Grain Density Research Articles

Obtaining Uniform High-Strength and Ductility of 2A12 Aluminum Alloy Cabin Components via Predeformation and Annular Channel Angular Extrusion

A 2A12 aluminum alloy component with uniform high-strength and ductility was developed via predeformation (one-pass repetitive upsetting extrusion) and annular channel angular extrusion (ACAE). Moreover, the microstructure evolution and age-hardening behavior were investigated. The results show that the upsetting-extrusion predeformation improved the cumulative strain of the component and refined the grain size, and that the second Al–Cu–Mg phases were obviously broken and refined, and that, especially, the distribution of the second phases along the extrusion direction was weakened. Thus, compared with directly ACAE-formed components, after the T6 heat treatment, the axial ultimate tensile strength (UTS) of the cabin increased from 476 to 484 MPa, and the elongation (EL) increased from 12.9% to 17.5%. The circumferential UTS increased from 426 to 482 MPa, and the EL increased from 9.24% to 16.8%. A large number of dislocations were introduced into the upsetting extrusion (UE) + ACAE method, which resulted in strain hardening and higher precipitation strengthening in the late artificial aging process. The finer and denser grains and s precipitates significantly enhanced the strength and ensured the good ductility of the alloy. It is suggested that the combination of predeformation and annular channel angular extrusion is an effective method for forming aluminum alloy cabin components with higher and more uniform mechanical properties.

Hot Compression Behavior of a Novel High Entropy Alloy

In this study, the flow behavior of a novel high entropy alloy, (FeNi)67Cr15Mn10Al5Ti3, was investigated through isothermal compression performed at temperature range of 980–1100 °C using strain rates of 0.01 s−1 and 0.1 s−1. The alloy was mainly composed of a face-centered cubic (FCC) phase and a small amount of body-centered cubic (BCC) phase. During deformation, the alloy exhibited typical single-peak type flow curve at all testing conditions. The stress exponent was determined to be ~5.5 with an apparent activation energy of ~426 kJ/mol, which indicated that dislocation creep was the rate-controlling process. Metallurgical inspection revealed that due to the plastic incompatibility of the two phases, the deformation is non-uniform especially at lower temperature and higher strain rate. Continuous dynamic recrystallization (CDRX) intensively occurred in both phases, but the recrystallization seemed to be much easier in the BCC phase. Dense low angle grain boundaries (LAGBs) were produced as a consequence of CDRX. At a lower strain rate, the LAGB ratio was evidently decreased with the increasing temperature. The sub-grain size was sensitive to the deformation parameter especially at a high temperature and low strain rate. A low temperature and high strain rate were beneficial for grain refinement but a much higher straining was required.

Cryogenic Mechanical Prelithiation Reduces Porosity and Improves Battery Performance of an Alloy Foil Anode.

Anode prelithiation could dramatically improve the initial Coulombic efficiency and battery life. Roll-to-roll mechanical prelithiation (MP) is an attractive option for achieving prelithiation in minutes. While our previous work on metallic-foil prelithiation revealed that an external pressure is necessary to achieve MP in a timely fashion, too high an applied pressure will cause severe damages in the form of porosity and cracking. Thus, gentler MP under smaller pressure, and surprisingly, cryogenic temperatures, while prepositioning prolific grain boundaries as lithium diffusion paths is critical. To this end, first, we developed an accumulative roll bonding (ARB) method to refine the grain size of Sn-5Sb foil for denser grain boundaries. After ARB of 12 cycles (ARB-12), the grain size of Sn-5Sb foil decreased from 20-50 to 0.5-1.5 μm. Then, MP was performed under a mild condition of 0.5 MPa and -20 °C. Thereby, the porosity of prelithiated ARB-12 was reduced to 1.8% from thickness measurement, significantly minimizing the prelithiation damage. As a result, due to grain refinement, we achieved lower interface impedance and better rate performance. The ARB-12 Sn-5Sb foil with a proper prelithiation design exhibited 180 and 110 stable cycles when pairing with commercial LFP and NCM811 cathodes. Furthermore, it also depletes less electrolyte and keeps higher capacity retention under -10 °C than that of the graphite anode.

Investigation of Electromechanical, Piezoelectric and Ferroelectric Properties of Ba(Zr0.05Ti0.95)O3 Ceramic

This paper demonstrates the structural, dielectric, ferroelectric, piezoelectric and electromechanical parameters of the pure-phase Ba(Zr0.05Ti0.95)O3 /BZT composition prepared through conventional solid state technique. The identification of compound and formation were analysed by X-ray diffraction (XRD) technique that demonstrated a pure perovskite phase of the synthesized composition. The sintering temperature- dependent density of the BZT ceramics wasstudied andthe sample with high density was considered for further study. Dense and well-defined grains were observed in the micrograph of the BZT sample studied by SEM analysis. The frequency depended dielectric study at the room temperature shows a very small variation of dielectric constant with frequency. Phase transitions related to orthorhombic symmetry to tetragonal symmetry, and, tetragonal symmetry to cubic symmetry were observed as of temperature variant dielectric study. The ferroelectric and piezoelectric strain behaviours were studied at different amplitudes and frequencies of applied field. The electromechanical parameters were obtained using the resonance and anti-resonance technique as mentioned in the IRE standard. The results obtained from the above studies point out that the BZT ceramic has the potential to be a candidate for environmentally friendly sensor and actuator device with high performance.

Microstructural evolution, dielectric performance, and densification behavior of novel NaAGeO4 (A = Sm, Y) ceramics

Novel NaAGeO4 (A = Sm, Y) ceramics with olivine structures were prepared and characterized. The phase composition, microstructural evolution, and densification behavior of the ceramics were investigated. The NaAGeO4 (A = Sm, Y) ceramics possessed a single orthorhombic crystal system with Pbn21 and Pnma space groups. The NaSmGeO4 ceramics had dense grains, clear boundaries, and low sintering temperatures, whereas a relatively wide range of sintering temperatures were feasible for the NaYGeO4 ceramics. The NaSmGeO4 ceramic material sintered at 1025 °C possessed excellent performance-related parameters, i.e., Q × f = 31,281 GHz, εr = 6.29, and τƒ = −48.3 ppm/°C, whereas those for the NaYGeO4 ceramic material were Q × f = 32,646 GHz, εr = 6.74, and τƒ = −39 ppm/°C at 1200 °C. Furthermore, doping the NaYGeO4 ceramic material with CaTiO3 to obtain 0.12CaTiO3-0.88NaYGeO4 yielded a τƒ value close to zero (−3 ppm/°C). The results demonstrate that NaAGeO4 (A = Sm, Y) ceramics have substantial potential for application in microwave devices.

A generalized model for dense axisymmetric grains flow with orientational diffusion

The flow of non-spherical grains is strongly affected by the orientation of the grains, as observed in experiments and simulations. An existing model that predicts the orientation of grains as a function of the flow field and shape of the grains, is limited to homogenous orientational fields where the interaction of the grains with their surroundings is negligible. To address this limitation, we generalized the model to account for inhomogeneous orientational fields in the form of spatial non-convective orientational flux. The orientational flux accounts for the interactions of grains with their surroundings and the boundaries. The proposed model is used to study the influence of orientational diffusion and boundary conditions on the flow of dense granular material down an incline. It is shown that the boundary conditions can play a significant role in the orientation of grains in such flows.

Photoconductive PbSe thin films and the role of potassium iodide

The PbSe thin films are sensitized by oxidation and iodization process to improve the infrared photoresponse enabling higher performing photodetectors and photovoltaic devices. Iodine is widely used for PbSe sensitization, and it influences the thin film morphology and also forms a PbI2 passivation layer. Potassium Iodide (KI) has been used as an additive in chemical bath deposited films of PbSe since 1959 and continues to this day. This work aims to better understand the role of KI in PbSe films as it improves MWIR photoresponse by as much as 300% compared to samples without KI. In this research paper, we show that low levels of KI (180 mMol) densify the PbSe film, increase grain size, reduce film stress/cracking, and improve IR absorption (proportional to dose). The transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies show thermal annealed PbSe films with KI convert round equiaxed grains to highly faceted grains coated with PbI2 ranging from 3 to 10 nm, throughout the film. The dense PbSe grains encapsulated in PbI2 lead to a more uniform PbSeO3 layer following thermal oxidation. The electrical resistance versus temperature measurements shows a strong phase transition occurs at 220 °C only for samples with KI. X-ray photoelectron spectroscopy studies confirm that PbSe films with KI annealed in an argon atmosphere at 460 °C have a surface layer of PbI2, and no potassium was detected, suggesting desorption or diffusion of potassium into the PbSe grains. PbSe films with KI showed 30x higher electrical resistance (RD) under dark conditions, leading to reduced carrier concentration (lower dark current) and improved photoresponse without impacting electron mobility. In summary, we have clarified the role of KI in PbSe thin films and how it can be used to improve the infrared photoresponse.

The intrinsic mobility of very dense grain flows

High mobility of natural disasters with severe consequences is often reported in large landslides and in earthquake fault ruptures. The mechanism of high mobility keeps to be mysterious to date. In this study, we used high-speed rotary shear experiments under normal stress 1 MPa and with a rotary speed of 2 m/s on grains of four different minerals to show that the tested dry dense grain flows with crushable grains are highly mobile intrinsically. Granular flow quickly weakens to a very low viscosity (about 500 Pa.s), which is independent of grain composition. We find that when flow begins, grains are crushed to a special fractal structure in which most larger grain is surrounded by much smaller grains. This special structure provides a favourable condition for generating and propagating acoustic energy from the abrasion indicated by the scratches on the grains. The scratching generates very high frequency elastic energy (vibration) in the larger grains, which profoundly weakens all grain contacts so that the grain mass flows like a giant flood. Chatter-marked scratches made by smaller grains scouring across boulders in rock-avalanche deposits suggest that the same processes occur in nature. This finding is important for the explanation of the behaviour of dense grain flows at large strains and high strain rates.

Wetting and corrosion properties of CuxOy films deposited by magnetron sputtering for maritime applications

Copper-based materials can be safe and economic alternatives for producing anti-biofouling coatings for large-scale applications. Although their antibiofouling properties have been previously described, the wetting and corrosion properties in specific environments such as the maritime industry has been far less explored.In this study, copper oxide (CuxOy) films were deposited by a DC reactive magnetron sputtering technique on stainless steel substrates. The oxygen amount during deposition was varied to obtain different structures. The films were characterised by SEM, EDS, XRD, AFM, and contact angle measurements. Oxygen incorporation into copper films promoted a significant change in the growth profile of the film, from dense and undefined grains to columnar grains with well-defined boundaries. Wettability results demonstrate that CuxOy films are high dispersive surfaces with poor affinity with seawater. Corrosion tests were performed in an NaCl (3.5% wt.) solution during 24 h through EIS and potentiodynamic polarization. The films were chemically characterized before and after corrosion tests by XPS as well as their ionic releasing process by ICP-OES spectroscopy. CuxOy coatings exhibited a poor corrosion resistance against artificial seawater and high ionic (Cu2+) release, which suggests a diffusion process. The results give insights into the chemical resistance of CuxOy films for application to avoid biofouling under seawater exposure.

Effect of Foliar Application of Micronutrients and Fungicides on the Nitrogen Use Efficiency in Winter Wheat

The increase in the grain density (GD) is the key factor for effectively controlling Nitrogen-Use Efficiency (NUE) in winter wheat. Winter-wheat protection with fungicides and/or foliar fertilization with micronutrients during the critical stages of yield formation affects the grain yield by increasing GD. This hypothesis was verified in a two-factor field experiment, carried out in the 2013/2014, 2014/2015, 2015/2016 growing seasons. A field experiment in a two-factor split-plot design, included three systems of wheat foliar protection (FP): (i) N + Mi (N + macronutrients), (ii) N + P (N + fungicides), (iii) N + Mi + P, and 0, 40, 80, 120, 160, 200, 240 kg N ha−1. The grain yield, despite the significant effect of years, depended on the interaction of FP and N doses. The maximum yield of 8.1, 10.7, 11.1 t ha−1 for the optimal N dose of 79.8, 227.4, and 245.2 kg ha−1, was achieved, respectively, for N + Mi, N + N, N + Mi + P. The wheat-grain yield depended significantly on GD (R2 = 0.98, p ≤ 0.001). Wheat protected with fungicides increased GD gradually with the N dose, reaching over 3000 grains per m2 when fertilized with 200 kg N ha−1. The lack of fungicide protection, reducing GD, consequently resulted in a greater accumulation of N in straw at the expense of grain. Fungicide protection of wheat through the positive effect on N management by wheat should be considered as an agronomic measure that supports N-Use Efficiency.

Enhancement of the piezoelectric property in PMN-PZT/PZT thin films

0.3Pb(Mg1/3Nb2/3)O3-0.7Pb(Zr0.52Ti0.48)O3/Pb(Zr0.52Ti0.48)O3 (PMN-PZT/PZT) piezoelectric films have been deposited on Pt/Ti/SiO2/Si substrates via in-situ magnetron sputtering process. The purpose of this work was to investigate heterogeneous interfaces-dependent preferential orientation, micro-morphology, and piezoelectric behaviors of the PMN-PZT/PZT films. Uniform and dense columnar grains are observed by Scanning electron microscope (SEM) analysis as increasing the number of hetero-interfaces. For the film with five heterogeneous interfaces (H5), the superior ferroelectricity (2Pr = 21.6 μC/cm2, 2Ec = 60 kV/cm) and dielectricity (εr = 1012.1, tanδ = 0.022 at 1 kHz) are obtained, which arises from highly dense columnar grain and the influence of heterogeneous interface strain. Moreover, an excellent piezoelectric constant e31 of 8.2C/m2 is achieved in H5 film, which is 3.5 times larger than that of PZT film. It is expected that this study will simulates the design and synthesis of new functional materials, and provides a guidance for actuators device fabrication and applications.

Structural, Morphological and Optical Properties of (Mn, Al) Co-Doped ZnO Thin Films Prepared by Sol-Gel Dip Coating Method

In this study, Aluminum (Al) and Manganese (Mn) co-doped ZnO thin films were successfully synthesized into glass substrates by the sol-gel dip-coating method with different Al concentrations (1%, 3%, and 5%). The structural, morphological, and optical properties of the obtained thin films were characterized by X-ray diffraction (XRD), Atomic force microscopy (AFM), and UV–VIS spectroscopy. XRD pattern revealed that the films have a polycrystalline hexagonal structure with a preferred orientation along (101) for undoped ZnO thin films, further the co-doped ZnO thin films show a shift in the preferred orientation to (002) direction without any Mn or Al related phases. The morphological analysis showed that the films have a uniform and dense ZnO grains, without any voids and cracks, and it was found that the surface roughness (RMS) increases from 8,27 to 14,43 nm when the Al doping concentration increased from 1% to 3%; however, when Al doping concentration is 5%, the RMS value decreased to 2,80 nm. From the optical analysis, the higher average transmittance was found to be corresponding to 5% Al doping concentration.

Effect of Magnesium Fertilization Systems on Grain Yield Formation by Winter Wheat (Triticum aestivum L.) during the Grain-Filling Period

The application of magnesium significantly affects the components of the wheat yield and the dry matter partitioning in the grain-filling period (GFP). This hypothesis was tested in 2013, 2014, and 2015. A two-factorial experiment with three rates of magnesium (0, 25, 50 kg ha−1) and four stages of Mg foliar fertilization (without, BBCH 30, 49/50, two-stage) was carried out. Plant material collected at BBCH: 58, 79, 89 was divided into leaves, stems, ears, chaff, and grain. The wheat yield increased by 0.5 and 0.7 t ha−1 in response to the soil and foliar Mg application. The interaction of both systems gave + 0.9 t ha−1. The Mg application affected the grain yield by increasing grain density (GD), wheat biomass at the onset of wheat flowering, durability of leaves in GFP, and share of remobilized dry matter (REQ) in the grain yield. The current photosynthesis accounted for 66% and the REQ for 34%. The soil-applied Mg increased the REQ share in the grain yield to over 50% in 2014 and 2015. The highest yield is possible, but provided a sufficiently high GD, and a balanced share of both assimilate sources in the grain yield during the maturation phase of wheat growth.

Characterization of Mo-6Ta alloy targets and its magnetron sputtering deposited thin film

In this study, pure Mo and Mo-6Ta alloy targets were produced by a manufacturing method, which is called die pressing with a combination of cold isostatic pressing and hot-pressing sintering technology, and molybdenum thin films were deposited on corning glass substrates using a DC magnetron sputtering system. The effect of alloying with tantalum on the phase structure, grain size, orientation, thin film surface morphologies and electrochemical properties has been investigated by a variety of techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) with electron back-scattered diffraction (EBSD), atomic force microscopy (AFM), four-probe resistivity tester, and electrochemical analyzer. The observation of the Mo targets reveals that this manufacturing technology with alloying of tantalum can reduce the target's grain size to lower than 50 μm with random grain orientation. The microstructure of the deposited Mo thin films indicates that the alloyed films have the higher deposition velocity with a dense fine grain structure and smoother surface. The sheet resistivity of the alloyed Mo film increases continuously with the increasing of the sputtering time, and eventually becomes higher than that of the pure Mo film. In electrochemical tests, both of the Mo films show capacitive reactance, and the capacitive arc radius of the alloyed Mo films are obviously larger than that of pure Mo films. The result of alloying with tantalum shows an increase in the corrosion potential of the Mo film from −0.5 V to −0.2 V, indicating improvement of the corrosion resistance of Mo films.

Pulsed laser deposited and sulfurized Cu2ZnSnS4 thin film for efficient solar cell

Kesterite quaternary material Cu2ZnSnS4, (CZTS)-based thin-film solar cells have attracted intensive attention owing to their earth-abundant nature, stable thermodynamic structure, and large potential for high power conversion efficiency (PCE) defined by their suitable optoelectronic properties. As a widely used thin film preparation method, pulsed laser deposition (PLD) has not been fully studied in CZTS thin-film solar cell. Herein, a promising route based on PLD from a quaternary target and post-sulphuration for CZTS thin film was achieved. Through systematical investigation and optimization of substrate temperature, laser pulse energy, and sulfurization temperature, the CZTS thin films showed single kesterite structure, high (112) orientation, and dense polycrystalline grains with controlled composition. The CZTS thin-film solar cell exhibited a record PCE of 6.62%, the highest reported value when using pulsed laser deposited and sulfurized process, due to its lower series resistance, reduced grain boundary effects, superior interface quality, and a suitable depletion width. This research offers a facile and robust preparation method for CZTS films with enhanced photovoltaic properties and increased efficiency.

Effect of laser surface cleaning of corroded 304L stainless steel on microstructure and mechanical properties

In this study, a high-power Nd:YAG laser is used to remove a corrosion layer on the surface of 304L stainless steel (SS304L). A laser power of 1140 W with different hatch distances and the number of repetitions is employed for corrosion removal. As shown by an electron probe X-ray microanalyzer, corrosion removal is successfully achieved via laser surface cleaning (LSC) with the small hatch distance or the large number of repetitions. However, corrosion residues remain at the surface of SS304L after the LSC process with the large hatch distance and the small number of repetitions. The effect of LSC process on the microstructure and mechanical properties of SS304L is investigated. The electron backscatter diffraction and transmission electron microscopy analyses reveal that the microstructure of SS304L depends significantly on the LSC conditions. In the LSC process with the large hatch distance and the small number of repetitions, only an increase in dislocation density is discovered. However, the LSC process with the small hatch distance or the large number of repetitions introduces dense dislocation structures, deformation twins, grain refinement, and precipitation. This microstructural alteration owing to the LSC process modifies the mechanical properties of SS304L in terms of hardness and tensile strength.

Effect of Reaction Time on the Synthesis and Sintering of Magnesium-Aluminium Spinel by Microwave Hydrothermal Synthesis

In this study, microwave hydrothermal synthesis of magnesium-aluminium spinel from pseudo-boehmite (AlOOH.nH2O) (n=0.62) and magnesium hydroxide (Mg(OH)2) for different reaction times is researched. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) are used to find out how the reaction time affects the synthesis of magnesium aluminium spinel precursors. The superficial properties of magnesium aluminium spinel precursors are investigated with scanning electron microscopy (SEM). According to XRD analysis, magnesium hydroxide reacts with pseudo-boehmite to form magnesium aluminium hydroxide hydrate. The median diameter of the samples obtained at 200 min was 5.958 μm. The agglomeration phenomenon was very serious especially when the synthesis time is greater than 200 min. The sintered sample obtained at 150°C for 200 min had more dense structure and smaller average grain size. The average grain size of the sintered sample was 0.527 μm. The best reaction time for microwave isothermal synthesis and sintering of magnesium aluminium spinel is 200 min.

Achieving high-performance n-type PbTe via synergistically optimizing effective mass and carrier concentration and suppressing lattice thermal conductivity

Introducing resonant levels is a potent strategy to improve the thermoelectric properties of the thermoelectric systems. However, the beneficial effect of resonant levels tends to be weakened with rising temperature for the PbTe system. This motivates us to introduce dynamic doping of Cu into Cr-doped n-type PbTe to achieve the fully optimized carrier transport over a wide temperature range. As a consequence, an extraordinary figure of merit, ZT of ∼ 0.55 at room temperature, a peak ZT of ∼ 1.31 at 773 K and an average ZT of ∼ 1.02 in the range of 323 to 823 K are obtained in the Pb0.975Cr0.025Te-0.2%Cu. Additionally, how co-doped of Cr and Cu contributes to suppressing thermal transports is still ambiguous. Herein, we employ comprehensive electron microscopy investigations to reveal that the synergistic incorporation of Cr and Cu into the PbTe matrix results in a series of phonon scattering sources, including massive point defects, high-density of nanoscale precipitates, microscale secondary phases, and dense grain boundaries, which can significantly reduce the lattice thermal conductivity by enhancing phonon scattering. This work clarifies the fundamental Cr-doping mechanism in PbTe and demonstrates that dynamic Cu-doping engineering is an effective approach to boosting thermoelectric performance, which should be applied in other thermoelectric materials.

Electrochemical study of a novel high-efficiency PbO2 anode based on a cerium-graphene oxide co-doping strategy: Electrodeposition mechanism, parameter optimization, and degradation pathways

A novel and efficient Ti/SnO2-Sb/PbO2-GO-Ce electrode was successfully fabricated based on the co-deposition of Ce ions and graphene oxide (GO) into β-PbO2 crystals and used as an anode for electrocatalytic oxidation of phenol. The electrodeposition mechanism, parameter optimization, mechanism analysis, and potential degradation pathways were discussed in depth. The co-doping of GO and Ce resulted in the high directional specificity of β(301), orderly and dense grain arrangement of PbO2 crystals. At the same time, the oxygen evolution potential, •OH generation capacity and lifetime were also improved. The effects of experimental parameters on phenol removal efficiency were evaluated, including the applied current density, electrode gap, supporting electrolyte, initial NaCl concentration, initial pH, and initial phenol concentration. Under the optimal conditions, the removal efficiency of phenol can reach 375.6 g m-2 h-1 for 20 min electrolysis, which is about 1.2 times that of the pure PbO2 electrode. The active oxygen species (•OH, ClO- and HClO) were important attributes to the degradation of phenol. Additionally, a potential degradation pathway for phenol was proposed. After 10 successive recycles, there was no significant difference of the electro-generated •OH, cell voltage and phenol removal rate, which confirms the stability and admirable reusability of Ti/SnO2-Sb/PbO2-GO-Ce electrode.

Intriguing triboelectrification behavior of identical P(VDF-TrFE) polymers

We report an intriguing triboelectrification behavior of thermally treated P(VDF-TrFE) polymers. Cooled (C-) and annealed (A-) P(VDF-TrFE) films were prepared by the rapid cooling of the melt solution and the subsequent annealing, respectively. The C–P(VDF-TrFE) had sparse grains and small elastic modulus and surface charge density, while, the A-P(VDF-TrFE) had dense grains and large elastic modulus and surface charge density. When the polymers contacted ITO electrodes, the triboelectric outputs of C-(PVDF-TrFE) were larger than those of A-P(VDF-TrFE). When the polymers contacted each other, the triboelectric outputs of different P(VDF-TrFE) films were significantly larger than those of similar P(VDF-TrFE) films. Based on detailed X-ray photoemission spectroscopy results, we suggested that roughness-induced frictional heat and elastic modulus differences may play an important role in minute material and/or ion transfer during the triboelectrification of identical P(VDF-TrFE) polymers.