NiCr2O4/Cr2O3 system with ferrimagnetic spinel and antiferromagnetic transition metal oxide has been firstly synthesized by a chemical co-precipitation method. Magnetic measurements on this system also exhibit the exchange bias (EB) and training effect for the first time. EB effect with evident shift of coercive field and remnant magnetization can be detected at low temperature after field cooling from 350 K. The EB field can reach about 2037 Oe and the magnetization shift is as large as 0.129 emu/g at 10 K. Furthermore, EB effect recedes gradually with temperature increasing and disappears at about 70 K. In this process, EB field decreases with a linear dependence on the magnetization shift. This EB behavior is discussed according to the disordered regions existed at the interface between NiCr2O4 and Cr2O3. In addition, we have analyzed the training effect, which indicates the coexistence of two distinct forms of training mechanism during cycle procedure. One is concerned with an athermal impact resulting in the abrupt single cycle training and the other is gradual reduction of EB field during the subsequent cycles due to the conventional thermal activation mechanism.

A method based on the electroforming technique has been proposed for the fabrication of nanoparticle-reinforced copper-matrix composites using an electrolyte of copper sulfate–sulfuric acid solution containing 1 cm3/L of the nanoparticles without surfactants. Of the tested nanoparticles such as Al2O3, SiO2, TiO2, ZrO2, and CeO2, whose sizes ranged from 10 to 30 nm, only TiO2 nanoparticles were successfully embedded in the copper matrix during electroforming, owing to their positive charge in the electrolyte solution. It should be noted that there was very little contamination in the copper matrix, because surfactants were absent during electroforming. Therefore, the electrical conductivity of the specimen that was electroformed in the electrolytes with TiO2 nanoparticles was not significantly different from that of pure copper. Nevertheless, the hardness, yield, and ultimate tensile strength were significantly improved by a small amount (0.3 mass%) of TiO2 nanoparticles primarily because of strengthening by Orowan mechanics. The electroforming process is thus a promising means to prepare copper-matrix composites with an excellent balance of electrical conductivity and mechanical strengths.

Highly textured, ultrafine grain pure Bi2Te3 has been obtained by applying large-strain high-pressure torsion (HPT) to hot-pressed (HP) coarse grain material. Its thermal conductivity is significantly smaller than the conductivity of HP Bi2Te3, and its crystallographic texture and mechanical properties significantly improved. The mechanical properties of both, coarse grain and ultrafine grain, samples have been assessed by compression tests of 2 µm diameter micropillars machined by focused ion beam. The micropillars built from coarse grain samples are single crystalline, those built from ultrafine grain materials are an order of magnitude larger than their grain size. The test results put in evidence the elastic and plastic anisotropy of Bi2Te3 and the significant strengthening and toughening effect of ultrafine grain refining. For instance, after an equivalent strain of about 100, the Vickers hardness (in kg mm−2) increases from 60 to 120. Simultaneously, about a 40% reduction of the thermal conductivity has been measured, and a very strong basal texture is developed normal to the torsion axis. Such combination of properties looks very promising for simultaneously enhancing the thermoelectric figure of merit and the mechanical reliability of Bi2Te3-based alloys through HPT processing.

The study reports the functionalization of the size-controlled synthesized silver nanoparticles (AgNPs) with coumarin derivative. The size and the morphology of the as-synthesized AgNPs were obtained in the presence of glycerol and sodium citrate which acted as the reducing agent which led to nucleation of silver ions thus yielding different sizes of AgNPs. The obtained AgNPs were functionalized with different stoichiometric ratios of [HS-(CH2)11-NHCO-coumarin:HS-PEG-(CH2)11COOH] to form mixed monolayer protected silver clusters and their Raman activities were evaluated to determine the effect of particle size on the enhancement factor (EF). The functionalization and the stability of AgNPs were confirmed using a combination of techniques, namely UV–Visible spectroscopy, transmission electron microscopy, Zetasizer, and Raman spectroscopy. The obtained Raman spectra were used to calculate the EF of the HS-(CH2)11-NHCO-coumarin adsorbed on AgNPs, which was observed to increase with an increase in size of AgNPs from 16 to 30 nm. Increasing the particle size to 43 nm lowered the EF by 10-fold and hence an optimal size of ∼30 nm was achieved for the coumarin derivative adsorbate.

The Cu–Cr system alloys with different Ti contents were prepared and processed by deformation and heat treatment. The microstructures, mechanical, and electrical properties were investigated under as-cast and aged conditions. The results indicate that the Cr precipitates present a dispersed distribution and exhibit a face-centered cubic (fcc) structure rather than equilibrium body-centered cubic (bcc) structure in the initial stage of aging. A certain amount of Ti atoms dissolves in matrix due to the large solid solubility, while the remaining atoms segregate around the interface of the Cr precipitates to form a sandwich structure. Improvement of mechanical properties is achieved with Ti addition and the increasing rolling reduction, which can be ascribed to multiple mechanisms. In addition, Ti has a negative effect on the electrical conductivity, while deformation has a slight effect on conductivity.

Cast-iron (CI) based bulk amorphous alloy with compositions of Fe75.5−xC6.0Si3.3B5.5P8.7Cu1.0Alx (x = 0, 1 at.%) was synthesized by Cu mold casting. As indicated by increased critical diameters (dmax) for the amorphization, the substitution of Al enhanced the glass-forming ability of the alloy. However, the onset temperature of crystallization (Tx) and the range of supercooled liquid region (ΔTx) of the alloy decreased upon Al addition from 500 °C and 28 °C to 475 °C and 25 °C, respectively. It was revealed that the decreased thermal stability of the amorphous phase is related to the enhanced crystallization tendency to form primary α-Fe phase. Upon the nanocrystallization of primary α-Fe phase the Al-added alloy shows enlarged Ms of 176 emu g−1, still keeping a reasonable small Hc value of 0.086 Oe. The present study revealed that the minor Al addition enhances not only the glass-forming ability, but also the nanocrystallization behavior of the CI based bulk amorphous alloy.

Many self-healing polymers require elevated temperatures for healing. Curie temperature (TC) controlled magnetic nanoparticles can generate heat through the application of an external alternating magnetic field (AMF). Thus, heating can be localized and regulated, preventing damage to the polymer due to high temperatures. In this work, novel TC controlled magnetic nanoparticle filler–polymer matrix composites (Magpol) were investigated as wire insulation materials. Mn–Zn ferrites were introduced as the filler in a thermoplastic polyethylene vinyl acetate (EVA) matrix. The composite was subjected to different damage modes, such as chaffing and tear. Greater healing efficiency was obtained at lower filler loading compared to other relevant systems. Efficient healing was obtained without any thermal degradation. Good agreement was observed between experimental results and theoretical models of polymer healing. Thus, a Curie temperature controlled magnetic nanocomposite system was developed with improved self-healing capabilities.

Pristine multiwalled carbon nanotubes (P-MWCNTs) were functionalized with carboxylic groups (MWCNT-COOH) through oxidation reactions and then reduced to produce hydroxyl groups (MWCNT-OH). Pristine and functionalized MWCNTs were used to produce poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposites with 0.5 wt% of MWCNTs. MWCNT functionalization was verified by visual stability in water, infrared and Raman spectroscopy, and zeta potential measurements. Pristine and functionalized MWCNTs acted as the nucleating agent in a PHBV matrix, as verified by differential scanning calorimetry (DSC). However, the dispersion of filler into the matrix, thermal stability, and direct current (DC) conductivity were affected by MWCNT functionalization. Scanning electron microscopy (SEM) showed that filler dispersion into the PHBV matrix was improved with MWCNT functionalization. The surface roughness was reduced with the addition and functionalization of MWCNT. The thermal stability of PHBV/MWCNT-COOH, PHBV/P-MWCNT, and PHBV/MWCNT-OH nanocomposites were 20, 30, and 30 °C higher than neat PHBV, respectively, as verified by thermogravimetry analysis (TGA). Addition of pristine and functionalized MWCNTs provided electrical conductivity in nanocomposite, which was higher for PHBV/P-MWCNTs (1.2 × 10−5 S cm−1).

While conventional metallic glass (MG) is usually an alloy that contains at least two types of different elements, monatomic metallic glass (MMG) in body-centered cubic metals has recently been vitrified experimentally through ultrafast quenching. In this research, MMG in Ta was vitrified by molecular dynamics simulations and used as a model system to explore the atomistic mechanism of hardening in MG under cyclic loading well below the yield point. It was found that significant structural ordering was caused during the elastic cycling without accumulating apparent plastic strain, which ultimately led to the crystallization of MG that has been long conjectured but rarely directly proved before. It was also revealed that tensile stresses were more likely to induce structural ordering and crystallization in MG than compressive stresses.

Nanosized Al2O3 (Al2O3np) reinforced Al7075 composites were fabricated by specially made Al2O3np containing Mg powder and subtype multifrequency ultrasonic vibration. Compared to traditional techniques, Al2O3np was effectively dispersed in the matrix by the novel method. Microstructural studies showed that the addition of Al2O3np caused the grain refinement and that the resultant microstructures of composites depended on the dominant size and degree of Al2O3np clustering. The grain refinement could be mainly attributed to particle pushing mechanisms. Compared to the matrix alloy, the ultimate tensile and compressive strength of the as-cast composite with 1.5 wt% Al2O3np fabricated at 800 °C were increased by 59.6% and 42.6%, respectively. Transmission electron microscope analysis showed that high density dislocations and clear interfaces between particles and matrix were present in the grains, suggesting that the superior improvement of mechanical properties can be attributed to dislocation-type strengthening of matrix alloy and load transfer from matrix to hard nanoparticles.

Thermoluminescence (TL) and radioluminescence (RL) are reported over the temperature range 25–673 K from MgSiO4:Tb and MgSiO4:Eu. The dominant signals arise from the transitions within the Rare Earth (RE) dopants, with limited intensity from intrinsic or host defect sites. The Tb and Eu ions distort the lattice and alter the stability of the TL sites and the peak TL temperature scales with the Tb and Eu ion size. The larger Eu ions stabilize the trapped charges more than for the Tb, and so the Eu TL peak temperatures are ∼20% higher. There are further size effects linked to the TL driven by the volume of the upper state orbitals of the rare earth transitions. For Eu the temperatures of the TL peaks are wavelength dependent since higher excited states couple to distant traps via more extensive orbits. The same pattern of peak temperature data is encoded in RL during heating. The data imply that there are sites in which the rare earth and charge stabilizing defects are closely associated within the host lattice, and the stability of the entire complex is linked to the lattice distortions from inclusions of impurities.

M-type barium hexaferrite powders were synthesized using modified Pechini sol gel auto combustion method. The powder samples were heat treated at 900 °C for 5 h and were subjected to the structural, thermal, dielectric, magnetic, and optical studies. X-ray powder diffraction patterns show the formation of pure phase of M-type hexaferrite. Thermal analysis reveals that the weight loss of precursor becomes constant after 680 °C. The presence of two prominent peaks near 430 and 580 cm−1 in Fourier transform infrared spectroscopy spectra indicates the formation of M-type hexaferrites. The M–H curve has been used to study the magnetic behavior. The maximum value of coercivity is found for x = 0.41, which is higher than that of the pure barium hexaferrite. The band gap dependency on composition was studied using UV–Vis NIR spectroscopy. It was found that the dielectric constant is high at low frequency and decreases with an increase in frequency. Hexagonal structure of hexaferrite is visualized in transmission electron images.

Designing materials for performance in high-radiation fields can be accelerated through a carefully chosen combination of advanced multiscale modeling paired with appropriate experimental validation. The studies reported in this work, the combined efforts of six universities working together as the Consortium on Cladding and Structural Materials, use that approach to focus on improving the scientific basis for the response of ferritic–martensitic steels to irradiation. A combination of modern modeling techniques with controlled experimentation has specifically focused on improving the understanding of radiation-induced segregation, precipitate formation and growth under radiation, the stability of oxide nanoclusters, and the development of dislocation networks under radiation. Experimental studies use both model and commercial alloys, irradiated with both ion beams and neutrons. Transmission electron microscopy and atom probe are combined with both first-principles and rate theory approaches to advance the understanding of ferritic–martensitic steels.

Phase change materials are identified for their ability to rapidly alternate between the amorphous and crystalline phases and have large contrast in the optical/electrical properties of the respective phases. The materials are not only primarily used in memory storage applications, but also recently they have been identified as potential thermoelectric materials [D. Lencer et al., Adv. Mater.23, 2030–2058 (2011)]. Many of the phase change materials studied today can be found on the pseudo-binary (GeTe)1−x(Sb2Te3)x tie-line. While many compounds on this tie-line have been recognized as thermoelectric materials, here we focus on Ge4SbTe5, a single phase compound just off of the (GeTe)1−x(Sb2Te3)x tie-line, which forms in a stable rocksalt crystal structure at room temperature. We find that stoichiometric and undoped Ge4SbTe5 exhibits a thermal conductivity of ∼1.2 W/m K at high temperature and a large Seebeck coefficient of ∼250 μV/K. The resistivity decreases dramatically at 623 K due to a structural phase transition which leads to a large enhancement in both thermoelectric power factor and thermoelectric figure of merit at 823 K. In a more general sense, the work presents evidence that phase change materials can potentially provide a new route to highly efficient thermoelectric materials for power generation at high temperature.

Cu90Ag10 alloys were subjected to severe plastic deformation at temperatures ranging from 25 to 400 °C and strain rates ranging from 0.1 to 6.25 s−1 using high-pressure torsion. The deformed samples were characterized by x-ray diffraction, transmission electron microscopy, and atom-probe tomography. A dynamic competition between shear-induced mixing and thermally activated decomposition led to the self-organization of the Cu–Ag system at length scales varying from a few atomic distances at room temperature to ≈50 nm at 400 °C. Steady-state microstructural length scales were minimally affected by varying the strain rate, although at 400 °C, the grain morphology did depend on strain-rate. Our results show that diffusion below 300 °C is dominated by nonequilibrium vacancies, and by comparison with previous Kinetic Monte Carlo simulations [D. Schwen et al., J. Mater. Res.28, 2687–2693 (2013)], their concentration could be obtained.

The uniform Ag@AgBr core–shell microspheres were synthesized by a very facile wet-chemical route in aqueous solution, including a reduction process to prepare sphere-like Ag core and a deposition process to synthesize AgBr shell. X-ray diffraction, x-ray photoelectron spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy results confirmed the formation of Ag@AgBr core–shell heterostructures which had been achieved by this simple method. Field emission scanning and high-resolution transmission electron microscopy results of the as-synthesized Ag@AgBr composite revealed that AgBr particles were deposited on the surface of sphere-like Ag core. Under visible-light (λ > 420 nm) and real sunlight irradiation, the as-synthesized Ag@AgBr samples exhibit high activity and good stability for the photodegradation of Rhodamine 6G (R6G) in water. The present work suggests that the as-synthesized Ag@AgBr core–shell microsphere can be applied as a visible light-activated photocatalyst in efficient utilization of solar energy for treating water polluted by some chemically stable azo dyes in environment. The enhanced photocatalytic performance of the as-synthesized Ag@AgBr composite might be attributed to accelerated separation efficiency of electron–hole pairs on the interface of the Ag@AgBr hybrids and improved visible-light absorption abilities when AgBr is coupled with Ag.

The thermal conductivities of epoxy composites of mixtures of graphite and graphene in varying ratios were measured. Thermal characterization results showed unexpectedly high conductivities at a certain ratio filler ratio. This phenomenon was exhibited by samples with three different overall filler concentrations (graphene + graphite) of 7, 14, and 35 wt%. The highest thermal conductivity of 42.4 ± 4.8 W/m K (nearly 250 times the thermal conductivity of pristine epoxy) was seen for a sample with 30 wt% graphite and 5 wt% graphene when characterized using the dual-mode heat flow meter technique. This significant improvement in thermal conductivity can be attributed to the lowering of overall thermal interface resistance due to small amounts of nanofillers (graphene) improving the thermal contact between the primary microfillers (graphite). The synergistic effect of this hybrid filler system is lost at higher loadings of the graphene relative to graphite. Graphite and graphene mixed in the ratio of 6:1 yielded the highest thermal conductivities at three different filler loadings.

The joint of dissimilar metals between Mo2FeB2-based cermets and 316L stainless steel was welded by gas tungsten arc welding with no fillers. The weldability was investigated by plate rigid restraint cracking test and transverse rupture strength was measured by the three-point bending test. Microstructure of the weld joint was studied with scanning electron microscope, energy-dispersive spectrometer, X-ray diffractometer and differential scanning calorimeter, etc. Corrosion behavior was investigated by the potentiodynamic polarization test. Results revealed that weld solidification cracking susceptibility existed in the fusion zone. Coarse irregular complex ternary boride phase (M3B2) and hypoeutectic microstructure were formed in weld metal (WM). In heat affected zone (HAZ), a small number of M3B2 grains dissolved into the γ-Fe based binder, with growth and coalescence of the remaining M3B2 grains. Microhardness of HAZ increased slightly and WM presented the highest microhardness in the whole joint. Besides, potentiodynamic polarization test showed that WM had a better corrosion resistance than Mo2FeB2-based cermets, which can be attributed to the higher Cr content and relatively homogenous Mo distribution.

We report on the high catalytic activity of iron based metallic glass (MG) particles in dissociating direct blue dye (C32H20N6Na4O14S4) (DBD), a toxic water pollutant. We adopted high speed mechanical milling to activate the FeMG particles (of nominal composition Fe48Cr15Mo14Y2C15B6) and optimized the morphology and the particle size to achieve complete degradation of DBD in less than 20 min. The surface morphology and the particle size of the activated particles were characterized using scanning electron microscopy and transmission electron microscopy. They were found to have corrugated edge like catalytically active surfaces after mechanical activation. The dye degradation rate of the activated MG powder was characterized via UV–visible absorption spectroscopy. The rate of dye degradation was significantly faster for the activated particles (within 20 min), compared to both pristine FeMG particles as well as elemental iron particles. In addition, the dye degradation mechanism was studied using Raman and infrared spectroscopy. The catalytically activated surfaces are believed to break the –C–H–, –C–N–, and –N=N– bonds, resulting in complete degradation of DBD.

Hot compression tests were carried out on the duplex α + β leaded brass CuZn39Pb3 in temperature range of 600–800 °C and at strain rates of 0.001–1 s−1. A self-consistent model was used to analyze the flow behavior of the constituents and the material. A linear viscoplastic model was used to relate the flow stress of β and α + β composite to strain rate and the corresponding viscosity parameters were calculated at various deformation conditions. Using the viscosity parameters of β and α + β and the volume fractions of the constituents, the viscosity parameter of α was calculated. The values of the viscosity-like parameters and strain rate sensitivity for β and α + β composite were calculated using the nonlinear powerlaw viscoplastic equation. The results showed that the flow stress of α calculated using the self-consistent model was considerably higher than that of β. The difference could be attributed to the lower Zn content in α. The flow stress of α + β composite was calculated using the law of mixture rule. The law of mixture modeling of α + β composite for the iso-strain condition resulted to the overestimation of flow stress. The difference between the experimental and predicted results was attribute to the strain partitioning between α and β.