Nanoscale metallic material composites consisting of bilayer and trilayer systems of two and three different metallic alternating layers show significant gains in hardness over monolithic single phase films. One of the main applications of these composites can be as protective coatings to technical components to increase their lifespan acting as a mechanical barrier to the carriers of permanent deformation. In this work, we study the strength of bilayer structures made of alternating layers of niobium (Nb) and copper–nickel (Cu–Ni) alloys. The effect of the layer size and composition on strength and hardening as well as the effect of the metal–alloy interface on the dislocation motion is investigated. The simulations reveal a close relationship between the atomic composition of the alloy and the hardening of the film. The results are also compared with experimental findings on nanopillars made of similar structures, and strong similarities are revealed and discussed.

Electropolymerization is a promising approach to produce thin films of active organic conjugated materials on a desired conducting substrate. In this work, an electropolymerization study has been carried out on two diketopyrrolopyrrole (DPP)-based monomers 2,5-bis(2-butyloctyl)-3,6-di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (BO-DPPF) and 2,5-bis(2-butyloctyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (BO-DPPT). These monomers consist of thiophene and furan heterocyclic moieties attached to a DPP core with a common solubilizing alkyl chain (butyl-octyl). The properties of these monomers were analyzed via differential scanning calorimetry, thermogravimetric analysis, UV–Vis spectrometry (UV) and photoluminescence. Cyclic voltammetry (CV) studies indicate the presence of irreversible oxidation and reduction reactions. The electropolymerization of BO-DPPF and BO-DPPT electron-deficient monomers to form polymer films on a glassy carbon electrode is achieved by applying a potential between −2 V and 2 V versus ferrocene for up to 50 cycles. The properties of the polymers were investigated using the cyclic voltammetry (CV) technique.

Metallic phase-change materials (PCMs) attract much attention due to their high thermal conductivity in thermal energy storage. Our previous work reported a kind of Cu@Cr@Ni bilayer capsules, which could endure at least 1000 thermal cycles between 1323 and 1423 K without leakage, and might be a potential high-temperature metallic PCM. This study numerically investigates the thermal energy charging performance of Cu@Cr@Ni capsules for recovering high-temperature waste heat at both constant and periodically fluctuant heat transfer fluid temperatures. It was revealed that only a short and slight sloped melting platform existed in the curve of outlet temperature due to the ultrahigh thermal conductivity of copper; with higher inlet velocities, the outlet and mean temperatures of such PCM increased and meanwhile the energy transfer efficiency decreased; the outlet and mean temperatures of the PCM and the liquid fraction in it were rather insensitive to the period of the inlet temperature fluctuation; and the amplitude of inlet temperature fluctuation, ±50 K, was sharply reduced to 5 K due to the thermal damping of the PCM.

The effect of specimen thickness on fracture toughness and fracture mechanism was investigated in bulk columnar-grained Cu with preferentially oriented nanoscale growth twins. Below a critical specimen thickness of ∼1.0 mm, plane stress state prevailed ahead of the crack tip and the fracture initiation toughness J C decreased with decreasing thickness. Above the critical thickness, J C decreased with increasing thickness until approaching an intrinsic thickness-independent value when the crack front was mainly under plane strain condition. Under plane strain condition, threading dislocations were majorly activated to glide along the nanotwin channels and to produce severe stress concentrations when they piled-up against grain boundaries (GBs). As a result, intergranular cracking mediated the failure of the nanotwinned Cu. On the contrary, under plane stress condition, dislocations slipping-transfer across twin boundaries (TBs) or partial dislocations gliding at TBs were activated to accommodate the plastic deformation. Consequently, stress intensification at GBs was plastically relaxed through enhanced detwinning and shear banding, which suppressed the intergranular fracture and promoted transgranular shear fracture.

The presence of interfaces and geometrical confinement can have a strong influence on the structure and morphology of thin films of semicrystalline polymers. Using surface-sensitive grazing incidence wide angle X-ray scattering and atomic force microscopy to investigate the vertical structure of thin films of poly(3-hexylthiophene) crystallized from the melt, we show that highly oriented crystallites are induced at the air/polymer interface and not as sometimes assumed at the interface to the substrate. These crystallites are oriented with their crystallographic a-axis perpendicular to the plane of the film. While the corresponding orientation dominates in thinner films, for sufficiently thick films (>60 nm) a layer containing unoriented crystals is present below the surface layer. Due to the anisotropic charge transport properties, the observed effects are expected to be of special relevance for potential applications of semiconductor polymers in the field of organic photovoltaics for which vertical transport in thicker films plays an important role.

We present a novel route to fabricate 3D nanoporous α-Ti foams by dealloying of TiCu master alloy in solid state using Mg powders. Pure open-cell nanoporous α-Ti foams are fabricated with BET surface area of 34.4 ± 0.8 m2/g and pore size in the range of 2–50 nm. The dealloying using powders is a solid state chemical reaction process to form Cu2Mg phase and Ti/Mg nanocomposites. The constituent of Cu in the TiCu alloy was dissolved into Mg powders thanks to the kinetics of interface reaction and volume diffusion. The pore-forming mechanism is a solid-state interdiffusion process. The ligament coarsening is from 492 to 650 nm with increasing of the dealloying temperature. The hardness and elastic modulus in nanoporous α-Ti foam follow linear decay fit with ligament size increasing. Our results demonstrate a facile strategy for the fabrication of nanoporous Ti foams with novel nanostructures and tailored properties.

This study investigates the synthesis, characterization, and corrosion behavior of AA6063 composites with the inclusion of micron-sized titanium carbide (TiC) particles with different weight percentages. AA6063/TiC particulate composites containing 0, 3, 6, 9, and 12 weight percent of TiC particles were produced by stir casting. The homogeneous dispersion of TiC particles in the AA6063/TiC composites was revealed from the scanning electron microscopy analysis. Energy dispersive X-ray spectroscopy analysis was conducted to ensure the presence of reinforcement particles in the matrix. Mechanical and corrosion properties of the produced composites are evaluated. The addition of TiC particles to the AA6063, the mechanical, electrical, and corrosion properties are initially increased and then decreased. Mechanical and corrosion study shows that the presence of 9 wt% of TiC particles in the matrix improved mechanical properties than other combination of TiC with the matrix material.

The oxidation behavior of nonstoichiometric Ti2AlC x (x = 0.69) powders synthesized by combustion synthesis was investigated in flowing air by means of simultaneous thermal gravimetric analysis-differential thermal analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscope/energy dispersive spectroscopy, with an effect of powder size. The oxidation of the fine Ti2AlC powders with the size of about 1 μm starts at 300 °C and completes at 980 °C, while with increasing the powder size around 10 μm the corresponding temperature increases to 400 and 1040 °C, respectively. The oxidation of nonstoichiometric Ti2AlC x (x = 0.69) powders is controlled by surface reaction in 400–600 °C, and mainly diffusion in 600–900 °C, with the corresponding oxidation activation energy of 2.35 eV and 0.12 eV, respectively. In other words, the critical temperature of changing oxidation controlling step is around 600 °C. The oxidation products were mainly rutile-TiO2 and α-Al2O3. The tiny white flocculent particles of α-Al2O3 appeared on the surface of fine Ti2AlC powders and increased with increasing the oxidation temperature.

We address the competitive precipitation and coprecipitation of three types of secondary phases, i.e., Cu-rich precipitates (CRPs), reverted austenite (RA), and alloyed carbide, in a high-strength low-alloy steel with austenite reversion treatment at 675 °C by using electron back-scatter diffraction, transmission electron microscopy, and atom probe tomography. There is a strong competitive diffusion of Ni and Cu participating in austenite reversion and Cu precipitation with the fact that no CRPs are detected in and around the RA. Meanwhile, there is also a strong competitive diffusion of austenite stabilizing element Ni and carbide-forming elements Cr and Mo into the pre-existing C-rich zone, leading to the formation of nonequilibrium alloyed carbide deviating from the stoichiometric composition. On the other hand, the alloyed carbide and CRPs provide constituent elements for each other and make the coprecipitation thermodynamically favorable. The knowledge on the interactive formation of these three features provides versatile access to tailor the distributional morphology of CRPs, RA, and alloyed carbide via a multistage heat treatment and thus realize their beneficial effect on strength and toughness.

We analyze the microscopic origins of subgap photoexcitations of individual gallium nitride (GaN) triangular cross-section nanowires (NWs), which are highly photoactive over a broadband spectral range. Using confocal hyperspectral photoluminescence (PL) microscopy, mid-gap states on the NWs were excited using subgap illumination, resulting in two distinct PL spectra corresponding to the polar (0001) and the semipolar $\left( {\bar 1101} \right)$ / $\left( {1\bar 101} \right)$ surfaces. Emission spectra are well represented by Gaussian functions with fitted centers of 1.99 ± 0.01 eV and 2.26 ± 0.01 eV, respectively. PL collected from the end facets exhibits interference fringes and a relative blue shift. Furthermore, the PL spectrum shifts strongly to the blue when the excitation intensity is increased. These observations are consistent with a qualitative model in which the PL results from excitation into a broad manifold of surface-associated states which are rapidly populated at a high excitation intensity and can couple to etalon modes via longitudinal photon emission.

A customized-built high-temperature tensile creep setup is introduced. Dog-bone shaped miniaturized specimens made from Nimonic-75 were tested as reference materials at temperatures of 850 and 1000 °C under constant load to verify the setup’s accuracy. The results were compared to tensile creep tests with conventional (standard size) specimens at identical experimental conditions. The shape of the creep curves obtained in the miniaturized specimens exhibits a pronounced minimum creep rate, thus, being seemingly different from the ones obtained for the bulk samples which reveal a clear steady-state regime. This is partly due to the continuous increase of stress under constant load testing conditions and very likely affected by the much higher surface to volume ratio of the miniaturized specimens leading to the premature onset of tertiary creep. Still, a good agreement was obtained between the two specimen sizes with respect to the dependence of the steady-state (standard size) and minimum (miniaturized size) strain rate on applied stress at various temperatures leading to also comparable activation energies of the creep.

The impact toughness and related microstructure of the dissimilar 9Cr/NiCrMoV welded joint fabricated by narrow-gap submerged arc welding were systematically investigated in the paper. Results indicated that the fracture appearance transition temperature (50% FATT) for weld metal was −11 °C, while low and scattered absorbed energies determined by different crack growth paths for the heat affected zone of 9Cr were gained which could not satisfy the requirement of service. However, a dramatically enhanced impact toughness was obtained by optimizing the post-weld heat treatment (PWHT) process. Microstructure characterization revealed that the microstructure evolution from martensitic laths in the previous PWHT metals to a softer ferrite matrix with the supersaturated carbon precipitating from the matrix led to higher toughness in the optimized PWHT materials. In addition, the observation of the fracture morphology found that the fractography varied from brittle fracture to a fracture mode with both brittle and ductile fracture feature with the change of crack growth paths in 9Cr-HAZ.

The aim of this study is to investigate the effects of different master alloys containing Ti, B, and Zr on the structure and tensile properties of thin-section A356 aluminum alloy in as-cast and T6-treated conditions. Microstructural examinations were performed using light optical and scanning electron microscopy. The results showed that the addition of 0.1 wt% Ti, 0.05 wt% B, and 0.1 wt% Zr decreases the average grain size of the cast alloy from 840 μm to 387 μm, 236 μm, and 363 μm, respectively. This structural refinement results in the variation of the α-Al primary phase distribution mode from dendritic to rosettelike. It has been found that 0.6 wt% Al–8B master alloy (0.05 wt% B) is the strongest to refine the structural parameters. This leads to the enhancement of both ultimate tensile strength and elongation values from 208 MPa and 6.2% in as-cast to 290 MPa and 12.5% in B-refined alloy at T6-treated conditions. In addition, the presence of more fine dimples on the fracture surfaces of the T6-treated specimens revealed that T6-treatment encourages ductile mode of fracture.

In the quest for high real in-line transmittances for transparent polycrystalline alumina (PCA), we need defect free processing. One of the biggest advances in producing high density defect free ceramics over recent years has been the advent of spark plasma sintering (SPS) or pulsed electric current sintering. The production of PCA with high transmittances >60% has been demonstrated, but the mechanisms behind this fast, pressure aided sintering method are still much debated. Here, we investigate the sintering of doped α-alumina powders using traditional and pulsed electric current dilatometry. We demonstrate that at the final sintering stage, there is no major difference in the sintering mechanisms between conventional sintering and SPS sintering. High densification rates occurring in SPS are shown to be related to powder reorientation at the very early sintering stage and viscous-flow dominated densification in the intermediate sintering cycle. This paper clarifies what parameters in the processing–sintering domain have to be improved for even higher real in-line transmittances for PCA.

Carbon–nitrogen compounds have attracted enormous attention because of their unusual physical properties and fascinating applications on various devices. Especially in two-dimension, doping of nitrogen atoms in graphene is widely believed to be an effective mechanism to improve the electronic and optoelectronic performances of graphene. In this work, using the first-principles calculations, we systematically investigate the electronic, mechanical, and optical properties of monolayer C3N, a newly synthesized two-dimensional carbon-graphene crystal. The useful results we obtained are: (i) monolayer C3N is an indirect band-gap semiconductor with the gap of 1.042 eV calculated by the accurate hybrid functional; (ii) compared with graphene, it has smaller ideal tensile strength but larger in-plane stiffness; (iii) the nonlinear effect of elasticity at large strains is more remarkable in monolayer C3N; (iv) monolayer C3N exhibits main absorption peak in visible light region and secondary peak in ultraviolet region, and the absorbing ratio between them can be effectively mediated by strain.

Microstructure and pitting corrosion behavior of base metal (BM), heat-affected zone (HAZ), and weld zone (WZ) in the 316L stainless steel weld joint was investigated. The results indicated that WZ, including ferrite and austenite phases, was mainly composed of columnar dendrites, while BM and HAZ exhibited a full-austenite structure with low Σ coincidence site lattice boundaries especially twin boundary primarily. No obvious pitting occurred in WZ, while the millimeter-scale pits were observed in HAZ and BM after immersion test in 6% FeCl3 solution. HAZ had a lower pitting potential than WZ and BM, while not much difference in pitting potential was observed between WZ and BM. Dendrite-selected corrosion occurred in WZ, while grain boundary was the preferable site for pitting corrosion in HAZ and BM. Gain refinement and a decrease in twin boundary volume fraction promoted the pitting corrosion susceptible of HAZ.

There is a need to discover new thermoelectric materials that can convert waste heat into electrical energy. In this paper, study has been done to observe the effect of shape and dimension of nanopores embedded in graphene nanoribbons (GNRs) as to tune their thermoelectric performance that can lead to enhancement of thermoelectric figure of merit (ZT). It is observed that incorporation of pores in GNRs greatly reduces the thermal conductivity. Although the Seebeck coefficient decreases with the introduction of the pore while the conductance depends upon the pore shape, the decreasing trend in thermal conductivity leads to enhancement of thermoelectric performance. The aim of this work is to study the effect of various circular and the triangular shaped dimensions so as to tune the pore to its optimal dimension that would enhance the overall thermoelectric efficiency. Ballistic transport regime and semiempirical method using Huckel basis set is used to obtain the electrical properties while the Tersoff potential is used for the phononic system.

The effects of alkaline earth strontium (Sr) additions on the microstructure and properties of Al–Si–Ge–Zn alloys and brazed joints were investigated. The results showed that the appropriate addition of Sr changed the morphology of β-GeSi phases from coarse needle-like to fine granular shapes effectively. Sr addition prevented the growth of Si by Sr adsorbing on the Si surface and caused the formation of many twins in Si. Sr addition had little impact on the melting temperature of the filler metals, but the spreading areas of Al–Si–Ge–Zn–xSr filler metals increased firstly and then decreased with the increase of Sr addition. In addition, the Sr addition optimized the microstructure of the brazed joints and improved the mechanical properties. Sound joints with high shear strength up to 152.4 ± 2.5 MPa could be obtained by applying Al–9.5Si–10Ge–15Zn–0.7Sr (all in wt%) filler metal.

Magnesium alloys with the lowest structural density exhibit unique applications in the automotive and aerospace fields. Rare earth addition is a promising method to enhance the mechanical properties of the Mg alloys. In the present study, the magnesium–aluminium (Mg–9Al) alloy containing varying wt% of gadolinium (Gd) is synthesized using the casting technique. The microstructure, mechanical, corrosion, and wear properties of the developed Mg–9Al–xGd alloy are evaluated and compared to the base Mg–9Al alloy. Microstructural investigation shows significant grain refinement and the presence of Al2Gd in addition to β-Mg17Al12 in the Gd-added alloys. Under tensile loads, the developed Mg–9Al–2Gd alloy exhibits enhancements in ultimate and yield strengths. The corrosion resistance of the alloys is found to increase with increasing Gd content and is optimal at 2 wt%. Considering the higher hardness and dispersity of the Al2Gd phase, Mg–9Al–2Gd has exhibited a higher wear resistance than that of the as-cast Mg–9Al alloy.