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γ-TiAl alloys have attracted interest as lightweight materials for structural applications at temperatures below 800 o C. With recent improvements in microstrutural control of the γ-TiAl alloys, resulting in excellent creep properties and high temperature strength, their use can be extended to temperatures higher than 800 o C. To increase their application temperature range, the oxidation resistance of γ-TiAl alloys must be improved through alloy design or coating techniques. To improve the high temperature oxidation resistance of γ-TiAl alloys, it is important to suppress the growth of TiO2 oxide by forming a dense coating layer to block oxygen atoms. In this study, we tried to improve the high temperature oxidation resistance of a conventional γ-TiAl alloy, Ti-48Al-2Nb-2Cr (Ti 4822) using a pack cementation process, with carbon sources and activating materials, XRD and EDS analysis results for the surface products indicated the formation of coating layers comprising oxides and carbides including TiC, Al4C3, Ti2AlC, and Ti3AlC. Based upon the sequential formation of coating layers and phase diagrams, the diffusion path of the carbon during the pack cementation process is proposed. Also, detailed carburization and oxidation behaviors of the γ-TiAl alloys in the temperature range of 800-1000 o C are discussed in terms of microstructural observations. Enhanced high temperature oxidation resistance was obtained in Ti-48Al2Nb-2Cr (Ti 4822) through a proper carbon pack cementation process.

Composites were prepared, through hot pressing, using carbon materials with different pore size distributions as additives for commercial Bi0.5Sb1.5Te3 thermoelectric material (BST, p-type). Thermoelectric properties of the composites were measured in a temperature range of 298‒473 K. Thermal conductivity of the composites, especially lattice thermal conductivity, was effectively decreased due to the mesoporous properties of the incorporated carbon additives. The electrical conductivity of the composites slightly decreased due to the electron scattering at the interface between the carbon material and the commercial BST matrix. The composite with 0.2 vol.% mesoporous carbon powder (36% mesoporosity) exhibited a figure of merit value approximately 10.7% higher than that of commercial BST without additives. This behavior resulted in 116% improved output power in the composite block-based single element compared with a bare BST thermoelectric block. The enhanced figure of merit was attributed to the effective reduction of lattice thermal conductivity by acoustic phonons scattering at the interface between the BST matrix and the mesoporous carbon as well as at the pore surfaces within the mesoporous carbon. By utilizing mesoporous carbon materials used in this study, the shortcomings and economic difficulties of the composite process with low dimensional carbon additives (carbon nanotubes, graphene, and nanodiamond) can be overcome for extensive practical applications. Mesoporous carbon powder with a tailored porosity distribution revealed the validity of bulk-type carbon additives to enhance the figure of merit of commercial thermoelectric materials.

Tin telluride (SnTe) overwhelmingly continues to be studied owing to its promising thermoelectric properties, tunable electronic structure, and its potential as an alternate to toxic lead telluride (PbTe) based materials. In this research, we engineer the electronic properties of SnTe by co-doping Mn and Bi below their individual solubility limit. The First principles density functional theory studies reveal that both Bi and Mn introduce resonance states, thereby increasing the density of states near the Fermi level leading to enhanced Seebeck coefficient. This unique combination of using two resonant dopants to introduce flatter bands is effective in achieving higher performance at lower temperatures manifesting into a large Seebeck value of ∼91 μV/K at room temperature in the present case. Both elements optimally co-doped results in a very high power factor value of ∼24.3 μW/cmK2 at 773 K when compared to other high performance SnTe based materials. A zT of ∼0.93 at 773 K is achieved by tuning the proportion of the co-dopants Mn and Bi in SnTe. The hardness value of pristine SnTe was also seen to increase after doping. As a result, synergistic optimized doping proves to be a suitable means for obtaining thermoelectric materials of superior characteristics without the need for heavy doping.

Nb1-xTixFe1.02Sb half-Heusler thermoelectric materials were synthesized trough arc melting and subsequent spark plasma sintering (SPS). Doping effect of Ti at Nb-site results in high power factor due to the optimization of hole carrier concentration. Further, the lattice thermal conductivity reduced as the Ti content increased, which mainly resulted from point defects and mass fluctuation by Ti doping as well as coherent nano-scale second phase, Ti-rich and Fe-deficient Ti1.18Fe0.57Sb. For the sample of Nb0.6Ti0.4Fe1.02Sb, a minimum lattice thermal conductivity of ∼2.08 W/mK was obtained. This is attributed to the enhanced phonon scattering at the alternating white and dark lamellar interphase boundaries of (Nb0.6,Ti0.4)FeSb half-Heusler and Nb-doped Ti1.18Fe0.57Sb. A maximum thermoelectric figure of merit, ZT, of ∼0.81 was obtained at 973 K, which is comparable with values previously reported for this system.

Amorphous alloys are being newly applied in wastewater treatment because of their unique atomic packing structure. They possess excellent degradation efficiency, stability and reusability. In this work, Fe80Si10B10 and Fe83Si5B8P4 amorphous ribbons exhibited advanced catalytic performance for the degradation of Methyl Blue (MB) and Rhodamine B (RhB) dyes, and the color removal reach nearly 100% within 11 min for both the dyes. Compared with the Fe80Si10B10 amorphous ribbon, the Fe83Si5B8P4 ribbon showed higher degradation efficiency due to its lower reaction activation energy, higher electron transfer ability and higher Fe content, and the formation of the galvanic cell between the strong Fe–P bonds and the weak Fe–B bonds. It also exhibited high stability and reusability. The degradation efficiency was improved when the appropriate concentration of H2O2 is added. As regards the pH, high degradation efficiency was observed in acidic MB solution, but it decreased as the pH increased up to pH 7. The application of the electro–Fenton–like process is discussed, which can effectively improve the degradation performance in a nearly natural solution. This study presents a high efficiency low-cost catalyst for synthetic dye degradation and expands the functional applications of Fe-based amorphous alloys.

An in-depth understanding of thermal behavior and phase evolution is required to apply heterostructured nanowires (NWs) in real devices. The intermediate status during the vaporization process of InAs NWs in an Al2O3 shell was studied by conducting quenching during in situ heating experiments, using a transmission electron microscope. The formation of As clusters in the amorphous Al2O3 shell was confirmed by analyzing the high-angle annular dark field images and energy-dispersive X-ray spectra. The As clusters existed independently in the shell and were also observed at the end of the InAs pieces obtained after quenching. The formation process of the As clusters was demonstrated from a theoretical perspective. Moreover, an ab initio molecular dynamics simulation (AIMD) was conducted to study the atomic and molecular behaviors.

A facile compositional tuning by Sb and Cu addition is performed to generate engineered defects in GeTe alloys with ultra-low thermal conductivity. Substitution of Sb and Cu at the Ge-site enhances the power factor due to the optimization of carrier concentration while maintaining the convergence of the valence bands. Furthermore, complex multi-dimensional defect structures including 0D (0-dimensional) substituted SbGe and CuGe, 2D twin and inversion boundaries, 3D herringbone structures, 3D embedded nanostructures, and 3D Cu-rich coherent precipitates are generated, which significantly reduce the lattice thermal conductivity benefitting from a collective phonon scattering. Due to this simultaneous manipulation of electronic and thermal transport properties, a maximum thermoelectric figure of merit (zT) of 1.4 was obtained at 723 K.

Coprecipitation effortlessly fabricated nickel hexacyanoferrate (NiHCF) with outstanding rate capability and stability for aqueous batteries. Citrate-aided coprecipitation decelerated the crystallization, assembling cubic-shaped powder based on separation between nucleation and growth. This study revealed that coprecipitation temperature determined the electrochemical performance. With lower temperatures, smaller particles with more water were formed by predominant nucleation, resulting in low crystallinity and capacity of 58 mAh g-1 . Expanded surface area reduced electrode/electrolyte interface charge-transfer resistance and showed excellent rate capability (79 % of initial capacity at 100 C-rate). However, poor cyclability was obtained. At elevated temperatures, nuclei growth and dehydration occurred, and thus highly crystalline large particles were formed. In turn, NiHCF delivered excellent capacity of 76 mAh g-1 at 1 C-rate but exhibited inferior rate performance because of longer diffusional path. Meanwhile, normal coprecipitation at 70 °C induced irregular-shaped tiny particles, presenting 93 % retention of initial capacity at 100 C-rate.

A transparent energy storage device is an essential component for transparent electronics. The increasing demand for high-power devices stimulates the development of transparent supercapacitors with high power density. A transparent electrode for such supercapacitors can be assembled via the electrophoretic deposition of an active material powder with a binder onto a transparent substrate. The properties of the binder critically influence the electrochemical behavior and performance of the resulting electrode. Ethyl cellulose (EC) is known as an eco-friendly, transparent, flexible, and inexpensive material. Here, we fabricated an electrode film with EC binder via electrophoretic deposition on an indium tin oxide (ITO) substrate instead of using the conventional polytetrafluoroethylene (PTFE) binder. The assembled electrodes with EC and PTFE were compared to investigate the feasibility of EC as a binder from different perspectives, including homogeneity, wettability, electrochemical behavior, and mechanical stability. The EC enabled the formation of a homogeneous film composed of smaller particles and with a higher specific capacitance compared with films prepared with PTFE. The annealing improved the adhesion strength of the EC because of its glass transition; however, its hydrophobic nature limited utilization of the active material for charge storage. Subsequent electrochemical activation improved the wettability of the electrode, resulting in an increased capacitance of 60 F g−1. Furthermore, even with the lower wettability of EC compared with that of PTFE, better rate performance was possible with the EC electrode. The increased mechanical stability after the annealing process ensured an excellent cycle life of 95 % capacitance retention for 15,000 cycles.

Over a period, there has been extensive research on both single and binary elements co-doping in SnTe. For the first time, we have investigated the effects of ternary dopants, Mn, Bi, and Sb, in SnTe with an aim of employing their synergetic effects to improve the Seebeck coefficient, consequently to increase the power factor and to lower the lattice thermal conductivity ( κ l a t ). Pristine SnTe exhibits a high electrical conductivity of 6320 S/cm, where after Mn isovalent and Bi and Sb aliovalent substitution at the Sn site, the electrical conductivity reduced up to 1530 S/cm at room temperature. As a result of the tuning of the carrier concentration, an increased Seebeck coefficient in all samples is observed. Compared to equivalent doping proportion of each dopant, a higher power factor of ∼22 μW/cmK2 is recorded. Stronger phonon scattering resulting from mass fluctuation in the multiple dopants, grain size, embedded nanostructures in the grain, and strained Mn–rich nano–precipitates in the grain boundary results in a low lattice thermal conductivity, with the lowest value recorded being ∼0.86 W/mK at 773 K. As a result, a ZT value of ∼1 at 773 K is recorded for the Sn0.85Mn0.09Sb0.035Bi0.025Te sample, which is a 271% improvement from our pristine SnTe.

Understanding the dynamic thermal behavior of nanomaterials based on their unique physical and chemical properties is critical for their applications. In this study, the thermal behavior of single-crystalline InAs nanowires in an amorphous Al2O3shell was investigated by conductingin situheating experiments in a transmission electron microscope. Two different thermodynamic patterns were observed during thein situheating experiments: (1) continuous vaporization and condensation simultaneously at temperatures lower than 838.15 K, and (2) pure evaporation at temperatures higher than 878.15 K. During the simultaneous condensation and vaporization in closer areas in a single InAs nanowire, the front edge of the vaporization was flat, while that of the condensation actively changed with time and temperature. Pure vaporization was conducted via layer-by-layer evaporation followed by three-dimensional vaporization at the final stage. The thermal behaviors of the InAs nanowires were demonstrated from a thermodynamic point of view.

Fe-based amorphous alloys have been found to be very efficient in the degradation of water pollutants due to their unique atomic arrangements with long-range disordered structure. In this work, Fe–B–C–Ti amorphous ribbons were successfully synthesized and showed high catalytic efficiency in the degradation of methylene blue (MB) under simulated sunlight and across a wide pH range. The catalytic efficiency was evaluated under different conditions to optimize the degradation performance. The amorphous ribbon Fe75B10C10Ti5 was found to exhibit the highest photocatalytic activity as explained by its optical and photoelectrochemical properties. It can degrade MB completely with low Fe-leaching and significant recyclability at pH close to a neutral range (pH 5). The degradation mechanisms can be explained in terms of photocatalytic activity along with the galvanic cell effect which contributed to the efficient MB degradation. This work provides a comprehensive idea for the synthesis of amorphous alloys by optimizing their elemental composition and also explains the catalytic activity of partially crystallized regions on the ribbon surface. The significant corrosion resistance and the quick degradation of MB in a wide pH range in a recyclable manner by these easily separable and highly efficient catalysts indicate great potential for their practical application.

We analyzed Zn-doped SnTe-based thermoelectric materials via transmission electron microscopy (TEM). The high-resolution TEM micrographs showed a doublet periodicity of the {1 1 1} lattice planes and the corresponding fast Fourier transform patterns revealed two sets of superstructure reflections having symmetrical intensity. The TEM results indicated the existence of a partially ordered CuPt-type structure in the Sn1–xZnxTe matrix; twinning bands were also observed in some regions.

Electronic structure is known to be highly influenced by the site occupancy and the stoichiometry of the material which in turn largely effects the thermoelectric properties. Herein, we present electronic calculations using density functional theory (DFT) of non-stoichiometric Ti doped NbFeSb configuration, showing the effect of the anti-site Fe atoms on the electronic properties, and supporting them with experimental results of the prepared Nb0.8Ti0.2Fe1+xSb1−x samples. The electronic structure of the non-stoichiometric sample shows the introduction of two distinct peaks near the Fermi level by the Fe atoms at the Sb sites. These resonance states are known to cause an increase in the density of states effective mass near the Fermi level, which explains the increase in the Seebeck coefficient in the sample x = 0.03 compared to the sample x = 0.00. In addition, a comparatively higher electrical conductivity is reported from sample x = 0.03, which is attributed to the aliovalent substitution of Sb atoms by Fe atoms. The simultaneous increase in the Seebeck coefficient and electrical conductivity culminates in an increased power factor of ∼50.3 µW/cmK2 at 373 K, which is ∼46% higher than that of samples x = 0.00 and x = 0.05, highlighting the possibility of increasing the power density by stoichiometric variation to achieve the high joule-per-dollar performance of NbFeSb-based TE devices, the relevance of which is also currently emphasized in the quest for commercial viability.

A novel nanocomposite structure comprising ~ 20-nm face-centered cubic Fe50Ni50 nanocrystals embedded within an amorphous matrix has been developed directly from a liquid alloy of Fe42Ni41.7C7Si4.5B3.9P0.9 (at%) through melt-spinning. Grain growth kinetics was significantly limited by the amorphous phase formed between nanocrystals. Glass forming elements rejected from nanocrystals stabilize the amorphous phase restricting further growth of nanocrystals. The nanocomposite ribbon exhibits excellent soft magnetic properties compared to those of the conventional micron-scale microstructured Fe50Ni50 alloy known as 50 Permalloy. When the as-melt spun ribbon was heated to 600 °C, two exothermic events occurred. The formation of metastable C-rich Fe3Ni and Si- and P-rich FeNi phases at low temperatures was confirmed by detailed transmission electron microscopy analysis. The hard magnetic behaviors of these metastable phases were estimated based on the hysteresis curve analysis results obtained from a ribbon heated to 600 °C. Through proper addition of glass-forming elements to FeNi-based alloys, nanocomposites with superior soft magnetic properties were effectively fabricated for massive practical soft magnetic applications.

Misch metal (Mm), consisting of Ce and La, was added to Ti–45Al–3Mo–2Nb alloys in order to investigate phase transformation and microstructural changes. The pseudo-binary phase diagram was estimated via PANDAT software™. The addition of Mm caused a decrease in both the fractions of α2/γ lamella and the β0 phase, and served as an important factor for a collapse of lamellar structures. In addition, Mm significantly decreased the colony size of the alloy, resulting in an increase in high-temperature tensile yield strength of ~ 40% for the alloys with 0.3 at% Mm at 800 °C. It appears that the addition of Mm affects the phase stability and increase the proportion of the γ phase. The microstructural changes, with respect to Mm additions, were discussed in terms of structural observations during isothermal heat treatments.

Iron nitrides composed of abundant and inexpensive Fe and N compounds such as α′′-Fe16N2 and γ’-Fe4N are in the spotlight as potential magnetic materials for the next generation of electric vehicles. Extensive applications of iron nitrides, however, have not been reported since their mass production is yet to be established. Due to the low solubility of nitrogen in liquid iron, the production of iron nitrides through conventional steelmaking processes is difficult. Moreover, α′′-Fe16N2 with a high saturation magnetization is known to be metastable and can form below 200 °C where diffusional phase transformations are slow. In this study, we propose a nonequilibrium process that can enhance the kinetics for iron nitride formation at low temperatures. Thermodynamically metastable Fe-based glassy alloy with a relatively open atomic packing structure was used as the starting material. Synthesis of iron nitrides during the mechanical alloying of Fe-based amorphous powders and solid nitrogen compounds was systematically studied to understand the mechanism of solid state nitriding reactions. In addition, thermal and magnetic properties were studied to provide a basis for practical applications of iron nitrides as rare-earth free magnetic materials.

The diffusion barrier layers in thermoelectric generators (TEGs) are widely used to improve their mechanical/thermal stabilities and energy generation performance; however, thickness dependence of diffusion barrier was rarely reported. In this study, we prepared Bi2Te3-based thermoelectric (TE) modules and Ni diffusion barrier with a thickness of 0–30 µm to investigate the correlation between the thickness of Ni layers and TE output performance. A TE module with 1 μm-thick Ni layer harvests a maximum output power of 2.79 mW under a temperature difference (ΔT) of 200 K, which is a higher value than that of a module without a diffusion barrier. Regarding the dependence of TE output performance on the diffusion barrier’s thickness, TEGs based on the thicker Ni layers showed lower output performance for all ΔT ranges compared with a 1 µm-Ni layer TEG. The degradation of TE conversion efficiency was related to the increment of contact resistance (Rc) with the thickness of the diffusion barrier. This Ni thickness-dependent Rc was explored using the transmission line method. The results from this study prove that the thickness of optimized diffusion barriers would maximize the output performance of TEGs, which could be used as a guide for improving the performance of TEGs.

Activated carbon, with its porous morphology and extremely high surface area, maintains the exclusive position as an electrode material in supercapacitors owing to its low manufacturing cost. Although its surface area can be boosted using a chemical etchant to create nanoscale pores, the use of chemicals requires a post-washing of the material to eliminate impurities. Herein, the activation of polyvinylidene chloride (PVDC) resin using ZnO chemical is described to prepare porous activated carbon materials for use as supercapacitor electrodes. During heat-treatment of a 1:1 mass ratio of PVDC resin:ZnO at 950 °C, activation and templating processes consecutively take place to produce porous carbon. Between 140 °C and 600 °C, ZnCl2 formed from the conversion of ZnO chemically activates the carbon with creating micropores. Above 800 °C, unreacted ZnO from the initial activation is reduced to Zn upon oxidation of the carbon with the additional micropore creation. Above 907 °C the Zn evaporates to leave activated carbon with no impurities. Through this process, the sites initially occupied by ZnO would turn to the pores by templating. With a rationally-designed ZnO ratio, porous carbon can be produced without washing. The activated carbon exhibits a high quinone content that reacts with H+ ions, with a high specific capacitance of 219 F g−1 in 1 M H2SO4 based on pseudocapacitance. However, the rate performance of this material is 55% due to the slow kinetics of the charge transfer reaction. On the contrary, a high quaternary-N content increases the rate capability of the material in 6 M KOH, where the double-layer mostly contributes toward charge storage.

Fe based amorphous alloys with high boron and gadolinium contents have been developed through a systematic alloy design technique for neutron shielding applications. Amorphous ribbons with the Gd content up to 10 at.% were prepared by a melt-spinning method and used as reinforcements within polyester matrix and concrete matrix, respectively. Excellent neutron shielding efficiency about 75% was obtained from the polyester hexahedron composites (5 cm × 5 cm × 1 cm) including only 1 vol% ribbon with the composition of Fe 72 B 15 Mo 3 Gd 10 . Moreover, a concrete composite (φ 10 cm × 5 cm thick) in which the amorphous ribbons with the composition of Fe 72 B 24.5 Mo 3 Gd 0.5 were uniformly distributed exhibited neutron shielding efficiency of around 86% demonstrating the applicability of amorphous ribbons as reinforcements in various composites for neutron shielding facility constructions.

Flexible thermoelectric-piezoelectric generator (f-TPEG) has emerged as the leading candidate to realize long-term biomedical monitoring-based ubiquitous healthcare services. We developed a f-TPEG composed of a piezoelectric (PE) poly(vinylidene fluoride-co-trifluoroethylene) thin film and thermoelectric (TE) bismuth telluride-based alloy blocks. The surficial properties of TE and PE components of f-TPEG were thoroughly optimized to minimize the loss of output performance and enhance the mechanical stability. The f-TPEG harvested a maximum electric voltage of ~17 V and current signals of ~3.8 μA at a temperature difference of 3 K by periodic bendings: The harvested output power of the fabricated hybrid energy generator was well integrated without sacrificing each PE and TE-based energy generation. In addition, to confirm the biological energy harvesting efficiency of the generator, we demonstrated the f-TPEG taped onto human fingers, which converts an output voltage of about 8 V and a current pulse of about 6 μA. The results obtained herein suggest that the f-TPEG would play a variety of important roles in wearable device, which needs long-term biomedical monitoring and applications in smart clothing.

We demonstrate the detrimental impacts of impurity phases on thermoelectric (TE) performance in Nb0.8Ti0.2Fe1.02Sb system that instigate performance irreproducibility that may impede rapid and progressive performance improvement of compounds synthesized by arc-melting. Three samples prepared by arc-melting are annealed at 700 °C, 850 °C and 1000 °C. The optimal homogeneity is achieved in the sample annealed at 850 °C with ~ 0.8 % impurity phases’ quantity, relative to ~ 4 % and ~ 10 % in the samples annealed at 700 °C and 1000 °C, respectively. The samples with increased impurities depict a significantly decreased Seebeck coefficient and increased lattice thermal conductivity, which intimately impairs the TE performance. The highest ZT is achieved in the sample with the least impurities, ~ 0.73 at 873 K, which is 49% higher than the inhomogeneous samples. This stresses the pertinence of minimizing the impurities in a bid to reproduce the optimal TE performance from this system.

Self-powered motion sensors have drawn many attentions for the last decade because it can be usefully applied to not only smart clothing and biomedical applications but also future remote controlling robotics systems. In this study, we develop a ceramic–polymer hybrid lead-free piezoelectric composite-based device to fabricate excellent flexible energy harvesters and kinetic motion sensing gloves. With the use of a composite composed of (K,Na)NbO3 (KNN) piezoelectric particles and poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] matrix, the fabricated flexible energy harvester generates an open-circuit voltage of ~5 V and short-circuit current of ~1 μA under mechanical bending deformations. Moreover, the advantages of the P(VDF-TrFE) matrix for piezoelectric composite-based devices are validated by the results of the finite element method (FEM) simulation. Based on the hybrid piezoelectric composite, stable and reliable self-powered kinetic motion sensors are fabricated to monitor tiny biomechanical motions, i.e., the angles of finger hinges and various hand gestures. Our development successfully indicates that the hybrid lead-free piezoelectric composite can be applied to the active component of self-powered kinetic sensors for future low-power electronic motion detector.

In the current study, phase stability of Ti-Al-Mo-Nb alloys was investigated, and the effect of B addition was examined for cast alloys. The fabricated cast alloys were mainly composed of α2 / γ lamellar with a β phase, when they were heat treated at 1100 °C followed by air cooling, the alloy was composed of α2 / γ lamellar with γ+β necklace phase at the colony boundary for the Ti-45Al-3Mo-2Nb-1B alloy, and the colony size was refined to ~ 20 μm. In order to identify the effect of the microstructures on mechanical strength, compressive tests were performed on the fabricated alloys of Ti-45Al-3Mo-2Nb and Ti-45Al-3Mo-2Nb-1B at room temperature and at 800 °C. The microstructural variations and phase stability were discussed in terms of pseudo-binary phase diagram calculated by Pandat software™.

The electromechanical properties of ternary InAsP nanowires (NWs) were investigated by applying a uniaxial tensile strain in a transmission electron microscope (TEM). The electromechanical properties in our examined InAsP NWs were governed by the piezoresistive effect. We found that the electronic transport of the InAsP NWs is dominated by space-charge-limited transport, with a I ∞ V2 relation. Upon increasing the tensile strain, the electrical current in the NWs increases linearly, and the piezoresistance gradually decreases nonlinearly. By analyzing the space-charge-limited I–V curves, we show that the electromechanical response is due to a mobility that increases with strain. Finally, we use dynamical measurements to establish an upper limit on the time scale for the electromechanical response.

Sublimation is an interesting phenomenon that is frequently observed in nature. The thermal behavior of InAs NWs with As-face polarity and the [1[combining macron]1[combining macron]1[combining macron]] growth direction of the zinc blende structure were studied by using in situ transmission electron microscopy (TEM). In this study, the anisotropic morphological and atomistic evolution of InAs nanowires (NWs) was observed during decomposition. Two specific phenomena were observed during the continuous heating of the NWs as observed using the TEM: the decomposition of the InAs NWs around 380 °C, much lower than the melting temperature, and the formation of particular crystallographic facets during decomposition. The low decomposition temperature is related to vaporization under the vacuum conditions of the TEM. The anisotropic decomposition of the InAs NWs during heating can be explained based on the polarity and the surface energy difference of the zinc blende structure of InAs. For example, the decomposition along the [111] direction (that is, the indium-atom-terminated plane) was continuous, resulting in a few high-index planes, for example, (022), (3[combining macron]1[combining macron]1[combining macron]), and (200), whereas that in the opposite direction (the [1[combining macron]1[combining macron]1[combining macron]] direction) occurred abruptly with the formation of ledges and steps on the (1[combining macron]1[combining macron]1[combining macron]) planes, accompanied by the generation of small grooves on the surface of the NWs. Finally, density functional theory calculations were conducted to understand the sublimation of the InAs NWs from a theoretical point of view. This study is meaningful that it provides an insight into the microstructural evolution of polar nanomaterials during heating by theoretical and experimental approaches.

In order to improve the performance of thermoelectric materials, nanoinclusions are often used to enhance phonon scattering. In this study, activated carbon, which is porous and thus has a large surface area, was incorporated in GeTe-based materials to cause increased boundary phonon scattering. Carbon dispersed in grain boundaries resulted in improved thermal properties without significant deterioration in electrical properties. Due to the extrinsic addition of activated carbon, the lattice thermal conductivity decreased by 13.8% on average. A maximum dimensionless figure of merit of 1.66 was achieved at 723 K for the Ge0.9Sb0.1Te composition with additional activated carbon.

For thermal neutron shielding applications, high boron amorphous ribbons with the compositions of Fe72-xB25-Mo3Crx (where x = 0, 5, 10, 15 or 20 at%) have been developed. From the morphological and compositional analysis of vein patterns formed on the fracture surfaces of the ribbons, the segregation of boron within shear band regions was identified and discussed with reference to “free volume concentration” and “temperature rise” models that had been proposed independently. High boron amorphous ribbons with optimum amounts of Cr exhibit excellent thermal neutron shielding efficiency in combination with mechanical properties such as tensile strength and bending flexibility. Moreover, corrosion resistance of the amorphous ribbons can be effectively enhanced through proper Cr additions, thereby expanding their structural applications in the nuclear industry.

Fe-based amorphous ribbons with excellent soft magnetic properties and mechanical properties were prepared in the Fe–Si–P ternary system. Enhanced soft magnetic properties could be achieved through annealing treatment of the ribbons for 1 h at 325 °C, which is far below the glass transition temperatures (462–474 °C). Icosahedral medium-range ordering with a size range of around 2 nm occurred throughout the amorphous matrix during the low-temperature annealing treatment. The annealed ribbons exhibited improved magnetic saturation of over 185 emu/g while maintaining good mechanical flexibility. During icosahedral ordering, the distance between the Fe atoms and the coordination number within the amorphous ribbon can be optimised for achieving high magnetic saturation. However, nanocrystallisation of the SiP and Fe2P transition phases embedded within the amorphous matrix occurred after the annealing treatment for 1 h at 385 °C, which caused deterioration of the soft magnetic properties and mechanical ...

The effect of minor Cu and Nb addition on glass-forming ability and nanocrystallization behavior of cast-iron-based bulk metallic glass was investigated. With simultaneous Cu and Nb addition, the crystallization kinetics of the amorphous alloys adequately modified to have enlarged initial nucleation rate and reduced growth rate of the primary α-Fe phase. However, due to the increased tendency to form secondary Fe 3 C and Fe 2 P phase, the cast-iron-based bulk metallic glass with combined Cu and Nb addition had a reduced processing window for nanocrystallization. Also, the simultaneous Cu and Nb addition decreased glass-forming ability of the alloy. Thus, it was revealed that the classical nanocrystallization strategy introducing combined Cu and Nb addition is not a suitable alternative to facilitate nanocrystallization of cast-iron-based bulk metallic glasses.

Soft magnetic Fe-based bulk metallic glass cylindrical specimens with a diameter of 2 mm and height of 6 mm have been successfully fabricated by selective laser melting (SLM) and the effect of scan speed v and laser power P on the microstructure, thermal stability and soft magnetic properties has been investigated. The results indicate that low v and high P lead to the formation of SLM samples with high relative densities, which can reach values of about 99.7%. This can be ascribed to the optimal energy transfer during processing at low v and high P. Structural and calorimetric studies prove that the SLM samples are fully amorphous. In addition, magnetic measurements reveal that the amorphous structure of the SLM material is identical to the parent atomized powders. Although additional work is required to remove the residual porosity and to avoid the formation of cracks during processing, the present results confirm that additive manufacturing by SLM represents an alternative processing route for the preparation of bulk metallic glass components with designed geometry having excellent magnetic softness. Keywords: Bulk metallic glasses, Selective laser melting (SLM), Soft magnetic properties, Microstructure

Phase formations during Si and B co-deposition by a halide activated pack cementation on Nb–Si–B alloys and the oxidation behaviors of the alloys were investigated together with diffusion pathway analysis. Coatings comprising Nb-borides and Nb-silicides were successfully fabricated on the surfaces of α-Nb, T2 single-phase and Nb ss + T2 two-phase alloys at 900 °C, respectively. For the coating process, powder mixtures with different Si to B ratios of (12.5:12.5) and (18.75:6.25) were used, respectively. Regardless of the Si to B ratio in the powder mixture used, the coating layers were identified as NbB 2 /NbSi 2 /Nb 5 Si 3 /substrate. The diffusion pathway followed the mass balance and showed one route regardless of the compositions of powder mixtures used in this study. The sequential oxidation product layers of the α-Nb and the T2 single phase alloy were identified as borosilicate/NbO 2 /NbB 2 /NbSi 2 /α-Nb and (borosilicate + 3Nb 2 O 5 ⋅B 2 O 3 )/Nb 2 O 5 /NbB 2 /NbSi 2 /T2, respectively. The diffusion pathway for the oxidation reaction was proposed using a schematic quaternary isothermal diagram.

Coatings with different porosities were prepared by controlling high velocity oxy-fuel process parameters. Pores were distributed homogeneously along the thickness of the coatings. Cavitation erosion rate of the coating was obtained by a vibratory cavitation equipment following ASTM G32 standard. As porosity of the coating increases, the cavitation erosion rate increases. Significantly high cavitation erosion rate was obtained in the early stage of the test for the coating with high porosity. As cavitation erosion test proceeds, the cavitation erosion rate tends to decrease. Cracks initiated in the surface pore area propagate along powder boundaries and merge to pores near surface. Due to the cracks, large coating parts consisting of a bunch of powders with good bonding were detached from the coating increasing the cavitation erosion rate. Corrosion products were preferentially formed on the pore areas enhancing the cavitation erosion rate. Consequently, pores near coating surface significantly accelerate the cavitation erosion rate through mechanical as well as chemical manners.

Molar volume modeling was performed for both Ti-Al-Nb and Ti-Al-Mo ternary systems based on the thermodynamic modeling of these two systems. Comparison between the calculated phase equilibria and the experimental data proved the accuracy of thermodynamic modeling. With the calculated density contour curves superimposed on the equilibrium phase diagram, it provides a map for alloy developers to identify the promising alloy compositions that satisfy both the phase stability and density requirements and rule out those that fail to meet the requirements.

The Fe based amorphous ribbons with the nominal compositions Fe84.2−xC11.0SixB3.9P0.9 (x = 4.5 and 13.5 at.%) were oxidized at low temperatures of 300 and 400 °C (i.e., well below the crystallization temperature) for 24 h in the air atmosphere. Significantly different oxidation kinetics between surfaces of the wheel side and the air side were observed, respectively. A continuous amorphous Si oxide layer with a few nanometers in thickness was formed on the air side surface of as-spun ribbon and effectively protected the ribbon from oxidation during annealing. However, discontinuity of the amorphous Si oxide layer was observed near casting defects on the wheel side surface. Moreover, due to low cooling rate near the casting defect regions, nanocrystals can be formed resulting in enhanced oxidation kinetics of the wheel side surface. As the annealing temperature is increased to 400 °C, the air side surface exhibited deteriorated oxidation resistance attributed to partial nanocrystallization of α-Fe. Nanocrystals of α-Fe formed on the surface acted as effective nucleation sites for the formation of iron oxides. Increasing annealing temperature leads to the increased thickness of both amorphous and crystalline oxide layers. However, effects of surface casting defects on the oxidation resistance can be significantly reduced by increasing the Si content.

Bulk quasi-ternary Fe80P13C7 (the real composition is Fe79.4Si1.0P12.8C6.8) glassy rod alloy with the maximum diameter of 1.0 mm was prepared by combining fluxing treatment and J-quenching technique using industrial cast iron and Fe–P alloys as raw materials. The result shows that the present Fe-based bulk metallic glass (BMG) exhibits good soft magnetic and mechanical properties with a high saturation magnetization of 1.43 T, a low coercivity of 7.2 A m−1 (for as-cast melt-spun glassy ribbon) and a high fracture strength over 2.75 GPa. The effects of fluxing treatment on the glass-forming ability (GFA), thermal stability, and magnetic properties of the present Fe-based amorphous alloy fabricated using industrial raw materials have also been investigated. It is indicated that the GFA of the present Fe-based alloy prepared using industrial raw materials is greatly improved through fluxing treatment, which should be attributed to the effective elimination of the impurities in alloy. In addition, soft magnetic properties of the present Fe-based amorphous alloy can be significantly improved by fluxing treatment, and the melt-spun glassy ribbon obtained from the fluxed mother alloy has a lower coercivity and higher Curie temperature compared with the melt-spun glassy ribbon obtained from un-fluxed mother alloy. The improvement in soft magnetic properties should be attributed to the purification of the master alloy through fluxing treatment, which results in more uniform atomic arrangement structure in the produced amorphous alloy.

The effect of minor Co and Ni alloying on soft magnetic properties and electrical resistivity of Fe 75.5 C 7.0 Si 3.3 B 5.5 P 8.7 (at%) bulk metallic glass has been investigated. Within examined compositional range (Co and Ni up to 4 at%, respectively), the saturation magnetization and electrical resistivity of the alloys continuously decrease with increasing Co or Ni content, while the Curie temperature and initial permeability increase. Comparing the effect of Co and Ni additions, the alloys with Co addition have much higher Curie temperature and saturation magnetization than the alloy with Ni addition. Also, the Co-added alloys show smaller coercivity and larger permeability than the Ni-added alloys. The present results suggest that minor addition of Co can provide better effectiveness to enhance the magnetic softness of Fe-based BMGs than minor Ni addition.

The influence of Cu on crystallization kinetics of Fe76.5−x C6.0Si3.3B5.5P8.7Cu x (x = 0, 0.5, and 1 at. pct) bulk amorphous alloys was investigated by isothermal and isochronal differential scanning calorimetry combined with X-ray diffraction. The thermal analysis revealed that the crystallization of the amorphous matrix proceeds through at least two exothermic events. The Cu-free glassy alloy forms by primary crystallization the metastable Fe23C6 phase, while upon 0.5 at. pct Cu addition the primary crystallized phase is α-Fe. The activation energy for crystallization, calculated using both Kissinger and Ozawa methods, decreases from about 500 kJ/mol to about 330 kJ/mol. Further increase of Cu addition to 1 at. pct promotes the concomitant crystallization of several phases, as α-Fe, FeB, Fe3C, and Fe2P. In order to understand the crystallization behavior of the alloys as a function of Cu content, the Avrami exponent n, evaluated from the Johnson–Mehl–Avrami equation, was in details analyzed. The current study reveals that the minor Cu addition plays a crucial role at the initial stage of the crystallization. Among the studied alloys, the glassy samples with 0.5 at. pct Cu addition have the optimum compositional condition for the single α-Fe formation with a high nucleation rate.

Nanocrystallization effect of primary Fe 23 M 6 -type phase (M: C or B) on magnetic properties of Fe-based bulk metallic glass (BMG) has been investigated. Under controlled microstructural modification with Fe 23 M 6 -type phase, the soft magnetic properties of Fe 76.5 C 6 Si 3.3 B 5.5 P 8.7 (at.%) BMG were significantly improved: saturation magnetization ( M s ) and initial permeability ( μ i ) of the alloy were dramatically enhanced from 1.35 T and 3500 to 1.57 T and 9890, respectively. The present study about introducing medium range atomic orderings and nanocrystallization of Fe 23 M 6 -type structure in amorphous matrix suggests a strategy to enhance the soft magnetic properties of ferromagnetic BMGs having the primary crystallized phase Fe 23 M 6 . This result provides useful insight to develop soft magnetic nanocrystalline materials, stating from BMG precursor with large glass forming ability.

The friction behaviors of bulk amorphous thermal spray coating (BAC) and second phase-reinforced composite coatings using a high velocity oxy-fuel spraying process were investigated using a ball-on-disk test rig that slides against a ceramic ball in an atmospheric environment. The surface temperatures were measured using an infrared thermometer installed 50 mm from the contact surface. The crystallinities of the coating layers were determined using X-ray diffraction. The morphologies of the coating layers and worn surfaces were observed using a scanning electron microscope and energy-dispersive spectroscopy. The results show that the friction behavior of the monolithic amorphous coating was sensitive to the testing conditions. Under lower than normal loads, a low and stable friction coefficient of about 0.1 was observed, whereas under a higher relative load, a high and unstable friction coefficient of greater than 0.3 was obtained with an instant temperature increase. For the composite coatings, a sudden increase in friction coefficient did not occur, i.e., the transition region did not exist and during the friction test, a gradual increase occurred only after a significant delay. The BAC morphology observations indicate that viscous plastic flow was generated with low loads, but severe sur- face damage (i.e., tearing) occurred at high loads. For composite coatings, a relatively smooth surface was observed on the worn surface for all applied loads. Keywordsamorphous thermal spray coating (비정질 용사 코팅), amorphous metallic matrix composite (비정질 기지 복합재료), friction characteristic (마찰 특성), sliding interface temperature (미끄럼 계면 온도)