Showing papers in "Journal of Materials Research in 2019"

High-entropy alloys by mechanical alloying: A review

Abstract: Mechanical alloying (MA) followed by sintering has been one of the most widely adopted routes to produce nanocrystalline high-entropy alloys (HEAs). Enhanced solid solubility, room temperature processing, and homogenous alloy formation are the key benefits provided by MA. Spark plasma sintering has largely been used to obtain high-density HEA pellets from milled powders. However, there are many challenges associated with the production of HEAs using MA, which include contamination during milling and high propensity of oxidation. The present review provides a comprehensive understanding of various HEAs produced by MA so far, with the aim to bring out the governing aspects of phase evolution, thermal stability, and properties achieved. The limitations and challenges of the process are also critically assessed with a possible way forward. The paper also compares the results obtained from high-pressure torsion, another severe plastic deformation technique.

3-Dimensional graphene/Cu/Fe3O4 composites: Immobilized laccase electrodes for detecting bisphenol A

Abstract: Three-dimensional graphene (3D-GN)/Cu/Fe3O4 composite support materials were synthesized by a modified chemical reduction method using graphene oxide precursor. A 3D-GN/Cu/Fe3O4 biosensor was prepared by coating the electrode with laccase. The electrochemical properties of the biosensor were investigated by cyclic voltammetry (CV) and differential pulse voltammetry using potassium ferricyanide, phosphate-buffered saline (PBS) solution, and bisphenol A (BPA) solution. The current response of 3D-GN/Cu/Fe3O4 biosensors presents a remarkable sensitivity based on CV. The linear range of BPA is 7.2–18 µM using differential pulse voltammetry in PBS solution (pH = 4.0). A linear fitting equation of the laccase biosensor was observed for the current response as a function of BPA concentration. The detection limit was decreased to 1.7 µM. The detection approach herein turns out to be highly sensitive, has a wide linear range, and exhibits excellent stability.

A review on friction-based joining of dissimilar aluminum–steel joints

Abstract: This article showcases details on enumerative information of dissimilar aluminum (Al) to steel welds manufactured using different friction-based welding processes with an emphasis on the description of the manufacturing process, influence of parameters, microstructural variations, formation of intermetallic compounds (IMCs), and variations in mechanical properties. Friction-based welding processes such as friction welding, friction stir welding, hybrid friction stir welding, friction stir spot welding, friction stir spot fusion welding, friction stir scribe welding, friction stir brazing, friction melt bonding, friction stir dovetailing, friction bit joining, friction stir extrusion, and friction stir assisted diffusion welding are analyzed for the formation of dissimilar Al–steel joints. It can be summarized that friction-based joining processes have great potential to obtain sound Al–steel joints. The amount of frictional heat applied decides the type and volume fraction of IMCs that subsequently affects mechanical joint properties. Process variations and novel process parameters can enhance joint properties.

High-performance coaxial wire-shaped supercapacitors using ionogel electrolyte toward sustainable energy system

Abstract: Wire-shaped supercapacitors (WSSCs) hold great promise in portable and wearable electronics. Herein, a novel kind of high-performance coaxial WSSCs has been demonstrated and realized by scrolling porous carbon dodecahedrons/Al foil film electrode on vertical FeOOH nanosheets wrapping carbon fiber tows (FeOOH NSs/CFTs) yarn electrode. Remarkably, ionogel is utilized as solid-state electrolyte and exhibits a high thermal/electrochemical stability, which effectively ensures the great reliability and high operating voltage of coaxial WSSCs. Benefiting from the intriguing configuration, the coaxial WSSCs with superior flexibility act as efficient energy storage devices and exhibit low resistance, high volumetric energy density (3.2 mW h/cm3), and strong durability (82% after 10,000 cycles). Importantly, the coaxial WSSCs can be effectively recharged by harvesting sustainable wind source and repeatedly supply power to the lamp without a decline of electrochemical performance. Considering the facile fabrication technology with an outstanding performance, this work has paved the way for the integration of sustainable energy harvesting and wearable energy storage units.

First report on cold-sprayed AlCoCrFeNi high-entropy alloy and its isothermal oxidation

Abstract: Cold-sprayed high-entropy alloy (HEA) coatings have been generated for the first time. Mechanically alloyed (MA) AlCoCrFeNi powder was chosen as feedstock, owing to the extensive literature on this alloy. Coatings were synthesized under various gas temperature and pressure conditions. Isothermal oxidation was conducted at 1100 °C for 25 h on the coating cold-sprayed at 400 °C and 10 bar on a Ni-base superalloy substrate. The as-sprayed coating retained the MA phases and formed a protective alumina layer upon oxidation. An interdiffusion zone at the interface and unanticipated Mo diffusion from the superalloy substrate into the coating were observed after oxidation. A comprehensive characterization at the coating—substrate interface suggests that diffusion in HEAs is not sluggish. The factors governing the coating’s oxidation are elucidated, and a plausible oxidation mechanism is discussed. These studies are aimed at developing oxidation-resistant HEA coatings for potential applications at high operating temperatures.

Corn stover–derived biochar for efficient adsorption of oxytetracycline from wastewater

Abstract: Biochar conversion from corn stover was evaluated under various process conditions, and the absorption capacity of biochar was investigated for the removal of oxytetracycline in wastewater. Biochar was prepared at lower carbonization temperatures (200–500 °C) and was used in three different concentrations of chemical oxygen wastewater. The results showed that the biochar prepared at the temperature range of 200–500 °C had a faster sorption rate and shorter sorption equilibrium time compared to biochar produced at higher temperatures. The longest time to reach sorption equilibrium was 9 h for biochar obtained at 200 °C. However, the biochar prepared at 500 °C required only 0.5 h to reach the sorption equilibrium. The corn stover-biochar had the highest sorption capacity of 246.3 mg/g for oxytetracycline at 30 °C. The adsorption kinetics was consistent with pseudo–second-order kinetics. This study provides a theoretical basis for the conversion of corn stover into biochar as efficient sorbents.

Graphene synthesized in atmospheric plasmas—A review

Abstract: This article reviews the state of the art in the gas-phase synthesis of graphene in atmospheric plasmas. The substrate-free process involves the delivery of a carbon-containing precursor into a microwave-generated Ar plasma. Factors that influence the synthesis of graphene include precursor composition, reactor design, and the flow rates of gases. These factors have elucidated the mechanisms of graphene formation in atmospheric plasmas. Gas phase–synthesized graphene is pure and highly ordered and possesses unique features that make the material useful in applications such as catalysis, energy storage, lubrication, and the transmission electron microscopy imaging of nanomaterials. However, the main challenge in the synthesis process is the low rate of graphene production. This article anticipates future research aimed at overcoming this challenge and compares the atmospheric plasma method with contemporary graphene production techniques.

Synthesis, surface modification, and applications of magnetic iron oxide nanoparticles

Abstract: Magnetic iron oxide nanoparticles (MIONPs) are particularly attractive in biosensor, antibacterial activity, targeted drug delivery, cell separation, magnetic resonance imaging tumor magnetic hyperthermia, and so on because of their particular properties including superparamagnetic behavior, low toxicity, biocompatibility, etc. Although many methods had been developed to produce MIONPs, some challenges such as severe agglomeration, serious oxidation, and irregular size are still faced in the synthesis of MIONPs. Thus, various strategies had been developed for the surface modification of MIONPs to improve the characteristics of them and obtain multifunctional MIONPs, which will widen the applicational scopes of them. Therefore, the processes, mechanisms, advances, advantages, and disadvantages of six main approaches for the synthesis of MIONPs; surface modification of MIONPs with inorganic materials, organic molecules, and polymer molecules; applications of MIONPs or modified MIONPs; the technical challenges of synthesizing MIONPs; and their limitations in biomedical applications were described in this review to provide the theoretical and technological guidance for their future applications.

Dissimilar welding of Al0.1CoCrFeNi high-entropy alloy and AISI304 stainless steel

Abstract: High-entropy alloys (HEAs) have been proven to exhibit superior structural properties from cryogenic to high temperatures, demonstrating their structural stability against the formation of complex intermetallic phases or compounds as major fractions. These characteristics can find applications in nuclear and aerospace sectors as structural materials. As the dissimilar joint design is necessary for such applications, an attempt is made to fabricate the dissimilar transition joint between Al0.1CoCrFeNi-HEA and AISI304 austenitic stainless steel by conventional tungsten inert gas welding. Microstructural characterization by SEM and EBSD clearly revealed the evolution of columnar dendritic structures from the interfaces and their transformation to equiaxed dendritic grains as they reach the weld center. Also, considerable grain coarsening was observed in the heat-affected zone of the HEA. The tensile test results depict that the dissimilar weld joint showed significantly higher tensile strength (590 MPa) than the HEA (327 MPa), making it suitable for structural applications.

Magnetocaloric materials: From micro- to nanoscale

Abstract: Twenty one years ago, the discovery of the giant magnetocaloric effect (GMCE) at room temperature completely revolutionized the magnetocaloric materials field demonstrating the potential of magnetic refrigeration at room temperature and setting the beginning of a race for the best magnetocaloric material. Since then, hundreds of different bulk magnetic materials were studied in detail; however, only a small set of these exhibit GMCE. In the last ten years, the broad interest on these materials leads to the extension of their study to the micro- and nanoscale. In this review, we highlight the main motivations for exploring the size-reduction both from the technological and the purely scientific point of view and stress the general consequences on the magnetic and magnetocaloric properties. The emergence of different underlying mechanisms driving these effects will be identified with particular emphasis for the set of materials presenting GMCE.

Double perovskite (Sr2B′B″O6) oxides for high-temperature thermoelectric power generation—A review

Abstract: Recently, double perovskite-based oxide materials have been proposed for thermoelectric (TE) applications due to their environment-friendly nature, high-temperature stability, better oxidation resistance, and lower processing cost compared to conventional chalcogenides and intermetallics. In this review article, we have comprehensively summarized our recent research studies on Sr2B′B″O6-based double perovskites for high-temperature TE power generation. We have shown that decoupling of phonon-glass and electron-crystal behavior is possible in oxides by reducing thermal conductivity due to induced dipolar glassy state as a result of relaxor ferroelectricity. We have also introduced metal-like electrical conductivity (∼105 S/m) in these ceramics that are inherently insulator in nature. Moreover, we have observed interesting behavior of temperature-driven p–n type conduction switching assisted colossal change in thermopower in some of these oxides, hitherto, obtained only in chalcogenides. The charge transport mechanism in these complex oxides has been analyzed by small polaron hopping conduction model in conjugation with defect chemistry.

A green steam-modified delignification method to prepare low-lignin delignified wood for thick, large highly transparent wood composites

Abstract: To suppress the interface gap between the cell walls of wood and filled epoxy resin, a green and universal H2O2 or H2O2/HAc steam-modified delignification approach is developed to remove more lignin, thereby generating more pores to be more conveniently backfilled by epoxy resin for highly transparent wood composites. Utilizing the excellent penetration ability of steam, not only different wood species, such as basswood and pine, with different cutting directions but also the thickest (40 mm) and largest (210 × 190 mm) wood samples can be successfully delignified. Compared with the 1.9% lignin content (which is the normal content of delignified wood prepared by solution-based methods) of delignified wood, the as-prepared delignified wood has the lowest lignin content of 0.84% to date. After the infiltration of epoxy resin, not only did the mechanical strength of the 5-mm transparent wood composite increase from 12.5 to 20.6 MPa, but the transmittance (the wavelength was 550 nm) also increased from 80 to 87% due to the lower absorbance of visible light by lignin and the suppression of the interface debonding gap between the cell walls and the backfilled epoxy resin.

Effect of Gd 3+ doping on structural, morphological, optical, dielectric, and nonlinear optical properties of high-quality PbI 2 thin films for optoelectronic applications

Abstract: Herein, we present the fabrication and characterization of Gd:PbI2 thin films from low-cost material using a cost-effective spin-coating technique by taking the Gd content as 1.0, 2.0, and 3.0 wt% in PbI2. Single-phase and good crystallinity films oriented along the c-axis were confirmed by X-ray diffraction and FT-Raman spectroscopy. Size of crystallites increased with Gd concentration and was estimated to be in the range of 16–32 nm. Determination of morphology and size of grains (50–103 nm), and elemental confirmation were carried out by SEM/EDX analysis. Optical transparency of fabricated films was found to be in the range of 72–92%. The energy gap is reduced from 2.31 to 2.05 eV; this makes Gd:PbI2 films highly applicable in solar cells. The stable value of refractive index is estimated to be in the range of 1.85–2.3. Dielectric constant was observed to be reduced with doping and in the range of 2.5–35, and ac conductivity was also reduced by doping; however, both were enhanced with frequency. The values of χ(1), χ(3), and n(2) are found to be in the range of 0.15 to 2.5, 8 × 10−14 to 6.5 × 10−9, and 5 × 10−12 to 4 × 10−8, respectively.

Atomistic modeling of nanoscale plasticity in high-entropy alloys

Abstract: Lattice structures, defect structures, and deformation mechanisms of high-entropy alloys (HEAs) have been studied using atomistic simulations to explain their remarkable mechanical properties. These atomistic simulation techniques, such as first-principles calculations and molecular dynamics allow atomistic-level resolution of structure, defect configuration, and energetics. Following the structure–property paradigm, such understandings can be useful for guiding the design of high-performance HEAs. Although there have been a number of atomistic studies on HEAs, there is no comprehensive review on the state-of-the-art techniques and results of atomistic simulations of HEAs. This article is intended to fill the gap, providing an overview of the state-of-the-art atomistic simulations on HEAs. In particular, we discuss how atomistic simulations can elucidate the nanoscale mechanisms of plasticity underlying the outstanding properties of HEAs, and further present a list of interesting problems for forthcoming atomistic simulations of HEAs.

Chain rotation significantly reduces thermal conductivity of single-chain polymers

Abstract: Kevlar (polyparaphenylene terephthalamide) and PBDT (poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide))-derivatives have very similar chemical structures with aromatic rings. In this study, thermal conductivities of their single chains were calculated using molecular dynamics simulations. Chain rotation was found to be the key to reducing the thermal conductivity. By introducing a new chain rotation factor (CRF), we can easily quantify chain rotation level of single-chain polymers. We demonstrated that thermal conductivity decreases as the CRF increases. We performed further calculations on phonon properties and unveiled that the small thermal conductivity led by large chain rotation can be attributed to reduced phonon group velocities and shortened phonon mean free paths. Insights obtained in this study can be used for tuning thermal conductivity of various polymers and facilitating their various applications including thermal energy conversion and management.

Enhanced capacitive performance of activated carbon paper electrode material

Abstract: The activated carbon paper (ACP) has been designed as the active electrode material of supercapacitor to improve its capacitive performance. ACP is prepared by electrochemical nitrate ion–assisted exfoliation, sulfate ion–assisted exfoliation, and subsequent hydrothermal reduction processes. The as-prepared ACP shows obviously rougher surface along with the expanded layer distance. ACP exhibits higher specific capacitance of 380 mF/cm2 at 1 mA/cm2 than that of 21 mF/cm2 for carbon paper. ACP electrode shows the cycling capacitance retention of 98% after 5000 cycles at 10 mA/cm2. The symmetric ACP supercapacitor is constructed using ACP electrode and H2SO4 involved polyvinyl alcohol gel electrolyte. ACP supercapacitor presents the specific capacitance of 97 mF/cm2, the energy density of 0.343 mW h/cm3, and the output voltage of 1.6 V at 1 mA/cm2. ACP with high capacitance performance presents the promising supercapacitor application for the electrochemical energy storage.

Preparation and mechanical properties of selective laser melted H13 steel

Abstract: Process parameters (laser power and scanning speed) for H13 steel specimens produced by selective laser melting (SLM) are optimized, and microstructural characteristics and mechanical properties are investigated. The optimum process parameters are a laser power of 170 W and a scanning speed of 400 mm/s according to the maximum relative density of 99.2%. The microstructure consists of cellular grains and columnar crystal, which are composed of lath martensite and retained austenite, and there are no carbides or other second-phase particles present. The size of cellular grains is 1 µm. Compared with the common processed (forged and heat-treated) H13, SLM H13 has similar microhardness (561 HV) and tensile strength (1909 MPa) values. However, the elongation (12.4%) is a factor of ∼3 times higher and the impact energy (14.4 J) of the SLM specimen is somewhat lower. The relationship between the microstructure and mechanical properties is discussed. Fine grains and no second-phase precipitation determine the strength and plasticity of SLM samples.

CoCrFeMnNi high-entropy alloys reinforced with Laves phase by adding Nb and Ti elements

Abstract: Laves phase plays a positive role in improving the strength of high-entropy alloys (HEAs); Nb and Ti elements have potential to promote Laves phase formation in some HEAs. For improving the strength of the face-centered cubic (FCC) CoCrFeMnNi HEA, a series of (CoCrFeMnNi)100−xNbx (atomic ratio: x = 0, 4, 8, 12, 16) and (CoCrFeMnNi)100−xTix (atomic ratio: x = 0, 2, 4, 6, 8, 12) HEAs were prepared by melting. The effects of Nb and Ti on the microstructure evolution and compressive properties of the CoCrFeMnNi HEAs were investigated. For (CoCrFeMnNi)100−xNbx HEAs, the second-phase (Laves and σ phase) volume fraction increased from 0 to 42%. The yield strength also increased gradually from 202 to 1010 MPa. However, the fracture strain decreased from 60% (no fracture) to 12% with increasing Nb content. For (CoCrFeMnNi)100−xTix HEAs, the yield strength increased from 202 to 1322 MPa. The Laves phase volume fraction also increased from 0 to 27%. However, the fracture strain decreased from 60% (no fracture) to 7.5% with increasing Ti content. Addition of Nb and Ti has a good effect on improving the strength of FCC CoCrFeMnNi HEA.

Understanding the driving forces for crystal growth by oriented attachment through theory and simulations

Abstract: Oriented attachment (OA) is a particle-based crystallization pathway in which nanocrystals self-assemble in solution and attach along certain crystallographic direction often forming highly organized three-dimensional crystal morphologies. The pathway offers the potential for a general synthetic approach of hierarchical nanomaterials, in which multiscale structural control is achieved by manipulating the interfacial nucleation and self-assembly of nanoscale building blocks. Here, the current status of the development of a predictive theoretical framework for modeling crystallization by OA is reviewed. A particular emphasis is made on recent developments in understanding the microscopic details of solvent-mediated forces that drive nanocrystal reorientation and alignment for face-selective attachment. Interactions arising from the correlated solvent dynamics at particle interfaces emerge as the main sources of long-range face-specific interparticle forces and short-range torque for fine particle alignment into lattice matching configuration. These findings shift the focus of the experimental and theoretical research of OA onto the detailed study of interfacial solvent structure and dynamics.

Critical issues in conducting constant strain rate nanoindentation tests at higher strain rates

Abstract: Constant strain rate nanoindentation is a popular technique for probing the local mechanical properties of materials but is usually restricted to strain rates ≤0.1 s−1. Faster indentation potentially results in an overestimation of the hardness because of the plasticity error associated with the continuous stiffness measurement (CSM) method. This can have significant consequences in some applications, such as the measurement of strain rate sensitivity. The experimental strain rate range can be extended by increasing the harmonic frequency of the CSM oscillation. However, with commercial instruments, this is achievable only by identifying higher CSM frequencies at which the testing system is dynamically well behaved. Using these principles, a commercial system operated at the unusually high harmonic frequency of 1570 Hz was successfully used to characterize of the strain rate sensitivity of a Zn22Al superplastic alloy at strain rates up to 1 s−1, i.e., an order of magnitude higher than with standard methods.

On the mechanisms of stress relaxation and intensification at the lithium/solid-state electrolyte interface

Abstract: Under electrochemical cycling, stress intensification and relaxation within small volumes at the lithium/solid-state electrolyte (SSE) interface are thought to be critical factors contributing to mechanical failure of the SSE and subsequent short-circuiting of the device. Nanoindentation has been used to examine the diffusion-limited pressure lithium can support in the absence of active dislocation sources at high homologous temperatures. Based on the underlying physics of this deformation mechanism, a simple perturbation model coupling local current density, elastic stress, and diffusional creep relaxation is introduced. Combining this analysis with the indentation results, it is possible to describe a defect length scale which is too large for effective diffusional creep relaxation, but too small for efficient dislocation multiplication. In this instance, the properties of the SSE may become critical, and relevant indentation results of the SSE are described. The final outcome of the proposed analysis is a newly developed deformation mechanism map.

Alloying behavior and thermal stability of mechanically alloyed nano AlCoCrFeNiTi high-entropy alloy

Abstract: In this investigation, we have reported the alloying behavior, phase evolution, and thermal stability of equiatomic AlCoCrFeNiTi high-entropy alloy (HEA). The 40 h milled powder shows good chemical homogeneity with agglomerated particles varying in the range of ∼3–18 μm. The formation of a nanostructured single-phase BCC (a = 2.85 ± 0.01 A) was observed along with the minor tungsten carbide (WC) phase that formed due to contamination during milling. Thermal stability of the alloy has been studied using dynamic differential scanning calorimetry (DSC) thermogram and in situ X-ray diffraction. It has been found that this HEA is stable up to 600 °C (873 K). Consolidated samples at 1000 °C (1273 K) showed the transformation of body centered cubic (BCC) phase into the B2 (a = 2.87 ± 0.03 A) phase co-existing with minor hexagonal WC (a = 2.90 A, c = 2.83 A) phase.

Optimization of anti-solvent engineering toward high performance perovskite solar cells

Abstract: Anti-solvent treatment assisted crystallization is currently one of the most widely used methods to obtain high-quality perovskite films ascribed to its great operability. However, choosing a proper anti-solvent toward high-quality perovskite film for perovskite solar cells (PSCs) remains elusive. In this study, we qualitatively evaluate the impact of anti-solvent treatment on the grain growth and phase composition of perovskite by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectrometer, and UV-vis absorption measurement, etc. The results demonstrate that the chemical groups in anti-solvents also affect the formation of perovskites, and anti-solvents with a low boiling point and good polarity contribute to the superior efficiency and reproducibility of PSCs. The device prepared using ether as an anti-solvent exhibits the best power conversion efficiency of 18.47%. The results indicate a new path toward selecting an ideal anti-solvent to improve the performance of PSCs.

Double resonance Raman scattering process in 2D materials

Abstract: Raman spectroscopy is a fundamental tool for the characterization of two-dimensional materials. It provides insights into the electronic and vibrational properties of these materials and is particularly rich in features when the incident laser energy approaches the electronic energy transition of the material. Among these features, the double resonance Raman process provides important information on the electron, phonon, and electron–phonon properties. It was on the study of carbon-related materials that the double resonance bands sparkled showing their potential and, since then, have been deeply searched in the study of novel 2D materials. Here, the authors review the double resonance Raman process in 2D materials focusing on graphene and semiconducting MoS2 highlighting the origin of the bands mediated by the two-phonon and phonon–defect processes. The authors discuss the observed properties of the double resonance bands and compare the processes for graphene and MoS2 to find guiding principles for the appearance of double resonance bands. The authors also discuss the new findings of the intervalley scattering process in transition metal dichalcogenides. A brief discussion of the defect-induced bands in both materials is also presented.

Investigation of the flexural and thermomechanical properties of nanoclay/graphene reinforced carbon fiber epoxy composites

Abstract: Flexural and thermomechanical properties of the epoxy-based carbon fiber composites (CFCs) on addition of single and binary nanoparticles (nanoclay and graphene) have been investigated. It was found that nanoclay acts more effectively in increasing the stiffness of the CFCs, whereas graphene is more effective in achieving higher strength. Nanoclay-added samples exhibited highest flexural (64.5 GPa) and storage (25.3 GPa) modulus among all types. Graphene-added samples showed highest improvement (by 21%) in flexural strength and exhibited most stable thermomechanical properties with highest energy dissipation capability (3.1 GPa loss modulus) in flexural test and dynamic mechanical analysis (DMA), respectively. By contrast, addition of binary nanoparticles reduced the stiffness and significantly increased the strain to failure (42%) of the composites. Optical microscopy and scanning electron microscopy indicated that addition of nanoparticles significantly reduced delamination and matrix cracking of the CFCs because of strong interfacial bonding and toughened matrix, respectively.

Collagen and elastin scaffold by electrospinning for skin tissue engineering applications

Abstract: In recent years, tissue engineering has helped to reduce hospital stays and deaths caused by skin wounds. Scaffolds are one of the main factors that influence the success of any tissue graft. Collagen is one of the main components of the extracellular matrix, and there has been much interest in new sources for application as a biomaterial. In this work, a tissue engineering scaffold was developed using the electrospinning technique. The chicken skin was used as an alternative source to obtain collagen. The combination of this collagen with elastin was successfully electrospun, and a distribution of diameters was obtained, less than 100 nm. In vitro tests showed the adhesion and proliferation of the cells, as well as an absence of cytotoxicity from non–cross-linked scaffolds and scaffolds that were cross-linked with carbonyldiimidazole. The structure and composition of the developed scaffolding provide a favorable environment for cell growth and generating a skin substitute.

Microstructure and properties of CoCrNi medium-entropy alloy produced by gas atomization and spark plasma sintering

Abstract: A homogeneous structured CoCrNi medium-entropy alloy was synthesized by gas atomization and spark plasma sintering (SPS). The mechanical properties, corrosion resistance, and magnetic properties were reported in this study. The as-atomized CoCrNi MEA powder, with a spherical morphology in shape and a mean particle diameter of 61 µm, consisted of a single face-centered cubic (FCC) phase with homogeneous distributions of Co, Cr, and Ni elements. Also, the cross-sectional microstructure of powder particles gradually transformed from fully cellular structure into equiaxed-type structure with increasing particle size. After being sintered by SPS, the CoCrNi MEA consisted of a single FCC phase with a mean grain size of 20.8 µm. Meanwhile, the CoCrNi MEA can capable of offering an ultimate tensile strength of 799 MPa, yield strength of 352 MPa, elongation of 53.6%, and hardness of 195.3 HV. In addition, this MEA showed superior corrosion resistance to that of 304 SS (stainless steel) in both 0.5 mol/L HCl and 1 mol/L NaOH solutions. The magnetization loop indicated that this MEA has good soft magnetic properties.

Construction of visible light–responsive Z-scheme CdS/BiOI photocatalyst with enhanced photocatalytic CO2 reduction activity

Abstract: Rational construction of Z-scheme photocatalysts and exploration of the Z-scheme charge transfer mechanism have drawn much attention in the field of CO2 reduction because of its great potential to alleviate energy crisis and environmental problems. In this study, a series of Z-scheme CdS/BiOI composites were constructed by depositing CdS nanoparticles on the surface of BiOI nanosheets. The synthesized materials were characterized comprehensively, and their photoreduction CO2 activities were evaluated. The results show that the composites exhibit higher photoreduction CO2 activity under visible light irradiation (λ > 400 nm) than pure CdS and BiOI. The yields of CO and CH4 for the optimal composite after 3 h irradiation are 3.32 and 0.54 μmol/g, respectively. The improved photocatalytic activity is attributed to Z-scheme transfer mode of the photogenerated charges in the composites. The mechanism of CO2 reduction is proposed and verified experimentally.

Effects of titanium addition on microstructure and mechanical properties of CrFeNiTix (x = 0.2–0.6) compositionally complex alloys

Abstract: CrFeNiTix (x = 0.2, 0.3, 0.4, 0.5, and 0.6 molar ratio) compositionally complex alloys were fabricated by vacuum arc melting to investigate the microstructure, hardness, and compressive properties. The results revealed that CrFeNiTix alloys consisted of the principal face-centered cubic (FCC) phase and body-centered cubic (BCC) solid solution, with an amount of (Ni, Ti)-rich hexagonal close-packed phase. CrFeNiTix alloys exhibited the typical dendrite. Ti0.2 and Ti0.3 alloys were composed of FCC and BCC solid solutions in the dendrite, as well as e (Ni3Ti) and R (Ni2.67Ti1.33) phases in the inter-dendrite, simultaneously. For Ti0.4, Ti0.5, and Ti0.6 alloys, (Fe, Cr)-rich solid solution separated out and e phase transformed into R phase gradually. Meanwhile, TEM analysis indicated that Ti0.4 alloy matrix consisted of the principal FCC phase containing (Ni, Ti)-rich intragranular nanoprecipitates. The hardness values of CrFeNiTix alloys were increased with the addition of Ti content and the high compressive strength of CrFeNiTix alloys was maintained, which was attributed to the solid solution strengthening and precipitation hardening.

Hot deformation behavior of the high-entropy alloy CoCuFeMnNi

Abstract: In the present study, hot deformation behavior of a FCC high-entropy alloy CoCuFeMnNi has been investigated to explore the stress—strain response for a wide range of temperatures and strain rates. The deformation response has been examined by plotting a processing map and examining the evolution of microstructure and texture in each of the temperature—strain rate domain. Hot compression tests were carried out in the temperature range 850–1050 °C at strain rates varying from 0.001 s−1 to 10 s−1. Stress—strain curves indicate characteristic softening behavior due to dynamic recrystallization (DRX). DRX has been observed along grain boundaries, shear bands, as well as in the interior of deformed grains. The size of dynamically recrystallized grains shows a strong dependence on deformation temperature and increases with temperature. A high degree of twin formation takes place in the DRX grains evolved inside the shear bands, and the extent of twinning decreases at high temperatures. The optimal processing window has been estimated based on strain rate sensitivity and has been validated with detailed analyses of microstructure and texture. The best region for thermo-mechanical processing has been identified as in the temperature range 850–950 °C at strain rate 10−1 s−1.