is determined. The evolution and morphological stability of a particle in a binary alloy melt is re-examined using the asymptotic method. The resulting asymptotic solution of the dynamics model of the particle reveals that the temporal evolution and morphological stability of the particle vary continuously as functions of solute concentration. In particular, (1) the critical nucleation radius of the particle in the binary alloy melt is determined. When solute is rejected from solid phase to liquid phase, the initial concentration increases the critical nucleation radius and depresses the growth velocity of the particle. When solute is incorporated into the solid, the initial concentration decreases the critical nucleation radius. (2) The absolute and relative stability criteria of the particle in the binary alloy melt are shown on the basis of Mullins and Sekerka's work in the pure melt. The critical stability radii for the absolute and relative stability criteria of the particle in the binary alloy melt are determined. The growth ratio of the critical stability radius to the critical nucleation radius in the binary melt does not exceed that in the pure melt. (3) When the segregation coefficient is less than one, with the growth of the particle, the initial concentration in the binary alloy melt first suppresses and then enhances the morphological stability of the particle. There exists a minimum solute concentration in the binary alloy melt such that when the initial concentration is lower than the minimum solute concentration, the stability of the particle decreases with the increase of solute concentration, whereas when the initial concentration is higher than the minimum solute concentration, the stability of the particle increases with the solute concentration. As the initial concentration increases, the critical stability radius first decreases to the minimum solute concentration at a certain solute concentration, and then increases with the solute concentration. This may control the morphological stability of particles by changing the addition of solute in the alloy melt. [ABSTRACT FROM AUTHOR]

• The growth of the particle in the alloy melt with the Soret diffusion is studied. • The approximately analytical solution is obtained by the asymptotic method. • The Soret diffusion markedly modifies the solute concentration distribution. • The Soret diffusion shows an amplification effect of growth velocity of the particle. The growth of particles in an alloy melt with the thermodiffusion is studied by using the asymptotic method. The resulting asymptotic solution for the dynamic model of the particle reveals that depending on the sign of the Soret coefficient, the solute concentration distribution is markedly modified and the growth velocity of the particle is increased or decreased. When the Soret coefficient is positive, as the growth velocity of the particle decreases, the thermodiffusion accelerates the decay of the particle, whereas as the growth velocity of the particle increases, the thermodiffusion accelerates the growth of the particle. As a result, the thermodiffusion presents an amplification effect of the growth velocity of the particle, being more significant in the early growth stage of the particle after nucleation. However, when the Soret coefficient is negative, as the growth velocity of the particle decreases, the thermodiffusion depresses the decay of the particle; as the growth velocity of the particle increases, the thermodiffusion depresses the growth of the particle. The thermodiffusion presents a reduction effect of the growth velocity of the particle accordingly. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogenated diamond-like carbon (DLC) was deposited using a radio-frequency plasma-enhanced chemical vapor deposition method. Electrical properties of Al, Au, Ti, and Zr contacts to nitrogen and boron doped DLC films have been studied, and mechanisms of the observed current–voltage (I–V) characteristics are investigated. Linear I–V characteristics were observed for Au, Ti, and Zr contacts to both nitrogen and boron doped DLC films. A band structure model for metal–DLC contact is proposed to explain the observed ohmic contacts. Fermi level shifting at the surface of DLC films produces an ohmic resistive layer instead of a Schottky barrier for metal–DLC contacts. Al contacts to both nitrogen and boron doped DLC films show nonlinear I–V characteristics, which are attributed to a dielectric layer of carbide (Al4C3) instead of a Schottky barrier suggested by other groups. Inert elements such as Au and Pt, and transition metals such as Ti, Zr and W, which form conductive carbides, are considered good contacting metals for electrical studies of DLC films. [Copyright &y& Elsevier]

Abstract: The present study aims to identify effects due to uncertainties in effective dynamic viscosity and thermal conductivity of nanofluid on laminar natural convection heat transfer in a square enclosure. Numerical simulations have been undertaken incorporating a homogeneous solid–liquid mixture formulation for the two-dimensional buoyancy-driven convection in the enclosure filled with alumina–water nanofluid. Two different formulas from the literature are each considered for the effective viscosity and thermal conductivity of the nanofluid. Simulations have been carried out for the pertinent parameters in the following ranges: the Rayleigh number, Ra f =103–106 and the volumetric fraction of alumina nanoparticles, ϕ =0–4%. Significant difference in the effective dynamic viscosity enhancement of the nanofluid calculated from the two adopted formulas, other than that in the thermal conductivity enhancement, was found to play as a major factor, thereby leading to contradictory results concerning the heat transfer efficacy of using nanofluid in the enclosure. [Copyright &y& Elsevier]

Abstract: We develop a new method to characterize the plastic deformation energy (PDE) of bulk metallic glasses (BMGs) using depth-sensitive nanoindentation. In this work, six BMGs with different ductility were investigated by measuring their PDE of the first pop-in events during loading. The PDEs of these BMGs are found to be closely correlated to their ductility. The ductile BMGs have smaller PDE values whereas the brittle BMGs have larger values. [Copyright &y& Elsevier]

Abstract: Aluminum 6092/(B4C)p metal matrix composites fabricated by two different powder consolidation routes, extrusion (EXTR) and sintering/hot isostatic-pressing (HIP), were made and tested over a wide range of strain rates (10−4 to (3×102)s−1) under tension. A tension-compression asymmetry of constitutive behavior is observed: the flow strength and ductility of these composites under tension are lower than those under compression. Such asymmetry is reinforcement volume fraction dependent, and the extent of asymmetry is larger for HIP composites. Fractographic observations show different interfacial bonding characteristics (good bonding for the EXTR composites and relatively weak bonding for the HIP composites), indicating a strong effect of interfacial debonding on the constitutive and failure behavior of these composites. TEM observations reveal a weak amorphous layer composed mainly of aluminum, magnesium and carbon along Al/B4C interface in the HIP composites, which is consistent with the experimental observations. [Copyright &y& Elsevier]

Phase transformations in a platinum modified nickel aluminide bond coat were investigated by in situ high temperature X-ray diffraction analysis. Three phases, L10 martensite, B2 (β-(Ni,Pt)Al) and L12 (γ′-Ni3Al), were identified at different temperature ranges. The martensite is stable at temperatures below 620 °C, and the β-phase is stable at elevated temperatures. The reversible transformation, M↔β, is the principal reaction occurring throughout the bond coat layer during thermal cycling. Quantitative measurements indicate that the molar volume of the β-phase is approximately 2% larger than that of the martensite. Finite element simulations incorporating the volume change associated with this transformation indicate that the transformation significantly influences the distribution of stresses and strains in TBC systems. The effect of the martensite on TBC life is sensitive to the transformation temperatures relative to the creep strength of the bond coat. [Copyright &y& Elsevier]

The thermal cyclic durability of a TBC is thought to be strongly dependent on the physical and mechanical properties of the bond coat layer. A novel high temperature microsample tensile testing technique has been employed to characterize the mechanical behavior of a platinum modified nickel aluminide bond coat at 0% and 28% of cyclic life in the temperature range of 25 to 1150 °C. Values for the coefficient of thermal expansion and the Young’s modulus are reported. The bond coat exhibits a ductile to brittle transition temperature at approximately 600 °C, and above this temperature the yield and creep strength decreases rapidly with temperature. A power law description of elevated temperature stress relaxation is developed. The intermediate temperature strength was found to increase with thermal cycling, while the high temperature strength remained the same. This evolution in properties has been related to the development of a martensitic transformation that occurs during each thermal cycle. [Copyright &y& Elsevier]

Microstructural evolution induced by thermal cycling in a platinum modified diffusion aluminide bond coat was investigated with transmission electron microscopy and elevated temperature X-ray diffraction (XRD). Before thermal cycling, the structure of the as-received bond coat was confirmed to be an ordered B2 phase, but significant lattice strains were found which were associated with the formation of a modulated structure. Thermal cycling resulted in significant changes in the microstructure of the bond coat. The compositional development assisted by chemical diffusion during thermal cycling has been related to the transformation of the bond coat from its original B2 structure to a Ni-rich L10 martensite. The L10 martensite was found to be stable at temperatures below approximately 600 °C and the B2 parent phase stable at elevated temperatures. Quantitative XRD measurements indicated that the volume of the B2 phase is approximately 2% larger than that of the martensite, which produces a ∼0.7% linear transformation strain. [Copyright &y& Elsevier]

Two newly developed integrated infrared and visible tangential wide-angle (WA) viewing systems (VS) have been mounted in the Experimental Advanced Superconducting Tokamak (EAST) to provide temperature measurement and hot spot monitoring of the plasma facing components (PFC) for machine protection and further physics studies of various plasma parameters such as the scrap-off layer power fall-off length λ q , the peak heat flux on the divertor target q p e a k etc. The systems use endoscopes with reflective optics to obtain a wide-angle view (49.5°×62°). Via endoscope, the 3-5 μm middle wave infrared camera and the visible camera with spectral range of 400−700 nm, the WAVS could provide simultaneous real time infrared and visible image data of the first wall components in the same field of view (FOV). Some key components e.g. the 4.6 GHz lower hybrid wave (LHW) antenna, the ion cyclotron resonance frequency (ICRF) antenna, the high field side region of neutral beam injection in port F, and approximately 78° more toroidal coverage of outer divertor regions with 27° more toroidal coverage of inner divertor regions are firstly covered by the camera system. This paper presents the diagnostic description of the newly developed WAVS and preliminary experimental results observed including fast-ion losses to the inner wall during neutral beam injection (NBI), single edge localized mode (ELM) observation on upper outer divertor, hot spots on antenna guide limiters and temperature and heat flux distribution on the tungsten and graphite divertor targets in EAST. [ABSTRACT FROM AUTHOR]

Examines a quasicrystalline phase discovered in a Zr[sub 65]Al[sub 7.5]Nu[sub 10]Cu[sub 12.5]Ag[sub 5] bulk metallic glass annealed in the supercooled liquid range. Electron diffraction patterns; Rotational symmetry; Formation of the phase by the addition of Ag; Relationship between Zr-based bulk metallic glasses and icosahedral quasicrystalline.

Describes the fracture surfaces of a nanocrystallized Zr[sub 65]Cu[sub 15]Al[sub 10]Pd[sub 10] metallic glass on an atomic scale with field ion microscopy. Propagation of cracks along the interfaces between nanocrystals and the amorphous matrix in the alloy with optimized microstructures.

Analyzes atom probe results on impurity oxygen dissolution in a nanocrystallized Zr[sub 65]Cu[sub 15]Al[sub 10]Pd[sub 10] metallic glass. Redistribution during nanocrystallization; Promotion of crystallization by impurity oxygen by forming metastable phases containing high content oxygen.

A method is proposed to measure the plastic deformation of thin metallic films on Si substrates induced by thermal cycling. The cross-sectional profiles of pattern-grown square Al films with a thickness of ∼250 nm and a size of ∼6 μmx6 μm were measured before and after thermal cycling by employing an atomic force microscope. With the assistance of statistical analysis, the change in the size and shape of the thin films were determined. Based on theoretical considerations, the thermal cycling deformation of thin films is attributed to creep and plasticity effects, accommodated by diffusion-controlled interfacial sliding. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Nano-scale phase separation and precipitation play a vitally important role in strengthening multi-component alloys, such as high entropy alloys (HEAs), which exhibit excellent physical and mechanical behaviors. Investigating their underlying atomistic mechanism is of great importance in understanding the strengthening mechanism of these complex alloy systems. In the present study, simplified atomic models have been developed to investigate the physical mechanism of the nano-phase separation in the fcc -based Al x CoCrCuFeNi HEAs at the atomic level. Furthermore, the modeling results agree well with the experimental observations from the state-of-the-art scanning transmission electron microscopy (STEM). [ABSTRACT FROM AUTHOR]

There is increasing interest in both relating the mechanical behavior of high-entropy alloys to their microstructural evolution and in their development for various applications. A special two-day international workshop on the above topic was held in Guiyang, China, in December 2014. The workshop gathered scientists and engineers to exchange information on recent progress in high-entropy alloys, to discuss the scientific issues and challenges to foster international collaborations, and to identify future directions. In this paper, a summary of this workshop is presented, including aspects of definition/terminology, phase formation, microstructure and phase stability, strengthening mechanisms, and high-temperature properties. Future research directions are also outlined. [ABSTRACT FROM AUTHOR]

The compatibility of efficient divertor detachment with high-performance core plasma is vital to the development of magnetically controlled fusion energy. The joint research on the EAST and DIII-D tokamaks demonstrates successful integration of divertor detachment with excellent core plasma confinement quality, a milestone towards solving the critical plasmaâ€"wall-interaction (PWI) issue and core-edge integration for ITER and future reactors. In EAST, actively controlled partial detachment with T et,div ∼ 5 eV around the strike point and H 98 > 1 in different H-mode scenarios including the high β P H-mode scenario have been achieved with ITER-like tungsten divertor, by optimizing the detachment access condition and performing detailed experiments for core-edge integration. For active long-pulse detachment feedback control, a 30 s H-mode operation with detachment-control duration being 25 s has been successfully achieved in EAST. DIII-D has achieved actively controlled fully detached divertor with low plasma electron temperature (T et,div â©˝ 5 eV across the entire divertor target) and low particle flux (degree of detachment, DoD > 3), simultaneously with very high core performance (β N ∼3, β P > 2 and H 98 ∼ 1.5) in the high βP scenario being developed for ITER and future reactors. The high- β P high confinement scenario is characterized by an internal transport barrier (ITB) at large radius and a weak edge transport barrier (ETB, or pedestal), which are synergistically self-organized. Both the high- β P scenario and impurity seeding facilitate divertor detachment. The detachment access leads to the reduction of ETB, which facilitates the development of an even stronger ITB at large radius in the high β P scenario. Thus, this strong large radius ITB enables the core confinement improvement during detachment. These significant joint DIII-D and EAST advances on the compatibility of high confinement core and detached divertor show a great potential for achieving a high-performance core plasma suitable for long-pulse operation of fusion reactors with controllable steady-state PWIs. [ABSTRACT FROM AUTHOR]

Hierarchical nanoporous metals with a large surface area and rich pore channels are the sought-after nanostructure for many applications. Here we report a two-step dealloying approach to fabricate a hierarchical nanoporous Ni alloy by utilizing the chemical stability difference of the constituent elements in a multicomponent precursor. Due to the large surface area and high electric conductivity, the hierarchical nanoporous Ni alloy exhibits a high specific areal capacitance of ∼1.11 F cm −2 and volumetric capacitance of 317 F cm −3 . [ABSTRACT FROM AUTHOR]

Abstract: We report an enzyme-modified nanoporous gold (NPG) biosensor with excellent sensitivity and selectivity towards the detection of glucose in the physiological environment containing common interferents. The internal surface of biocompatible NPG films is functionalized with glucose oxidase using thiols as linking molecules. The three-dimensional porous metal/organic hybrid electrode exhibits effective enzyme immobilization and peroxide detection on gold ligaments for amperometric glucose sensing. This study has important implications in developing NPG based metal/organic electrodes for electrochemical sensors with high selectivity and sensitivity. [Copyright &y& Elsevier]

Abstract: A serum tolerant polycation gene vector, G2 PAMAM-PGlu-G1 PAMAMs (ALA), was designed, synthesized, characterized and evaluated. A honeycomb-like molecular structure model for mechanistic explanation of ALA was postulated and discussed. Designed as a star-shaped polyamidoamine (PAMAM)-based polypeptide dendrimer through peptide bond linkages, ALA was with non-toxic low generation G2 PAMAM (G2) as its central core, polyglutamate (PGlu)s as its star-shaped backbone branches and G1 PAMAM (G1)s as its branch grafts and peripheral terminals. IR, 1H NMR demonstrated its successful combination. As a gene carrier, ALA exhibited good DNA binding and condensation capacity with particle size (∼87 nm for N/P 40, ∼170 nm for N/P 30) and ζ-potential (∼16 mV for N/P 30–40), negligible cytotoxicity, exciting serum tolerant capacity and significant serum-promoted (serum-containing 56.6%>serum-free 32.7%), cell line dependent (Hek 293 > Bel 7402 > Hela), incubation period dependent (38 h > 18 h > 12 h > 9 h > 4 h > 2 h > 1 h) and sustained (peak transfection appeared at 30 h incubation) transfection efficiency. The presence of serum had not only no inhibition on, but also prominent promotion to, the transfection activity of ALA. All above features differentiated ALA clearly from most other serum-inhibitive nonviral gene carriers, and proved ALA the promising and challenging potential efficient gene vector for practical clinical application. [Copyright &y& Elsevier]

New Au-based glassy alloys with high Au contents of ∼60–70at.% have been found to exhibit an ultralow glass transition temperature (∼66–86°C), a high glass-forming ability and a wide supercooled liquid region. They also have high thermodynamic and kinetic stability in the supercooled liquid state, strong oxidation resistance, good mechanical properties, very high corrosion resistance and excellent thermoplastic formability. [Copyright &y& Elsevier]

Abstract: Deformation twins and stacking faults have been observed in nanocrystalline Ni, for the first time under uniaxial tensile test conditions. These partial dislocation mediated deformation mechanisms are enhanced at cryogenic test temperatures. Our observations highlight the effects of deformation conditions, temperature in particular, on deformation mechanisms in nanograins. [Copyright &y& Elsevier]

The kinetics and mechanism of diffusionally accommodated interfacial sliding (interfacial creep) under far-field shear and normal stresses was studied, based on diffusion-bonded Al-Si-Al sandwich specimens. A previously developed interfacial creep law [Funn and Dutta, Acta Mater 1999; 47: 149], which proposed that interfaces may slide via interface-diffusion controlled diffusional creep, was experimentally validated by carrying out a systematic parametric study. In agreement with the model, the Si-Al interfaces slid via diffusional creep (n = 1) under the influence of an effective shear stress, which depends on the far-field shear and normal stresses, as well as the interfacial topography. Compressive stresses acting normal to the interface lowered the effective shear stress, resulting in a threshold effect, thus reducing the sliding rate. The rate of sliding was controlled by diffusional mass transport through a thin amorphous, O-rich interfacial layer, under the influence of local interfacial stress gradients, which arose due to the topological features of the interface. Instances of interfacial sliding in the absence of interfacial de-cohesion, which have been noted in composites, thin-film systems, etc., may be explained by the present mechanism, which also offers an alternative rationalization of threshold behavior during diffusional flow (besides interface-reaction control). [Copyright &y& Elsevier]

Solute effects on high-entropy alloys of equiatomic proportions are scientifically intriguing because there is no such well-defined "solute" and "solvent" atoms compared to those of conventional single principal element alloys. To date, most of the face-centered cubic alloys exhibit solid solution strengthening rather than softening due to the interactions between dislocations and solute atoms. Here, we present the careful experimental measurements and demonstrate solid solution softening, albeit weak, in a single phase CoCrFeMnNi through the minor addition of 2. at.% Al. This softening effect is mostly related to the decreased Peierl's stress by Al addition. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Structural characterization of dislocations and dislocation reactions in a face-centered cubic high entropy alloy was conducted using the state-of-the-art spherical aberration corrected transmission electron microscopy. We experimentally measured the stacking fault energy of the high entropy alloy from the atomic images and diffraction contrast of dislocation cores. The low stacking fault energy results in widely dissociated dislocations and extensive dislocation reactions, which leads to the formation of immobile Lomer and Lomer-Cottrell dislocation locks. These dislocation locks act as both dislocation barriers and sources and are responsible for the significant work hardening with a large hardening rate in the alloy. Based on the atomic-scale characterization and classical dislocation theory, a simple equation was derived to describe the work hardening behavior of the high entropy alloy in the early-stage of plastic deformation. [ABSTRACT FROM AUTHOR]

We report transmission electron microscope characterization of phase decomposition in a single-phase CoCrFeMnNi high entropy alloy (HEA) subjected to cold rolling and subsequent annealing at intermediate temperatures. It is found that plastic deformation plays a key role in phase destabilization of the HEA during intermediate annealing. The formation of Cr-rich precipitates in recrystallized grains and recovered samples suggests that dislocations generated by cold rolling is one of the critical factor leading to the destabilization of the stable HEA. Atomic-scale characterization of the Cr-rich precipitates reveals a complex crystallographic structure which is comprised of one-dimensional pentagons with selective atomic occupation. This study indicates that the phase stability of HEAs is very fragile at intermediate temperatures at which the multicomponent solid solutions stabilized by high configurational entropy may break down by local chemical disturbance at dislocations and grain boundaries. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys hold the potential for high-temperature applications beyond the capability of the state-of-the-art Ni-based superalloys, and thus, it is important to study their solid solution formation characteristics and mechanical properties. In this study, designed by CALPHAD method, formation of as-cast arc-melted body-centered cubic MoNbTaTiV was experimentally verified using X-ray diffraction and scanning electron microscopy. The measured density and lattice parameter for MoNbTaTiV are 9.29 g / c m 3 and 3.224 Å, which obey the rule of mixtures (ROM). The alloy exhibits high hardness at 443 Hv, high yield strength at 1.4 GPa, and good compressive fracture strength at 2.45 GPa with a fracture strain of ∼ 30 % at room temperature. The yield strength and hardness values of this alloy, and other single-phase refractory high-entropy alloys, are estimated using a simple model of solid solution strengthening. Reasonable agreement between modeling prediction and experiments is obtained. In addition, first-principles density functional theory calculations predict an enthalpy of formation of −0.865 kJ/mol for the MoNbTaTiV alloy, with calculated atomic volume and elastic properties (e.g., bulk and elastic moduli) obeying the ROM. [ABSTRACT FROM AUTHOR]

• An events detection and handling(EDH) algorithm based on hierarchical finite state machines in EAST PCS is designed. • The detection and handling of hot spots is incorporated into the exception handling system and simulated with the EDH algorithm. • The joint test method of Simulink and PCS is used to test algorithm for the first time in PCS. Experimental Advanced Superconducting Tokamak (EAST) is committed to long pulse high performance operation where plasma parameters will necessarily approach stability limits, which sets a higher demand on real-time events detection and handling (EDH). In order to enhance the current EAST plasma control system (PCS) events handling ability and explore a new intelligent scheduling mode for China Fusion Engineering Testing Reactor (CFTER) PCS, the EDH algorithm based on hierarchical finite state machines (HFSM) is designed in EAST plasma control system (PCS). The events and states in PCS were designed, and we successfully validated the state transition and algorithm scheduling. Moreover, a new event detection and processing for controlling hot spots of in-vessel components from hot spots is developed, and a simulation experiment is carried out in the closed-loop test environment between PCS and MATLAB/Simulink. The simulation results show that the EDH algorithm could capture the exception in time and implement effective strategies with the change of hot spots temperature. The temperature of hot spots were prevented from reaching a drastic situation, which proved the effectiveness of the EDH to protect the internal components of the device. [ABSTRACT FROM AUTHOR]

Face-centered-cubic (fcc) type high entropy alloys (HEAs) exhibit outstanding ductility even at the liquid nitrogen temperature, but they are relatively weak in strength which is far from the requirements for practical structural applications. One of the general concepts employed previously in alloy design is the suppression of ‘brittle’ intermetallic compound formation which usually leads to a serious embrittlement. Surprisingly, we reveal in this study that the precipitation of hard σ and μ intermetallic compounds tremendously strengthened the CoCrFeNiMo 0.3 HEA but without causing a serious embrittlement. It exhibits a tensile strength as high as 1.2 GPa and a good ductility of ∼19%. A careful study of the deformation behavior reveals that the fcc matrix exhibits an extremely high work hardening exponent of 0.75, which suppresses the propagation of microcracks originated at these brittle particles. Our work presents a very successful demonstration of using complex hard intermetallic particles to manipulate the properties of fcc-type HEA systems. Furthermore, lattice distortion has been carefully measured in powder-metallurgy materials by line broadening from X-ray diffraction (XRD). It is interesting to discover that lattice planes are highly distorted in HEAs and this distortion also contributes to solid solution hardening. [ABSTRACT FROM AUTHOR]

The formation of disordered solid solution in the hexagonal close-packed (hcp) structure in the GdHoLaTbY alloy and its mechanical properties were investigated in this study. The single hcp phase of the alloy in the as-cast state was confirmed by X-ray diffraction and scanning electron microscopy analyses. The compressive yield strength, fracture strength, and plastic strain of the alloy are 108 MPa, 880 MPa, and 21.8%, respectively, and the Vickers hardness is 96 HV. The results show that the yield strength, fracture strength, and hardness of the alloy obey the rule of mixture, which indicates that there is no hardening effect from entropy. Although the high entropy of mixing stabilizes the solid solution against intermetallic compounds, lack of severe lattice distortion from elastic strain or electronic interactions between principal elements impacts little on the mechanical properties. [ABSTRACT FROM AUTHOR]

Recent studies indicated that high-entropy alloys (HEAs) possess unusual structural and thermal features, which could greatly affect dislocation motion and contribute to the mechanical performance, however, a HEA matrix alone is insufficiently strong for engineering applications and other strengthening mechanisms are urgently needed to be incorporated. In this work, we demonstrate the possibility to precipitate nanosized coherent reinforcing phase, i.e., L1 2 -Ni 3 (Ti,Al), in a fcc-FeCoNiCr HEA matrix using minor additions of Ti and Al. Through thermomechanical processing and microstructure controlling, extraordinary balanced tensile properties at room temperature were achieved, which is due to a well combination of various hardening mechanisms, particularly precipitation hardening. The applicability and validity of the conventional strengthening theories are also discussed. The current work is a successful demonstration of using integrated strengthening approaches to manipulate the properties of fcc-HEA systems, and the resulting findings are important not only for understanding the strengthening mechanisms of metallic materials in general, but also for the future development of high-performance HEAs for industrial applications. [ABSTRACT FROM AUTHOR]

A free-standing nanoporous YNiCo metal/metal-oxide composite with hierarchical porosity is fabricated by chemically dealloying Al 85 Y 6 Ni 6 Co 3 metallic glass in alkaline solutions. The mixed core–shell-like metal/metal-oxide structure formed during dealloying due to the active properties of these metals. Time-dependent etching experiments suggest that the formation of large and small pores occur simultaneously, which may be related to the different dissolution rate of Al at different sites. The nanoporous composite with a highly conductive metal core exhibits a high areal capacitance. Moreover, this strategy can be extended to fabricate other nanoporous composites considering that the composition of metallic glass can be easily tuned. [ABSTRACT FROM AUTHOR]

Ceramics are known to be mechanically hard, chemically inert and electrically insulating for many important applications. However, they usually suffer from brittleness and have moderate strength that strongly depends on their microscopic structure. In this study, we report a size induced brittle-to-ductile transition in single-crystal aluminum nitride (AlN). When the specimen diameters are smaller than ∼3–4 μm, AlN micropillars show metal-like plastic flow under room-temperature uniaxial compression. The unprecedented plastic strain of ∼5–10% together with the ultrahigh strength of ∼6.7 GPa has never been achieved before. Transmission electron microscopy demonstrates that dislocations play a dominant role in the plasticity of the micro-sized AlN. [ABSTRACT FROM AUTHOR]

Using aerodynamic levitation, vitrification of a ternary Zr–Cu–Al alloy was observed in-situ by high energy synchrotron radiation X-ray diffraction in the temperature range from above the liquidus T liq to well below the glass transition temperature T g . The evolution of the atomic structure was studied using pair distribution functions (PDF) and molecular dynamic (MD) simulations. Vitrification was rendered possible due to the enhanced stability of the undercooled Zr–Cu melt after Al addition. Results indicate three regimes in the liquid alloy’s structural pathway to vitrification. Short (SRO) and medium range order (MRO) develop significantly during cooling the liquid phase to the glassy state. The rate of structural rearrangements is enhanced in the super-cooled liquid between T liq -140 K and T g . The populations of atomic clusters with icosahedral local symmetry become predominant as T g is approached and facilitate vitrification and suppression of crystal nucleation and growth. The scenario of a possible fragile to strong transition in the super-cooled liquid is discussed. [ABSTRACT FROM AUTHOR]

Nano-scale phase separation is reported in a nominal single-phase, high-entropy alloy (HEA), which was characterized using scanning transmission electron microscopy (STEM) combined with atom probe tomography (APT). Despite the fact that X-ray diffraction exhibits a single face-centered-cubic (fcc) phase feature of the as-cast alloy prepared by melt spinning, selected area electron diffraction reveals weak L 1 2 ordering in the as-spun alloy. High-resolution STEM shows the presence of two coherent nanophases with distinct L 1 2 and fcc structures, coupling with compositional segregations. The ordering of the L 1 2 domains is enhanced after annealing at 500 °C. Electron energy loss spectroscopy and APT analyses reveal that the L 1 2 nano-phase is enriched with Fe, Co, Cr and Ni, while the fcc domains are a Cu-rich phase. The nano-scale phase separation can effectively minimize the lattice distortions caused by the atomic size difference in the constituent elements, which may offer structural insights into the unusual mechanical behavior and phase stability of fcc HEA. [ABSTRACT FROM AUTHOR]

Ultrastable glasses and nanoglasses are two emerging materials with novel properties that have been investigated separately. In order to explore the combined effect of ultrastable character and a nanoglass with a nanoglobular microstructure on the kinetic behavior, the glass transition and crystallization behaviors of an ultrastable nanoglass and a melt-spun ribbon of Au-based metallic glass were examined by differential scanning calorimetry at heating rates ( ϕ ) of up to 40,000 K s −1 . The nanoglass shows ultrastable kinetic characters at low ϕ (e.g. 300 K s −1 ) and similar kinetic behaviors at high ϕ (e.g. 30,000 K s –1 ) compared to the melt-spun ribbon. The nanoglobular interfaces remain amorphous and appear to act as a kinetic constraint to induce a higher crystallization temperature compared to the melt-spun ribbon. The interface constraint effect disappears at 30,000 K s −1 . These results indicate that the nanoglobular microstructure can act to increase metallic glass stability and provide another mechanism for the synthesis of ultrastable glass. [ABSTRACT FROM AUTHOR]

We report for the first time the shear-induced local amorphization of boron suboxide subjected to nanoindentation. The amorphous bands have a width of ∼1–3nm and a length of 200–300nm along the crystal plane. We show direct experimental evidence that the amorphous shear bands of boron suboxide are driven from the coalescence of dislocation loops under high shear stresses. These observations provide insights into the microscopic deformation and failure of high-strength and lightweight ceramics. [ABSTRACT FROM AUTHOR]

Abstract: Nanoporous Ni with a tunable nanopore size and chemical compositions was fabricated by dealloying a Ni30Mn70 precursor alloy at various temperatures. The influence of electrochemical parameters on the formation of large-scale nanoporous Ni was systematically investigated. Different from the fabrication of nanoporous noble metals (Au, Pt and Pd), the dealloying of Ni30Mn70 includes three kinetically competitive processes: dissolution of Mn, interface diffusion of Ni and dissolution of Ni. The nanopore size and residual Mn can be tailored by controlling the dealloying time, temperature and applied potential. The as-dealloyed nanoporous Ni with a large internal surface area, excellent conductivity and naturally formed oxide surface can be directly used as a free-standing electrode for electrochemical supercapacitors with a high capacitance and excellent cycling stability. [Copyright &y& Elsevier]

Abstract: We report the influence of alloying elements (Ni, Al and Mn) on the microstructural evolution of Cu-rich nanoprecipitates and the mechanical properties of Fe–Cu-based ferritic alloys. It was found that individual additions of Ni and Al do not give rise to an obvious strengthening effect, compared with the binary Fe–Cu parent alloy, although Ni segregates at the precipitate/matrix interface and Al partitions into Cu-rich precipitates. In contrast, the co-addition of Ni and Al results in the formation of core–shell nanoprecipitates with a Cu-rich core and a B2 Ni–Al shell, leading to a dramatic improvement in strength. The coarsening rate of the core–shell precipitates is about two orders of magnitude lower than that of monolithic Cu-rich precipitates in the binary and ternary Fe–Cu alloys. Reinforcement of the B2 Ni–Al shells by Mn partitioning further improves the strength of the precipitation-strengthened alloys by forming ultrastable and high number density core–shell nanoprecipitates. [Copyright &y& Elsevier]

EAST has currently equipped with four wide-angle infrared (IR)/visible integrated endoscope diagnostics for routinely monitoring the status of plasma facing components (PFCs) and providing temperature information to ensure safe operation of the device. However, due to the existence of various sources of vibration force during the plasma experiments, image jitter can be clearly observed from the recorded IR videos, which increases the errors of temperature extraction from region of interest (ROI) within IR images and hence reduces the accuracy of heat flux calculation. In order to solve this problem, a method based on edge detection and phase correlation has been recently developed for correcting jitter of the IR videos on EAST, which has the advantages of high robustness, none accumulated error and high efficiency. Using this method, jitter of the IR video is successfully detected and corrected. Comparison between divertor heat flux results calculated from IR videos with and without jitter correction proves that the application of the edge-based phase correlation method for jitter correction can effectively improve the accuracy of the heat flux calculation. [ABSTRACT FROM AUTHOR]

Abstract: Dynamic shear punching is employed to process Zr36.6Ti31.4Nb7Cu5.9Be19.1 metallic glass matrix composites. A brittle fracture dominates during punchforming, and no macroscopic cracks or ruffles can be found, indicative of a good surface finish. The softening instability for metallic glasses happens once the yielding is available, avoiding the existence of shear bands and achieving smooth surfaces. No crystallization is accompanied in the heavy deformation zones during dynamic shear punching. The thickness of punched sheets for various BMG systems is highly dependent on the shear strengths. Furthermore, it is deduced that larger glass-transition temperatures of BMGs correspond to the thinner punched sheets, which provides a theoretical guidance to rapidly process metallic glass sheets. [Copyright &y& Elsevier]

Abstract: The evolution of precipitates in a Fe–2.5 Cu–1.5 Mn–4.0 Ni–1.0 Al multicomponent ferritic alloy during annealing at 500°C was systematically investigated by aberration-corrected scanning transmission electron microscopy. The atomic-scale structure and chemistry characterization reveal that primary precipitates with enriched Cu, Ni, Mn and Al originate from continuous growth of B2 ordered domains in the as-quenched alloy. The formation of a Cu-rich body-centered cubic (bcc) phase takes place by the decomposition of the B2 ordered primary phase, which forms a Cu-rich bcc core and ordered B2-Ni(Al,Mn) shell. The B2 shells serve as a buffer layer to moderate the coherent strain and to prohibit the inter-diffusion between the Cu-rich precipitates and bcc-Fe matrix, giving rise to a low coarsening rate of the precipitates. The Cu-rich precipitates experience a structural transformation from bcc to 9R at a critical size of ∼6nm during long time annealing, corresponding to obvious coarsening of the precipitates and dramatic loss in hardness of the alloy. [Copyright &y& Elsevier]

Abstract: In order to stabilize the supercooled liquid and enhance the glass forming ability of Al-based glass forming alloy, the alloying design based on minor Ca substitution for Al was examined to retard the precipitation of face-centered-cubic (FCC) Al. Calcium was selected as the alloying element, because it has a large negative mixing heating with Al but a positive value with the other components. This is anticipated to facilitate formation of Al–Ca clusters and then inhibit the diffusion of Al atoms which is thought to be the dominant reason that limits the glass forming ability (GFA) of Al-based alloys. The proposed strategy was confirmed in experiments by the observation of a greatly increased reduced glass transition temperature, T rg = T g/T l (T g the glass transition temperature and T l the liquidus temperature), the increased the activation energy for crystallization, and the increased activation energy for diffusion. The Al85−x Y8Ni5Co2Ca x (x = 0.5–5) system is found to possess extraordinarily high T rg = 0.613 far exceeding that for any known Al-based glass forming alloys. [Copyright &y& Elsevier]

Abstract: The structure and chemistry of nanoprecipitates in an oxide dispersion strengthened (ODS) 14YWT steel were systematically investigated by means of aberration-corrected scanning transmission electron microscopy. We found that the crystal structure of the nanoprecipitates depends on the particle size, while the compositional difference is insignificant. Large nanoparticles (∼10–30nm in diameter) have a long period NaCl-based structure including TlI-type stacking, while the small nanoparticles (<5nm) possess the NaCl-based structure with a high density of lattice defects. The size-related structural difference between small and large nanoparticles reveals the structural origins of the unusual thermal stability of the nanoprecipitates, as well as the extraordinary mechanical properties of ODS steels. [Copyright &y& Elsevier]

In situ measurements of the X-ray absorption fine structure for the supercooled liquid state of Au65Cu10.5Si17Ag7.5 bulk metallic glass, which exhibits extraordinarily low Tg and a stable supercooled liquid state, were performed. Analyses of data combined with molecular dynamics simulation suggest that the glass transition is caused by the breakdown of Cu–Cu bonding which connects Cu-centered icosahedral clusters. Cu atoms play a key role in the enhancement of glass formability and the low Tg of the Au65Cu10.5Si17Ag7.5 bulk metallic glass. [ABSTRACT FROM AUTHOR]