Non-uniform Grain Research Articles

Multi-Class Grain Size Model for Forged Alloy 718 Aircraft Parts

The evolution of microstructural features such as local grain size and local grain size distribution are essential in view of the final physical and mechanical properties of the nickel base alloy 718 for aircraft parts forged in a multi-step production route. Due to increasing standards and the need of the prediction of fracture mechanical properties, a multi-class grain size model for a more detailed microstructure prediction is necessary. Therefore, a multi-class model considers the real initial non-uniform grain size distribution and structure of the pre-material at the beginning of the forging process, which affects the evolution of grain sizes during thermo-mechanical treatment and leads to different results than commonly used uniform grain structures. The initial distribution is defined by grain classes according the ASTM standard. It is shown that the presence of different classes and distributions of grains are as import as the applied strain, strain rate and temperature on dynamic, meta-dynamic and static recrystallization. Additionally, dissolution processes of delta phase and grain growth kinetics are included in the model to properly indicate the recrystallized fractions and represent the resulting multi-class microstructure. A series of simulations with different initial distributions is discussed and compared with examined forged samples in terms of the resulting microstructure for typical forging parameters. Based on these results the microstructure model can be used in combination with collected process data to predict the resulting properties and for the design of new aircraft parts.

Numerical simulation of atomization and combustion characteristics of high-moisture organic wastewater

The combustion method, due to its convenience and high-efficiency in harmless treatment, has been widely used in disposal of wastewater. With a wastewater burner as the study case, we performed numerical simulation by the Fluent software, analyzed the flowing and combustion process of the wastewater samples in the burner, compared the combustion effect of different atomization conditions — the spray cone model (hollow cone model, solid cone model), the spray angle, non-uniform grain size, uniform grain size. The study aims to provide suggestions for design and selection of wastewater burners.

The breakdown of Moore’s law induced by weak Anderson localization and by size effects in nano-scale metallic connectors

We report the resistivity measured at temperatures between 5 K and 300 K of a Cu film 63 nm thick with grains that have a diameter d = 10.5 nm on the average. The resistivity of this film is described by the first quantum theory of resistivity of nano-scale metallic connectors [R C Munoz et al, App. Phys. Rev. 4 (2017) 011102]. We also report an improved version of this theory that includes a new analytical description of the effect of grain boundary disorder on electron transport. We employ the surface roughness and grain size distribution measured on this Cu film as input data to compute, using our heory, the room temperature resistivity of Cu wires of rectangular cross section, and compare with the resistivity of these wires reported in the literature [M H Van der Veen et al, 2018 IEEE International Interconnect Technology Conference (IITC) (2018)], that are used for designing Integrated Circuits (IC) for the 14 nm, 10 nm, 7 nm, 5 nm, 3 nm and 2 nm nodes, respectively. The quantum theory predicts an increase in resistivity with diminishing wire dimensions that accurately agrees with the room temperature resistivity measured on these Cu wires. The resistivity induced by electron-rough surface scattering accounts for about half of the increase over the bulk observed in the 3 nm and 2 nm tech node; scattering by non-uniform grain boundaries contributes the remaining increase in resistivity—the latter is responsible for the weak Anderson localization. According to the description of electron motion furnished by this improved quantum theory, the break down of Moore’s law with shrinking wire dimensions is to be expected, since it originates from size effects triggered by electron scattering with rough surfaces and scattering by non-equally spaced grain boundaries, which become dominant as the dimensions of the metallic wire shrinks.

Structural, morphological and capacitive features of [(Pb0.5Bi0.25Y0.25) (Fe0.5Ti0.5)O3] solid state system

In the present assessment the Yttrium doped solid solution of BiFeO 3 and PbTiO 3 has been formed using solid state chemical itinerary. The structural, morphological and capacitive feature of single phase [(Pb 0.5 Bi 0.25 Y 0.25 ) (Fe 0.5 Ti 0.5 )O 3 ] solid state system has been detail studied to understand the capacitive properties. The primary study of XRD investigation affirms the solid state compound shows tetragonal structure. The non-uniform but non-void grains are spread on the surface of the material which is imitated from the SEM analysis. The substitution of small amount of Yttrium to BFO-PT solution enhances the dielectric constant as well as reduces the tangent loss or electrical leakage which is studied from temperature and frequency response of corresponding electrical parameter of the material. Due to the above important characteristics the promising material may be stand as a contender for development of different electronic perceiving device.

ELECTROCHEMICAL SENSING OF H2O2 BY HYDROTHERMALLY SYNTHESIZED PURE COPPER OXIDE MATERIALS

We report the variations in structural and morphological properties of hydrothermally synthesized pure CuO materials,prepared by employing three different stochiometric concentrations of reagents (details given in experimental section), followed by autoclaving at different temperatures e. g. 160oC and 180oC for 6 hours. X-ray diffraction (XRD) revealed the presence of single (monoclinic: CuO) and mixed (monoclinic as well as cubic Cu2O) phases of copper oxide and cupric oxide respectively. Scanning Electron Microscopy (SEM) images reveal irregular distribution of particles having non-uniform grain shapes of all prepared materials except for the one having pure monoclinic structure. Most of the materials had comparable morphologies whereby sharp edges and flat surfaces of particle were observed. The particle size was ranging between 2µm to 4µm. One of the samples (having pure monoclinic structure) was further characterized for dc-electrical conductivity followed by electrochemical detection of H2O2. Results show appreciable ability of the material towards H2O2detection for concentrations as low as 2mM.

Imaging the Surface of a Polycrystalline Electrodeposited Cu Film in Real Time Using In Situ High-Speed AFM

We studied the surface evolution of polycrystalline Cu films electrodeposited from an organic additive-free acid sulphate electrolyte on to a gold microelectrode using a high-speed Atomic Force Microscope (HS-AFM) which images an area of 2 × 2 μm at 2 frames per second and a resolution of 1000 × 1000 pixels. The ability to acquire data at this rate opens even fast growth processes to in situ investigation. Real-time images from a film deposited at ∼0.5 nm s−1 revealed many interesting phenomena, most significantly highly non-uniform grain growth rates with several examples of grains showing accelerated growth compared to their neighbours. Grain overgrowth was also observed in different regions of the sample. Surface roughness scaling and slope analysis provided evidence for structural coarsening of the film and an increase in the mean slope θ with increasing film thickness t. We show how both grain overgrowth and an increase in θ can contribute to the coarsening of the surface structure as deposition proceeds.

Solid rocket motor propellant grain burnback simulation based on fast minimum distance function calculation and improved marching tetrahedron method

To efficiently compute arbitrary propellant grain evolution of the burning surface with uniform and non-uniform burning rate for solid rocket motor, a unified framework of burning surface regression simulation has been developed based on minimum distance function. In order to speed up the computation of the mini-mum distance between grid nodes of grain and the triangular mesh of burning surface, a fast distance querying method based on the equal size cube voxel structure was employed. An improved marching tetrahedron method based on piecewise linear approximation was carried out on second-order tetrahedral elements, achieved high-efficiency and adequate accuracy of burning surface extraction simultaneously. The cases of star grain, finocyl grain, and non-uniform tube grain were studied to verify the proposed method. The observed result indicates that the grain burnback computation method could realize the accurate simulation on unstructured tetrahedral mesh with a desirable performance on computational time.

Detailed analysis of structural and optical properties of spinel cobalt doped magnesium zinc ferrites under different substitutions

Spinel ferrites nanoparticles have complex considerable interest in several technical applications because of their different magnetic behavior. These magnetic nanoparticles obtain finite size and surface effects. The Co doped Mg-Zn ferrites were prepared by co-precipitation method. The structural characterization of the samples was done for Mg0.5Zn0.5-xCoxFe2O4 (X = 0.01–0.05) nano ferrites using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV spectroscopy and Fourier transform infrared spectroscopy (FTIR). The cubical spinel structure of single phase has been obtained. As the concentration of Cobalt in the magnesium zinc ferrite increases, the crystallinity of the cubic spinel phase gradually increases. As increasing the concentration of Co+2 the lattice constant disorderly the lattice symmetry. Absorption spectra display a change in position of maximum absorption near the higher wavelength with increased Co2+ content. Some XRD parameters, using proposed X-ray morphology index, average crystalline size, lattice parameter, Density, Volume of unit cell, etc., have been evaluated. The absorption spectra reveal that in visible region Co-doped Mg-Zn ferrite close infrared region has low absorption rate moreover; in UV region the absorption is high. The evaluation of bandgap of Co-doped MgZnFe2O4 is the important features of its optical characteristics. The SEM image shows the non-uniform grains distributions for all compositions. The IR spectroscopy is a versatile tool for the identification of purity, functional groups, and phase of samples.

Hardening behavior and deformation microstructure beneath indentation in heavy ion irradiated 12Cr-ODS steel at elevated temperature

Hardness behavior and deformation of the microstructure beneath the indentation in 12Cr-ODS steel after exposure to heavy ion irradiation at 573 K were investigated with combined applications of nano-indentation tests, EBSD analysis, and TEM observation. The inhomogeneous nano-indentation hardness behavior was firstly investigated in both non-irradiated and irradiated specimens and compared to those at room temperature (RT) irradiation. Subsequently, TEM observations were performed to understand the deformation behaviors beneath the indentation tested at typical low-indexed orientations. Obvious irradiation hardening was confirmed in both the normal direction (ND) and rolling direction (RD) specimens, and the hardening effect intensified with an increase in irradiation dose. Meanwhile, various anisotropic hardness behaviors were observed such as a lower hardness value and a weaker hardening effect in the RD specimen compared to the ND specimen, and a lower hardness value but a greater hardening effect in [001] orientation relative to [111] orientation. Furthermore, results from 573 K irradiation showed similar anisotropic hardness behaviors with those obtained from RT irradiation, despite the fact that irradiation at 573 K exhibited a weakened irradiation hardening effect in this steel. TEM observation of the deformation microstructure beneath the indentation reveals that (i) the depth of the deformation affected zone varied with orientation, ranging from ~6-9 times that of the indent depth, and (ii) distinct dislocation-grain boundary (GB) interactions beneath the indentations was confirmed to exhibit dependence on the geometric relation between GB and indenter impression direction. Correlation between the anisotropic hardness behavior and microstructural features is discussed based on Schmid factor analysis, comparison of geometric favorability between indenter and possible slip planes, and TEM observation of deformation microstructure. The results conclude that the anisotropic hardness behaviors in the present 12Cr-ODS steel are ascribed to the combined effect of crystal orientation and the non-uniform grain morphology with the existence of the elongated grains having low aspect ratio in the ND plane and nano-layered grains in the RD plane.

An experimental and theoretical insights into the dielectric properties of (Li, Nd) co-doped ZnO ceramics

In this work, we report the combined effect of donor (Nd) and acceptor (Li) co-doping at the Zn site of ZnO ceramics on structural, microstructural, and dielectric properties. Combining experimental observations with DFT-based theoretical study, we have shown that before experimental fabrication DFT-based first principles study can be used as a good indication to have prior qualitative assessment of a dielectric medium. For implementing this objective, various Li and Nd co-doped ZnO ceramics have been synthesized through the conventional solid-state reaction route. Quantitative XRD analysis reveals the formation of wurtzite hexagonal structured ZnO having space group P63mc. Meanwhile, FESEM micrographs confirm the formation of randomly aligned non-uniform grains in size and shape. We show that the average grain size distribution and density of the studied compositions are two tuning factors to control the dielectric properties of these compounds. Though the value of dielectric constant is decreased with the increase in doping content, the optimum composition Nd0.005Li0.005Zn0.99O exhibits slightly lower dielectric constant ( $$\approx$$ 2066 at 1 kHz) than pristine ZnO but relatively very low dielectric loss ( $$\approx$$ 0.20 at 1 kHz) at room temperature than pure ZnO ceramics sintered at 1623 K. For understanding the dielectric relaxation mechanism in the studied ceramics, complex impedance spectra analysis has also been performed and discussed thoroughly. This study provides a new insight for further development of ceramic materials with improved dielectric properties.

Influence of Ba2+ Doping on Structural and Electrical Transport Properties of YMnO3 Ceramics

The pristine and barium (Ba2+) doped YMnO3 (Y1−xBaxMnO3; x = 0.00 and 0.05) ceramic samples were synthesized through the solid-state reaction method. The X-ray diffraction, Raman spectroscopy, and scanning electron microscopy were performed for the structural and morphological studies. The electrical transport properties were investigated using dielectric and modulus spectroscopy. The XRD patterns of the titled ceramics have shown the monophasic hexagonal structure having P63cm space group symmetry. The average crystallite size is found to decrease on partial substitution of Ba2+ cation. Raman spectroscopy was performed to observe the local disorder and variation in the modes with the introduction of dopant in the pristine ceramic. The surface morphology displays the formation of non-uniform grains in the ceramics. The dielectric spectroscopy reveals a decreasing trend in both the dielectric constant and dissipation factor with increasing frequency. It indicates the significant role played by the space charge polarization. The electrical modulus study of the ceramics was also performed to explore the electrical transport phenomenon. The present study reports the enhanced dielectric nature of doped materials.

Structure instability and high microwave dielectric permittivity of nonstoichiometric (Sr0.4Ce0.4)1-xNdxTi0.8Mg0.2O3 system for wireless communication

(Sr0.4Ce0.4)1-xNdxTi0.8Mg0.2O3 [(SC)NdTMgO3, x = 0.1–0.4] non-stoichiometric system were obtained through conventional solid-state synthesis technique. All perovskite peaks were attributed to either single (x ≤ 0.3) and/or mixed (x = 0.4) like phases. A solid solution of cubic structure was obtained for x ≤ 0.2, however, for x ≥ 0.3, the (SC)NdTMgO3 compound, exhibits structure instability and (200)/(310) peaks splitting. The peaks splitting indicates cubic (C-phase) to tetrogonal (T-phase) structure phase transition. All ceramic samples appear nearly dense, presenting a non-uniform grain size distribution. The observed trend of the microwave dielectric properties (εr, τf, Q × f) is mainly related to the formation of structure phase transition, packing fraction, relative density and ionic polarizability. A key microwave (MW) dielectric properties of εr = 53, Q × f = 26,700 GHz and τf = +2.8 pmm/°C could be obtained for composition with x = 0.4.

Investigation on Mechanical Behavior of Friction Stir Welded Nylon-6 Using Temperature Signatures

The present investigation focused on parametric optimization for improving joint efficiency of friction stir welded nylon-6 sheets using particle swarm optimization algorithm using a response surface method-based regression model. Initially, parametric effects on weld quality characteristics such as weld bead profile, bead shape and its microstructure along with micro-hardness variation and stress–elongation behavior of the butt weld have been studied considering cylindrical, square and triangular pin contours. The thermal cycles along advancing and retreating side of tool rotation have also been acquired during welding which was further used in the response surface models for the improvement in weld quality prediction capability. The joint efficiency was found to be maximum (49.68%) at intermediate value of each parameter using square pin. The material scooping action and undercut defects along with non-uniform grain morphology with micro-cavities were primary reasons for weld failure at weld interface. The response surface-based regression model of joint strength of the weld was significant, whereas weld hardness and percent elongation were found to be insignificant. However, weld peak temperature with associated cooling rate-based regression models was found to be highly adequate as per substantial improvement for the prediction of each weld quality-based features. Finally, response surface-based regression model of joint strength was further used for parametric optimization using response surface method as well as evolutionary particle swarm optimization tools. The particle swarm optimization was found to be more precise with better optimization capability than response surface methodology.

Structural, optical, dielectric, and multiferroic properties of sodium and nickel co-substituted barium titanate ceramics

Narrowing the bandgap energy of perovskite ferroelectrics is a potential task for improving PV applications. This study examined the effect of Ni2+/Na+ co-substitution on the structural, optical, electrical, and magnetic properties of Ba1-x(Nix/2,Nax)TiO3 (BTNaNi-x) ceramics, where (0 ≤ x ≤ 0.08), prepared by solid-state reaction method. X-ray diffraction along with structure refinement verifies the existence of perovskite structure with a tetragonal phase in all samples. The morphological study reveals a non-uniform grain size distribution with a decrease in grain size with an increase in co-substitution concentration. XPS study gives direct evidence of oxygen vacancies in the investigated sample. The oxygen vacancies and octahedral distortion accompanying the Ni2+/Na+ co-substitution significantly reduce the optical bandgap of BaTiO3 ceramics from 3.14 to 2.688 eV. The temperature dependence of the dielectric constant is measured in the range of 30–250 °C at the frequency of 1 kHz. The results reveal that the transition temperature gradually decreased with an increase in Ni2+ and Na+ concentrations. This phenomenon was interpreted based on reducing grain size and tetragonality with co-substitution. The ferroelectric and magnetic properties are determined by (P–E) and (M–H) hysteresis loops at room temperature. Magnetic properties are significantly enhanced with an increase in the Ni2+, Na+ contents in the system. The correlation between the ESR width parameter (ΔH) and asymmetry parameter (Pays) with concentrations (x) reveals that the sample with x = 0.08 has a strong magnetic nature compared to other samples.

Improving the yield strength of an antibacterial 304Cu austenitic stainless steel by the reversion treatment

As an implant material, Cu-bearing austenitic stainless steels can possess the antibacterial property, but their mechanical strength is low. In order to improve the yield strength of a 304Cu (17%Cr–7%Ni–3%Cu) alloy through substantial grain refinement, a research investigation has been taken up to conduct the reversion annealing treatment comprising a heavy (71%) cold rolling reduction followed by annealing at various temperatures (650–950 °C) and durations (1–5400 s). The microstructure evolution was examined by electron backscatter diffraction and further characterized by magnetic measurements, and mechanical properties were determined by tensile and hardness testing. The precipitation of Cu was confirmed by transmission electron microscopy. It was found that the reversion of deformation-induced martensite to austenite took place by the shear mechanism, followed by subgrain formation and continuous recrystallization resulting in quite non-uniform grain size distribution. The finest reversed grains were around 0.6 μm in size, but also much larger austenite grains and a small fraction of unreversed martensite existed in the final structure despite annealing at least up to 800 °C. Coherent Cu particles were observed after aging for 1.5 h at 700 and 650 °C, while the yield strength could be improved to 507 and 791 MPa, respectively, i.e. by ~2–3 times that of the annealed steel. The ductility of the steel remains still high, the fracture elongation being 36%.

An impedance spectroscopy study of sol-gel prepared La0.9Sr0.1Fe0.7Mo0.3O3 perovskite

In this present work, impedance spectroscopy was applied to investigate the electrical properties of La0.9Sr0.1Fe0.7Mo0.3O3 (LSFMo) perovskite prepared by sol-gel and sintering methods. SEM analysis reveals the non-uniform grain distributed in samples with average grain size 347 nm. The complex impedance has been examined in the frequency range of 100 Hz–1 MHz and temperature range of 75–250 °C. The Nyquist plots were identified to form single semicircular arc described as grain behavior working in conduction mechanism. The dielectric and complex conductivity is shown depending on the temperature and frequency. The evolution of ln σDC vs 103/T (K−1) satisfies Arrhenius law and the activation energy is found to be 0.45 eV for this conduction mechanism.

Effect of Grain Structure on the Mechanical and Corrosion Behavior of Advanced Medium Mn Stainless TWIP Steel

The influence of recrystallization annealing on the microstructure, mechanical properties and corrosion behaviour of an austenitic TWIP steel bearing medium Mn and V alloying was investigated. The steel undergone a heavy cold deformation of 65 % reduction. Subsequently, recrystallization annealing at 1000 °C and 1100 °C for 15 min was conducted to achieve different grain structures. The microstructural evolution was studied using optical microscopy and electron backscatter diffraction technique. Mechanical properties were determined using tensile tests at room temperature. Corrosion behaviour was measured by cyclic potentiodynamic polarization at 3.5 pct NaCl. For comparison, austenitic stainless-steel Type 201 was used in this study. It was observed that at 1000 °C, a non-uniform austenitic grain structure with vanadium carbides distributed throughout the matrix was obtained. However, a coarse grain structure without carbides was induced at 1100 °C. The fine-grained structure enhanced at 1000 °C exhibited higher strength and good ductility. Contrary to this, the corrosion results showed that a significant deterioration in the corrosion resistance could be observed in sodium chloride solution for the achieved structure at 1000 °C compared to 201 stainless steel.

Enhanced magneto-capacitance in Sr2+ modified BiFeO3–PbTiO3 solid solutions

Polycrystalline ceramics of 0.7BiFeO3-0.3 Pb(1-x)SrxTiO3 compositions with x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0 were successfully synthesized by solid state reaction method. The structural, microstructural, ferroelectric, magnetic, dielectric and magnetocapacitive properties have been investigated. X-Ray diffraction analysis using Rietveld refinement revealed the existence of multiphase region with rhombohedral (R3c) and tetragonal (P4mm) polymorphs for x = 0, 0.2, 0.4, 0.6 & 0.8 and single phase with cubic crystallinity for x = 1.0 with Pm3‾m space group. SEM micrographs depicted dense microstructure with non-uniform grains. Except x = 0, pinched ferroelectric loops have been observed for x = 0.2, 0.4, 0.6, 0.8 and 1.0 with low remnant polarization. Sr2+ substitution enhanced the magnetization by suppressing antiferromagnetic spin cycloid of BiFeO3 and the maximum value of remnant was found to be 9.98 memu/g for x = 1.0. Room temperature dielectric studies revealed that the dielectric constant decreases with increasing Sr2+ content in the composition. The magnetoelectric coupling was measured through observing the relative change in dielectric constant induced by applied magnetic field (Magnetocapacitance: MC). The maximum value of magnetocapacitance was found to be 0.88% for the composition with x = 0.6. The magnetic field induced fractional dielectric constant can also be expressed as MC ~ γM2 using Ginzburg–Landau theory and the linear fitting gave the value of positive value of magnetoelectric interaction constant, γ = 3.79, 2.08 and 1.76 for x = 0, 0.06 and 1.0, respectively.

Single-Shot Compressed Photoacoustic Tomographic Imaging with a Single Detector in a Scattering Medium

Photon scattering imposes a fundamental restriction on optical imaging in turbid media. In this work, we propose a compressive-sensing-based photoacoustic imaging modality that allows single-shot tomography with a single detector in a scattering medium. The nonuniform optical speckle grains created in the diffusive regime, which act as a conventional drawback of optical modality, are used to generate ultrasound locally. The photoacoustic signals from spatial positions can be well extracted from a superimposed signal via introduction of locally modulated time delays. Taking advantage of the compressed measurement assisted by the acoustic mask, we demonstrate a theoretical compressed framework of three-dimensional photoacoustic surface tomography with a broad field of view after one-time optical illumination. This approach can increase the photoacoustic imaging efficiency greatly and reveals the potential for dynamic imaging in optically diffusive media.

Thickness dependent structural, electrical and optical properties of cubic SnS thin films

This paper reports the thickness dependent structural, optical and electrical properties of tin monosulfide (SnS) films. SnS films of different thickness were grown (at 24 °C) by chemical bath deposition. Films of different thicknesses were obtained by varying the number of deposition cycles (2, 3, 4, 5 and 6 cycles; one cycle = 4.25 h). All films were examined by employing different experimental techniques. XRD results showed the occurrence of cubic π-phase in all films. FTIR spectra confirmed the occurrence of main peaks corresponding to Sn–S bond stretching in all films. Atomic force microscopy (AFM) analysis of all films showed non-uniform grain distribution with porous surface morphology. Surface roughness was found to increase (32 ± 1 nm to 72 ± 1 nm) with increase in film thickness. Optical measurements showed that the films exhibited direct energy band gap, Eg. The Eg was found to increase from 1.70 eV to 1.74 eV with increase (374 ± 5 nm to 723 ± 8 nm) in film thickness. All films exhibited high absorption coefficient α (≥104 cm−1) in the visible region. Film with lower thickness (374 nm) exhibited higher absorption coefficient. Electrical measurement of the films revealed that the electrical resistivity ρ had strong dependence on film thickness. The electrical resistivity ρ was found to increase (1.592 × 103 Ω cm to 1.785 × 104 Ω cm) with increase in film thickness. All results suggested that the optical response and electrical conductivity could be tuned through appropriate choice of film thickness by maintaining the cubic structure.