Platelet-like Grains Research Articles

Influence of Ti3AlC2 additions on CMAS corrosion resistance of porous LaMgAl11O19 abradables

The corrosion of calcium-magnesium-aluminosilicate (CMAS) is a critical degradation mechanism for the hot sections of aircraft engines, particularly affecting abradable components where inherent defects complicate the prevention of rapid CMAS melt penetration. To address this challenge, Ti3AlC2 was incorporated into the porous LaMgAl11O19 abradables at concentrations of 5–20 wt% as both a self-healing agent and sintering aid. Annealing at 1200 °C markedly improved crack closure and pore isolation within the coating, with these effects intensifying with higher Ti3AlC2 concentrations, and resulted in the retention of excess TiO2. CMAS interaction tests conducted at 1300 °C demonstrated that only the abradables with 20 wt% Ti3AlC2 addition significantly reduced the penetration of CMAS melt. This effect is attributed to the densification of the abradables caused by self-healing, which blocks the propagation of CMAS along defect channels, and the role of TiO2 as a nucleating agent that facilitates the crystallization of CMAS and the precipitation of CaAl2Si2O8. The La/Ca ratio in the solid solutions related to LaMgAl11O19 and LaTi2Al9O19 can be used to reflect the corrosion level of platelet-like grains, where a value below 1 is likely to trigger their dissolution.

Ferroelectric domain structure in Bi4Ti3O12 ceramics: Insights from Confocal Raman Microscopy

Bismuth Layer-Structured Ferroelectric (BLSF) materials with Bi4Ti3O12 composition exhibit high ferroelectricity, potential for high-temperature piezoelectricity, and the puzzle of low polarizability, explored via textured ceramics and domain configurations. Here, we show that a distinctive stripe configuration of 90° domains emerges for large platelet-like grains, while the smallest grains, possessing a more equiaxial morphology, exhibit a needle-like domain structure that significantly impacts the ferroelectric properties of the ceramics. The observed hysteresis loops suggest that polarization is effectively clamped, owing to reduced mobility along the needle-like domain walls, thereby leading to a reduction in remnant polarization as grain size diminishes. It is elucidated that the domain structure is intricately linked to both internal stress within the grains and the presence of defects, notably oxygen vacancies, at the domain walls. Consequently, these multifaceted factors are identified as key determinants of the ferroelectric activity within ceramics bearing such a distinctive crystalline structure.

Rare-earth high-entropy magnetoplumbite structure hexaluminates (La1/5Nd1/5Sm1/5Eu1/5Gd1/5)MAl11O19 (M = Mg, Zn) for thermal barrier coating applications with enhanced mechanical and thermal properties

By applying the high-entropy strategy, one can develop stable mixed oxide by populating a single sublattice with many distinct cations. Two kinds of rare-earth high-entropy hexaaluminates (La1/5Nd1/5Sm1/5Eu1/5Gd1/5)MAl11O19 (M = Mg and Zn) were successfully synthesized, and their mechanical and thermal properties were analyzed. We highlight that the Zn-containing sample displays a significant increase in fracture toughness (2.48 MPa m1/2) and a decrease in thermal conductivity (1500 °C, 1.2 W m−1 K−1) as compared to the Mg-containing sample. The diffusion of fine grains in platelet-like grains observed only in the Zn-containing sample is considered to be responsible for its outstanding mechanical properties. This work demonstrates the excellent thermal-mechanical properties of the Zn-containing sample and indicates the promising use of high-entropy hexaaluminate in the aerospace field acting as thermal barrier coating materials.

Synthesis of M-type hexaferrite reinforced graphene oxide composites for electromagnetic interference shielding

This study focused on addressing the increasing demand for materials that can effectively shield against electromagnetic interference. In particular, Ba0.7Mn0.3Nd0.1Fe11.9O19 M-type hexaferrite was synthesized using the sol–gel auto-combustion method and sintered at 1050 °C. The modified Hummer process was used to prepare graphene oxide (GO), and three composites were then synthesized with the ultrasonication method, which were denoted as C-1 (90 % M-ferrite + 10 % GO), C-2 (80 % M-ferrite + 20 % GO), and C-3 (70 % M-ferrite + 30 % GO). X-ray diffraction (XRD) analysis confirmed the formation of the hexagonal phase of the M-type barium hexaferrite and GO. A prominent peak at an angle of 8.82° corresponding to the (001) reflection was observed by XRD analysis for the GO sample and it confirmed the effective oxidation of graphite and formation of GO. Scanning electron micrographs of M-type hexaferrite demonstrated the formation of platelet-like grains with hexagonal shapes, which were suitable for microwave absorption. The direct current electrical resistivity at room temperature was determined as 2.08 × 10−8 Ω-cm for the M-type ferrite, and the resistivity of the composites decreased as the concentration of GO increased due to the superior conductivity of GO compared with the ferrite. The dielectric properties of all samples followed the Maxwell–Wagner model. The dielectric characteristics increased in magnitude as the GO content increased. The AC magnetic susceptibility decreased for the M-type ferrite and three composites as the temperature increased to eventually reach a steady state at a specific temperature known as the Curie temperature. Except for GO, the Curie temperatures of all samples were within the range of 348 K–450 K. Coupling magnetic ferrite with GO allows the magneto-electrical characteristics to be tuned, with possible uses in electronic devices, electromagnetic shielding, supercapacitors, and water purification.

Evolution of Nd-rich phase distribution in Hot-Deformed Nd-Fe-B magnets with different height reductions

In this study, the Nd-rich phases evolution of hot-deformed (HDed) Nd-Fe-B magnets with different height reductions was systematically studied. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results showed that, disorderly oriented platelet-like grains were generated in the hot-pressed magnets subjected to a high-temperature treatment without any deformation. In this case, the grain boundaries (GBs) and triple junction regions (TJRs) provided abundant space for storing Nd-rich phases inside the ribbons. With the height reduction, the platelet-like grains continuously grew and were regularly arranged, resulting in a decrease in GBs and TJRs inside the ribbons. owing to the lack of storage sites, liquid Nd-rich phases can be easily squeezed into the gaps between the ribbons to form blocky Nd-rich phases under pressure. The energy-dispersive X-ray spectroscopy (STEM-EDS) results indicated that the formation of blocky Nd-rich phases not only led to formation of the thin grain boundaries but also resulted in a decrease in the non-ferromagnetic phase element content inside the ribbons. owing to the weakened pinning effect of the GBs on the domain walls, the mechanism of coercivity gradually changed from pinning field control to magnetic domain reversion nucleation. Consequently, with the height decreased by 70%, the remanence increased from 8.32 kGs to 13.62 kGs, while the coercivity significantly decreased from 19.62 kOe to 11.57 kOe. Therefore, it is crucial to avoid the formation of blocky Nd-rich phases for fabricating HDed Nd-Fe-B magnets with high coercivity.

Improved coercivity of W- and M-type composite hexaferrites using two different synthesis routes

Two series of W- and M-type composite hexaferrites were synthetized using the conventional ceramic method in two different synthesis routes. In the first synthesis route, W- and M-type composite hexaferrites were formed by reaction in the pre-sintering stage. In the second synthesis route, W- and M-type composite hexaferrites were obtained by physically mixing W- and M-type hexaferrites in the second ball milling stage. The influence of M-type phase on the structure and magnetic properties of W-type hexaferrites synthesized in both synthesis routes are investigated in detail. For both synthesis routes, X-ray diffraction (XRD) patterns of all samples indicated crystallization of W- and M-type hexaferrites phase and scanning electron microscopy (SEM) measurements revealed hexagonal platelet-like grains. In the pre-sintering stage, the saturation magnetization (4πMs) of all samples ranged between 3.30 kG and 4.25 kG. The remanence ratio (Mr/Ms) changed from 0.77 to 0.88 with the increase of pre-sintering temperature. The coercivity (Hc) of all samples ranged between 456 Oe and 1846 Oe. The ferromagnetic resonance (FMR) linewidth (ΔH) ranged between 466 Oe and 748 Oe. In the second ball milling stage, 4πMs and Mr/Ms maintained a relatively stable value of ~4.5 kG and ~0.89, respectively. Hc increased from 519 Oe to 620 Oe with the increase of M-type hexaferrites. ΔH ranged between 317 Oe and 573 Oe. We note that in both synthesis routes only the composite hexaferrites synthesized in the pre-sintering stage have a significantly improved coercivity from 456 Oe to 1846 Oe. This enhancement in coercivity is attributed mainly to the effect of exchange coupling among ferrite grains. In addition, the ΔH decreases with the addition of M-type hexaferrites.

Magnetron Sputtered Perpendicular Barium Hexaferrite Thin Films Produced by the Multilayered Method

We report on the synthesis and characterization of thin M-type barium hexaferrite (BaFe12O19 or BaM) films on sapphire (0001) substrates by RF magnetron sputtering. Single layers of 150 nm, 200 nm (S200), 400 nm (S400), 600 nm, and 700 nm were fabricated. Multilayered technique with inner-layer annealing was employed to fabricate the 400 nm (M400) BaM films. The thickness dependence of the magnetic, structural, elemental analysis, and surface morphological properties of the BaM films has been investigated using VSM, XRD, EDX, and SEM, respectively. For the M400 BaM films, excellent magnetic properties with high values of out-of-plane coercivity (Hc┴ = 3.1 KOe) and squareness (S┴ = 0.9) were obtained. The surface morphology of the M400 shows a platelet-like grains, which have their c-axis orientation in the out-of-plane direction. The magnetic properties and XRD data of the S200 films and M400 were about the same. For the single S400, S600, and S700 films, the magnetic properties have been reduced due to the excess oxygen concentration and the exchange interactions, the stress relaxation of the lattice constant, and the formation of the acicular grains. The acicular grains of the S400 films favor their c-axis aligned in the in-plane direction.

Preparation and properties of hot-deformed magnets processed from nanocrystalline/amorphous Nd–Fe–B powders

The hot-deformed magnets processed from nanocrystalline/amorphous Nd–Fe–B powders were prepared under different hot-pressing temperatures (600–750 °C, at intervals of 25 °C) by the self-made hot-pressing equipment. The microstructure and magnetic properties of hot-deformed magnets prepared at different temperatures were also investigated. When the temperature is above 650 °C, the density of magnet reaches 7.5 g·cm−3. The optimum magnetic properties of magnetic induction intensity of Br = 1.3 T, optimum energy product of (BH)max = 282.5 kJ·m−3, intrinsic coercivity of Hcj = 1130.0 kA·m−1 of hot-deformed magnets are obtained at hot-pressing temperature of 650 °C. X-ray diffractometer pattern shows that the (00L) texture has been obtained. For the microstructural characteristic, on the one hand, the good magnetic performance is attributed to the fine platelet-like grains with an average length of 410–440 nm at the hot-pressing temperature range from 625 to 675 °C. On the other hand, the unaligned coarse grains are observed in all the samples. And the areal fraction of those is gradually increasing with the rise of the hot-pressing temperature, which tends to deteriorate the magnetic properties. The composition map shows the accumulation of Nd/Pr-rich phase in the coarse grains’ region.

Structural, magnetic and Mössbauer analysis of lanthanum and nickel doped Co2Y-type hexaferrite nanomaterial matrix synthesized by sol-gel auto-combustion technique

Sol-gel auto-combustion technique was used to prepare the lanthanum (La3+) and nickel (Ni2+) doped Co2Y-type Sr2-yLayCo2NixFe12-xO22; x = 0.0, 0.1, 0.2, 0.3; y = 0.0, 0.01, 0.02, 0.03 nanohexaferrites materials. Synthesized nanohexaferrites were characterized by XRD, FTIR and EDS analysis. The collective XRD analysis reveals the single-phase patterns corresponding to various dopants concentration in the powder system matrix. The calculated structural - auxiliary parameters viz. Lattice constants (a and c), cell volume (Vcell), X-ray density (dx), bulk density (db) and porosity (P) have been found in range; a = 5.8798–5.8321 Å, c = 43.7316–44.7214 Å, Vcell = 1309.303–1317.304 Å3, dx = 5.014–4.987 gm/cm3, db = 3.774–3.128 gm/cm3 and P = 0.247–0.37. The XRD results were supported by FESEM and TEM images, which showed the plate-like shape of particles. Unlike irregular grains, regular platelet-like grains were composed of several crystallites with almost parallel c-axis and this is the most suitable shape for microwave absorption. Fourier-transform infrared spectroscopy (FTIR) showed the location of the ions including their respective bonds within the structure of the lattice matrix and variation of ion concentration was depicted by EDS analysis of the powder matrix. The investigation of magnetic properties was done by vibrating sample magnetometer (VSM). The saturation magnetization (Ms) and coercivity (Hc) were found to be in the range of 34.29–43.711 emu/g and 16.27–299.441 Oe, respectively. The improved values of Ms and Hc mean that these powders can be used as pre-eminent contestant materials for perpendicular recording media (PMR) applications. In addition, the synthesized Co2Y-type nanohexaferrites were characterized for the Mössbauer analysis at room temperature. The normal Zeeman (six-line patterns) splitting confirms the hexagonal phase of synthesized nanohexaferrites.

Efficiently controlling crystallization and magnetic properties of nanostructured Nd-Ce-Fe-B ribbons via electron beam exposure

Electron beam exposure (EBE) has been implemented to synthesize Nd-Ce-Fe-B-based nanostructured magnetic materials with controllable morphology and tunable magnetic properties. Greatly reduced crystallization time of amorphous ribbons to about 0.1 s is achieved, which is by far the most effective method due to the effect of an extremely high heating rate. The extremely high heating rate gives rise to a huge temperature gradient in the annealed ribbons leading to platelet-like grains due to the oriented nucleation and growth under quasi-static thermal stress. It was found that the size and shape of the grains can be finely controlled by the beam current intensity. A coercivity as high as 12.9 kOe, and a maximum energy product as high as 15.4 MGOe are obtained in pure (Nd0.8Ce0.2)12.2Fe81.6B6.2 ribbons exposed to a beam current of 0.4 mA, without doping any other heavy rare earth or coercivity enhancement elements. A single magnetic domain covering many grains was observed by the Lorentz transmission microscope (LTEM). It was found that the improvement of the magnetic performance has a deep correlation with the achievement of a single domain structure. Our results demonstrate that EBE shows great advantages in preparing the high coercivity Ce-substituted Nd2Fe14B magnets due to higher efficiency and higher controllability than conventional furnace annealing.

Phase and film formation pathway for vacuum-deposited Cu2BaSn(S,Se)4 absorber layers

Earth-abundant copper barium thioselenostannate, $\mathrm{C}{\mathrm{u}}_{2}\mathrm{BaSn}{(\mathrm{S},\mathrm{Se})}_{4}$, absorbers have recently demonstrated promising optoelectronic and defect resistance properties for solar harvesting applications. The highest photovoltaic device efficiencies have been achieved in vacuum-based co-sputter deposited films, yet there is a tendency for a multilayer formation consisting of large, plateletlike surface grains and a smaller grain-sized underlayer (often accompanied by voids). In this work we use a combination of in situ and ex situ x-ray diffraction and scanning electron microscopy to unravel the coupling of phase evolution to film morphology. We find that Cu surface migration and associated Cu-rich phases play a defining role in determining the overall film structure.

Harmonized toughening and strengthening in pressurelessly reactive-sintered Ta0.8Hf0.2C-SiC composite

Ta0.8Hf0.2C-27 vol%SiC (99.0% in relative density) composite was toughened and strengthened via pressurelessly in-situ reactive sintering process. HfC and β-SiC particles were formed after reaction of HfSi2 and carbon black at 1650 °C. Ta0.8Hf0.2C was obtained from solid solutioning of HfC and commercial TaC. The β-α phase transformation of SiC proceeded below 2200 °C. High aspect ratio, platelet-like α-SiC grains formed and interconnected as interlocking structures. Toughness and flexural strength values of 5.4 ± 1.2 MPa m1/2 and 443 ± 22 MPa were measured respectively. The toughening mechanisms by highly directional growth of discontinuous α-SiC grains were crack branching, bridging and deflection behaviors.

Influence of substrate temperature on the physical properties of SnS2 thin films prepared using nebulized spray pyrolysis technique

Influence of substrate temperature on the physical properties of Tin disulfide (SnS2) thin films is investigated. X-ray diffraction studies revealed that the SnS2 thin films are preferentially oriented as (001) plane. SEM analysis showed that SnS2 thin films had platelet-like grains. EDAX analysis clearly confirms the presence of expected elements of tin and sulfur in appropriate proportions. Multiple interference effects were predominant in all these thin films in wavelength region of 500–1100 nm. The direct optical band gap of tin disulfide thin films had decreased from 3.26 to 2.7 eV with the increase in substrate temperature. Photoluminescence studies expose that the intensity of NBE emission peaks differs according to the substrate temperature. A minimum resistivity value of 2.19 × 101 Ω cm was obtained for the film grown at Ts = 250 °C. Hall Effect measurement exhibited that all the SnS2 samples had n-type conductivity. Raman spectra exposed that SnS2 films had a broad peak at 314 cm− 1.

The tunable magnetic properties and microstructures of Co–Ni double-substituted M-type Casrla hexaferrites

M-type hexaferrites with Co2+ and Ni2+ions substituting for Fe3+ ions (Ca0.30Sr0.35La0.35Fe12.0−x(Co0.5Ni0.5)xO19, 0.0 ≤ x ≤ 1.0) were prepared by the traditional solid state method. X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), physical property measurement system-vibrating sample magnetometer (PPMS-VSM) have been employed to study the microstructures and magnetic properties of hexaferrites. XRD patterns showed that the single magnetoplumbite phase is obtained if Co–Ni content (x) ≤ 0.4 and impurity phases are observed in the structure when Co–Ni content (x) ≥ 0.4. FE-SEM micrographs showed that the hexaferrites with hexagonal platelet-like grains is obtained. The saturation magnetization (Ms), remanent magnetization (Mr), Mr/Ms ratio, magneton number (nB), coercivity (Hc), magnetic anisotropy field (Ha) and first anisotropy constant (K1) decrease with increasing Co–Ni content (x) from 0.0 to 1.0. And our reported results with tunable Hc and Mr can be used for recording applications.

Influence of tin precursor concentration on physical properties of nebulized spray deposited tin disulfide thin films

ABSTRACTTin disulfide thin films were prepared with different molarities of tin species (MSn) at the optimized substrate temperature using the Nebulized Spray pyrolysis technique to obtain better crystallinity with mono phase thin films. The concentration of Tin IV chloride Penta hydrate precursor is varied from 0.05:0.4 to 0.25:0.4 (SnCl4.5H2O: thiourea) to achieve correct stoichiometry and to tune the concentration of Tin ions in the SnS2 thin films. These films were well adherent, uniform, and shiny. Lower concentrations of Tin yields highly textured SnS2 thin films with (001) crystallite orientation. On increasing the concentration, the multi-phases (SnS and Sn2S3) were found to be present along with SnS2 material. The platelet-like grains were observed from SEM analysis in these SnS2 films. Multiple interference effects were predominant in all these thin films in the wavelength region of 600–1100 nm. The direct optical band gap of tin disulfide thin films had decreased from 3.2 eV to 2.75 eV with an increase in MSn from 0.05 to 0.2 M, respectively, and further increased to 3.0 eV for 0.25 M concentration. Using Hall Effect measurement, the type of semiconductor is found to be of n-type. A minimum resistivity value of 2.19 × 103 Ω cm was obtained for the film grown at MSn = 0.2 M.

Effect of low-melting point phases on the microstructure and properties of spark plasma sintered and hot deformed Nd-Fe-B alloys

The effect of adding a low melting point Pr-Cu-Al alloy during spark plasma sintering of melt-spun Nd-Fe-B ribbons is investigated. Regions of coarse grains were reduced and overall grain refinement was observed after the addition of Pr68Cu25Al7, leading to an enhancement of coercivity from 12.7 kOe to 20.4 kOe. Hot deformation of the samples in the spark plasma sintering system resulted in the formation of platelet-like grains, producing crystallographic alignment and magnetic anisotropy. The hot deformation process improved the remanence and energy product but reduced the coercivity. The decrease of coercivity resulted from grain growth and aggregation of Pr and Nd elements at triple-junction phases.

Micromagnetic Simulations for Coercivity Improvement Through Nano-Structuring of Rare-Earth-Free L10-FeNi Magnets

In this work we investigate the potential of tetragonal L1$_0$ ordered FeNi as candidate phase for rare earth free permanent magnets taking into account anisotropy values from recently synthesized, partially ordered FeNi thin films. In particular, we estimate the maximum energy product ($BH$)$_\mathrm{max}$ of L1$_0$-FeNi nanostructures using micromagnetic simulations. The maximum energy product is limited due to the small coercive field of partially ordered L1$_0$-FeNi. Nano-structured magnets consisting of 128 equi-axed, platelet-like and columnar-shaped grains show a theoretical maximum energy product of 228 kJ/m$^3$, 208 kJ/m$^3$, 252 kJ/m$^3$, respectively.

Influence of precursor solution volume on the properties of tin disulphide (SnS2) thin films prepared by nebulized spray pyrolysis technique

Tin disulphide (SnS2) thin films have been deposited with various precursor solution volumes (5–25ml) by nebulized spray pyrolysis technique onto glass substrates. The X-ray diffraction studies revealed that the as-deposited SnS2 thin films were polycrystalline in nature and having a hexagonal structure with a single preferential orientation along (001) plane. SEM analysis revealed that all the thin films had platelet-like grains. The EDAX analysis confirmed the presence of tin and sulphur. Multiple interference effect was predominant in all these thin films in the wavelength region of 500–1100nm. Direct band gap values were found to decrease up to 2.67eV with the increase in precursor solution volumes from 5 to 20ml and increased further. All the SnS2 thin films were found to be n-type semiconductors. The better conductivity and mobility noticed at the precursor solution volume of 20ml are explained by carrier concentration and crystallites. The Activation energy of these films was determined by plotting a graph between log (resistivity) versus reciprocal temperature using a four-probe method.

Optimization of the Magnetic Properties of Hot Deformed Nd-Fe-B Magnets

We investigated the effects of density of Nd-Fe-B isotropic MQ2 counterparts and hot deformation parameters, including temperature and time, on the microstructure, (0 0 L) texture, and magnetic properties of anisotropic MQ3 magnets. A higher MQ2 density yields a more homogeneous density distribution throughout the MQ2 magnet. When the MQ2 density reaches 7.58 g/cm 3 , the grain size is as fine as 70 nm. After hot deformation, the length of the platelet-like grains in the MQ3 magnet can be as small as 300 nm when deformed at 780 °C for 120 s. An increase in the deformation time to 240 s gives more uniform MQ3 grain sizes throughout the magnet, resulting in higher values of remanent induction B r = 13.8 kG, intrinsic coercivity i H c = 15.7 kOe, and maximum energy product (B·H) max = 46.5 MG·Oe. Inhomogeneity in (0 0 L) texture and microstructure along the MQ3 thickness axis is inevitable after hot deformation. However, if 12.5% of the upper and lower surfaces of the MQ3 magnet, deformed at 780 °C for 120 s, are polished, outstanding magnetic properties can be achieved: B r = 14.7 kG, i H c = 15.8 kOe, and (B·H) max = 51.5 MG·Oe.

Densification, Microstructure and Mechanical Properties of Reactive Hot-Pressed ZrB<sub>2</sub>-ZrC-Zr Cermets

This study reviews densification behavior, microstructure and mechanical properties of the various composition ZrB2-ZrC0.6-Zr cermets prepared by reactive hot-pressing of Zr + B4C powder mixtures between 1673 K and 2173 K. During reactive sintering, densification consisted of two parts, one resulted from the volume contraction due to the conversion of Zr + B4C mixture into ZrB2 and ZrC0.6, other resulted from the shrinkage due to grain boundary diffusion and grain boundary migration that mostly contributed to the densification. Highly-dense ZrB2-ZrC0.6-Zr cermets were obtained for Zr + B4C mixtures at equal to or greater than 1673 K. The resulting ZrB2-ZrC0.6-Zr cermets consisted of platelet-like ZrB2 grains, equiaxed ZrC0.6 grains and intergranular Zr. The ZrB2 and ZrC0.6 grains were coarsened with increase of the excess Zr amount and/or sintering temperature. On the other hand, the flexural strength and fracture toughness of the cermets strongly depended on the excess Zr amount and/or sintering temperature. In addition, the crack propagation behavior of the cermets was associated with the excess Zr amount. The cracks directly propagated in the samples with less than 16 vol% Zr, however, the multiple cracking behavior was observed for the samples with equal to or greater than 16 vol% Zr.