Needle-like Grains Research Articles

Solidified characteristic and enhanced properties of Al0.5MnFeNiCu0.5/Al–Ni functionally gradient coating fabricated by laser cladding on AZ91HP

To ensure the high entropy effect of the coating, it is necessary to control the dilution of Mg during laser cladding process. Therefore, Al0.5MnFeNiCu0.5/Al–Ni functionally gradient coating was proposed in this work. More remarkable, the design of Al–Ni transition layer effectively prevented the dilution of Mg into Al0.5MnFeNiCu0.5 layer, and relieved physical and chemical differences between Al0.5MnFeNiCu0.5 layer and Mg alloy. Al0.5MnFeNiCu0.5 layer exhibited flower-like grain consisted of BCC phase. Al–Ni remelting layer crystallized as the fine snowflake-like grain. Al–Ni layer presented coarse needle-like grain morphology. Microhardness of Al0.5MnFeNiCu0.5 layer was about 8.2 times more than that of the substrate. Specifically, compared with Mg alloy and Al–Ni layer, the wear volume of Al0.5MnFeNiCu0.5 layer were decreased by 87.83% and 50.38%, respectively. The results of Polarization curve, Nyquist curve and Bode plot indicated that Al0.5MnFeNiCu0.5 layer displayed better corrosion resistance than Al–Ni layer and Mg alloy.

Modulating electrical response and impedance in Co–Cr substituted M-phase barium hexaferrites: Examining microstructure, grain boundaries, charge transport, and computational modeling

This study explores the influence of Co2+ and Cr3+ doping on the microstructure and electrical properties of Ba-hexagonal ferrite synthesized using the sol-gel method. X-ray diffraction (XRD) confirmed the formation of the anticipated hexagonal M-type crystal structure. Field emission scanning electron microscopy (FESEM) revealed the evolution of grain morphology with increasing doping levels, showcasing the formation of needle-like grains. Electrical characterization using an impedance analyzer investigated dielectric, impedance, electric modulus, and conductivity properties at room temperature. The analysis of the dielectric spectra indicated a decrease in dielectric constant and an increase in loss tangent with increasing dopant concentration. The electric modulus spectra provided evidence for non-Debye relaxation behavior, further supported by observations of relaxation processes at varying frequencies in the conductivity spectra. Additionally, an increase in doping led to a decrease in both relaxation time and AC conductivity. Electrochemical impedance spectroscopy (EIS) measurements yielded complex impedance curves. These curves exhibited good agreement with the values obtained through software-based simulations of grain and grain boundary characteristics. Furthermore, the distribution of grains and grain boundaries observed in FESEM micrographs aligned with the patterns predicted by the EIS software.

Structural elucidation, morphological properties, dielectric properties and their physical interpretation of cerium-substituted cobalt and barium-based M-type hexagonal nano ferrites

This research uses the sol–gel method to look into how adding Co2+ and Ce3+ dopant cations changes the structure, shape, and electrical properties of M-type Ba hexagonal ferrites that have been synthesized. x-ray diffraction (XRD) analysis confirms the successful formation of the targeted hexagonal M-type crystal structure. We observed a reduction in unit cell volume and lattice parameters as the dopant concentration increased, indicating the effective incorporation of dopant ions into the crystal lattice. When the doping process happened, needle-like grain shapes appeared, which could be seen with a field emission scanning electron microscope (FESEM). As the concentration of the dopant increased, the dielectric spectroscopic measurements revealed an increase in the loss tangent (tan δ) from 0.05 to 3.68, and a decrease in the dielectric constant (ε′) from 283 to 3.41. This suggests a reduction in polarization and dielectric permittivity, as well as increased energy dissipation within the material. The electric modulus spectra showed relaxation behaviour that was non-Debye-type, which is another sign that there are complex and multifaceted ways for charges to move. The measurements of relaxation time and AC conductivity showed that the relaxation intervals were not regular and that the conductivity dropped from 2.22*10–4 Ω−1m−1 to 1.4*10–7 Ω−1m−1 as the doping concentration increased. Based on these findings, it seems that the processes of conductivity and dielectric relaxation play a big role in how charges move around in the doped ferrites. We validated complex impedance data obtained through electrochemical impedance spectroscopy (EIS) software against calculated impedance values. The derived grain and grain boundary characteristics also agreed with the observed grain distribution and boundaries from the micrographs, further corroborating the analysis.

Microstructure and Phase Transformation Behavior of NiTiCu Shape Memory Alloys Produced Using Twin-Wire Arc Additive Manufacturing

NiTiCu thin walls were produced by twin-wire arc additive manufacturing (T-WAAM) using commercial NiTi and Cu wires as the feedstock materials. This approach aims to solve the problems typically associated with large phase transformation hysteresis in NiTi shape memory alloys. The microstructure, mechanical properties, and phase transformation behavior of the as-deposited NiTiCu alloy were comprehensively examined. The results revealed that the as-deposited NiTiCu alloy was well-formed, with its microstructure showed columnar, equiaxed, and needle-like grains, depending on the location within the deposited walls. The microhardness gradually increased from the first to the third layer. The Cu content was 20.80 at%, and Cu-based precipitates were formed in the as-deposited NiTiCu. The volume fractions and lattice parameters of the matrix and precipitates in the as-deposited NiTiCu material were analyzed using high-energy synchrotron X-ray diffraction. The martensitic phase was identified as a B19 crystal structure, and the as-deposited NiTiCu underwent a one-step B2-B19 phase transformation. The tensile strength and fracture strain were approximately 232 MPa and 3.72%, respectively. In particular, the addition of Cu narrowed the phase transformation hysteresis of the as-deposited NiTiCu alloy from 24.4 to 7.1 ℃ compared with conventional binary NiTi alloys. This study expands the potential of T-WAAM in modifying the phase transformation behavior of NiTi-based ternary alloys.

Effect Mechanism of α-Ferrite Sustained Precipitation on High-Temperature Properties in Continuous Casting for Peritectic Steel

Exploring the mechanism of the α-ferrite precipitation process on high-temperature properties plays an important guiding role in avoiding slab cracks and effectively regulating quality. In this work, in situ observation of the α-ferrite sustained precipitation behavior for peritectic steel during the austenitic phase transition process has been investigated using high-temperature confocal scanning laser microscopy. Meanwhile, the high-temperature evolution of the phase fractions during the phase transition process was quantitatively analyzed based on the high-temperature expansion experiment using the peak separation method. Furthermore, the high-temperature properties variations of the casting slab during the α-ferrite sustained precipitation process were investigated with the Gleeble thermomechanical simulator. The results show that the film-like ferrite precipitated along the austenite grain boundaries at the initial stage of phase transition, then needle-like ferrite initiates rapid precipitation on film-like ferrite when the average thickness reaches 15~20 μm. Hot ductility reached a minimum at the ferrite phase fraction fα = 10~15%, while high-temperature properties returned to a higher level after fα > 40~45%. The appearance of a considerable amount of needle-like ferrite and grain refinement effectively improves the high-temperature properties with the α-ferrite precipitation process advances.

Experimental and temperature field simulation study of Inconel 718 surface cladding based on vacuum electron beam heat source

By vacuum electron beam welding machine based on simulation of temperature field of NiCrBSi, experiment was conducted by vacuum electron beam surface cladding (VEBSC). The microstructure and friction wear properties of the specimens were analyzed by scanning electron microscope (SEM), electron backscatter diffractometer (EBSD), microhardness tester and friction wear tester under different welding beam currents (IW), respectively. The results show that the grain orientation in Inconel 718 in the rolled state is very dispersed and consists of equiaxed austenite grains (about 15 μm) with a high number of annealed twins. The internal orientation difference becomes relatively uniform after VEBSC, and a large number of elongated needle-like grains (about 200–300 μm) appear in the surface layer. At the same time, the low angle grain boundary of the clad layer (CL) of the specimen increases and then decreases with the increase of IW. When IW = 18 mA, the specimen surface hardness reaches a maximum value of 632.5 HV, and the friction coefficient is at least 0.25. The wear mechanism after cladding is dominated by plowing and abrasive wear to improve the wear resistance of the material. However, the high temperature oxidizing properties do not change much.

Anisotropic microstructure, properties and molecular dynamics simulation of CoCrNi medium entropy alloy fabricated by laser directed energy deposition

CoCrNi medium entropy alloy additive part was fabricated by laser directed energy deposition process. Based on an optimized additive manufacturing process parameters, the microstructure, tensile properties and corrosion performance in the XOY and XOZ planes were compared to learn the anisotropic properties of the additive part. The majority of the additive parts consisted of equiaxed grains, a small proportion consisted of elongated needle-like grains. The equiaxed and elongated needle-like grains in the XOY plane were finer compared to that in the XOZ plane. The corrosion electrochemical activity is uniform in the XOY plane, but varies at different heights in the XOZ plane base on scanning vibrating electrode technique results. Electron backscatter diffraction results near the fracture indicated a larger and relatively more homogeneous residual stress peak in the XOY plane. The tensile and yield strengths in the XOZ plane were lower than those in the XOY plane by approximately 98.5 MPa and 19.1 MPa. While the elongation in the XOZ plane was more than twice as high as that in the XOY plane. The reason for the anisotropic tensile behavior was the strong texture in the XOY plane and the relatively random grain orientation in the XOZ plane. Single crystal and polycrystalline molecular dynamics were used to simulate the anisotropic tensile properties in the XOZ and XOY planes. Single crystal simulation results showed that the maximum stress was 19.0 GPa and elongation was 13.0% when the stretching was along the [110] crystal orientation. The minimum stress was 17.1 GPa and elongation is 11.1% elongation when the stretching was along the [11 1‾] crystal orientation. Anisotropy existed for CrCoNi alloys in terms of tensile properties along different orientations. Polycrystalline simulation in the XOY plane results showed that the main cause of anisotropy between them was the tangling of the 1/6<112> dislocations and the 1/6<521> dislocations, which caused obstacles to dislocation motion and thus improved the strength of CoCrNi additive parts. High tensile strength in the XOY plane, not the XOZ plane, was attributed to 1/6<112> and 1/6<521> dislocation tangles at the (1 1‾ 0)/(115) planes.

Uncovering the white etching area and crack formation mechanism in bearing steel

The microstructure of a damaged bearing from the field was characterized in this work with the intention to better understand microstructural features behind formation of White Etching Cracks (WEC) in bearings. Microstructural characterization of the altered white etching area (WEA) involved conventional electron backscattered diffraction (EBSD), followed by transmission electron microscopy (TEM), and transmission Kikuchi diffraction (TKD). In addition, automated crystallographic orientation mapping in TEM was performed on lamellae from selected regions of the WEA extracted via focus ion beam milling. The results revealed that the orientation of detectable grains within WEA is similar to that of the vicinal bulk material. WEA consists of small spherical grains (average 30 nm) and the orientation of the grains varied significantly in the deformed zone, suggesting that recrystallization had occurred. The interface between bulk material and the deformed zone is very sharp. Furthermore, needle-like grains, most likely originating from the zone undergoing only modest levels of severe plastic deformation, occurred in WEA. The occurrence of different grain sizes in WEA and incomplete plastic deformation strongly support the hypothesis of WEC formation via severe plastic deformation followed by recrystallization.

Synthesis and characterization of Ti-WO3 films for electrochromic applications

In this work, tungsten oxide thin films with titanium dopant were deposited at various temperatures of substrate and oxygen partial pressures on silicon wafer and indium doped tin oxide glasses using reactive dc-magnetron sputtering. The main objective of the study is to investigate in detail and to discuss the effect of titanium and deposition parameters on morphological and electrochromic studies of the films. With the alteration of deposition parameters, the morphology changed from granular to coarse with coagulation of grains, and the titanium has significant impact in increasing the grain size. The titanium films incorporated, which are analyzed by an energy dispersive spectroscopy. The needle-like grains with columnar topography was observed, and having some voids over the surface analyzed with atomic force microscopy. The films exhibited excellent electrochromic properties. The films coloration efficiency was altered between 31.8 cm2/C to 101.70 cm2/C.

Scavenger-Supported Photocatalytic Evidence of an Extended Type I Electronic Structure of the TiO2@Fe2O3 Interface.

Heterostructures of TiO2@Fe2O3 with a specific electronic structure and morphology enable us to control the interfacial charge transport necessary for their efficient photocatalytic performance. In spite of the extensive research, there still remains a profound ambiguity as far as the band alignment at the interface of TiO2@Fe2O3 is concerned. In this work, the extended type I heterojunction between anatase TiO2 nanocrystals and α-Fe2O3 hematite nanograins is proposed. Experimental evidence supporting this conclusion is based on direct measurements such as optical spectroscopy, X-ray photoemission spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), and the results of indirect studies of photocatalytic decomposition of rhodamine B (RhB) with selected scavengers of various active species of OH•, h•, e–, and •O2–. The presence of small 6–8 nm Fe2O3 crystallites at the surface of TiO2 has been confirmed in HRTEM images. Irregular 15–50 nm needle-like hematite grains could be observed in scanning electron micrographs. Substitutional incorporation of Fe3+ ions into the TiO2 crystal lattice is predicted by a 0.16% decrease in lattice parameter a and a 0.08% change of c, as well as by a shift of the Raman Eg(1) peak from 143 cm–1 in pure TiO2 to 149 cm–1 in Fe2O3-modified TiO2. Analysis of O 1s XPS spectra corroborates this conclusion, indicating the formation of oxygen vacancies at the surface of titanium(IV) oxide. The presence of the Fe3+ impurity level in the forbidden band gap of TiO2 is revealed by the 2.80 eV optical transition. The size effect is responsible for the absorption feature appearing at 2.48 eV. Increased photocatalytic activity within the visible range suggests that the electron transfer involves high energy levels of Fe2O3. Well-programed experiments with scavengers allow us to eliminate the less probable mechanisms of RhB photodecomposition and propose a band diagram of the TiO2@Fe2O3 heterojunction.

Influence of calcined halloysite on technological & mechanical properties of wall tile body

ABSTRACT The effect of adding 0.1, 0.3, 0.6, 1.0 wt.% halloysite clay, which calcined at 600, 800, 1000 and 1200°C, to the standard wall tile slurry was studied. Wet milled halloysite was sieved with different sizes to examine the halloysite grain size effect. The granulated samples were pressed by applying a pressure of 30 MPa using a hydraulic press and made ready for sintering at 1150°C for 30 minutes. Detailed technological, mechanical and microstructural characterization studies were done on sintered samples. Compared to standard wall tile, almost all the halloysite added samples displayed similar technological properties but higher green and fired strength values. The produced sample with adding 0.6% halloysite (at 600°C calcined) by weight showed a higher firing strength with 28.75 MPa value than the minimum requirement (17.75 MPa). Observation of needlelike microstructure in the porcelain body led to establishing a simple relationship between the interlocking effects of thin needlelike mullite grains and increasing strength values. This study has shown that the addition of calcined halloysite may be an alternative to produce a thinner section wall tile product.

Stability conditions and compositional variations of deerite in high-pressure meta-ironstone during subduction–exhumation processes (SW Tianshan, China)

Index minerals in metamorphic rocks, such as coesite, glaucophane, or lawsonite, are of great importance to understand high-pressure (HP) to ultrahigh-pressure (UHP) metamorphism, the thermal gradient, and the geodynamics of subduction zones. Deerite is thought to be diagnostic for blueschist-facies metamorphism in cold subduction environments and a sensitive indicator of the oxygen fugacity (fO2) in Fe-rich rocks. However, little is known concerning its stability and compositional variation during subduction and exhumation cycles. In this study, we provide the first detailed investigation of deerite in eclogite-facies meta‑ironstones (deerite–garnet riebeckitite) from the Southwestern Tianshan (U)HP metamorphic belt. Petrological observation and textural evidence suggest that the meta‑ironstones –enclosing eclogite blocks– form part of an initially coherent volcano-sedimentary sequence that underwent a common tectono-metamorphic evolution, including HP metamorphism and subsequent exhumation. Two types of deerite, which display a different texture (inclusion vs. matrix) and composition (TiO2 content), occur in the deerite–garnet riebeckitite. Dee_1 and aegirine–augite appear exclusively as fine-grained inclusions in garnet, and together with garnet, riebeckite, quartz and magnetite form the peak metamorphic mineral assemblages at P–T conditions of ~510 °C and 2.6 GPa. Matrix deerite (Dee_2), on the other hand, mainly occurs as coarse-grained rods and acicular needle-like grains in quartz, and rarely as inclusions in riebeckite and garnet intimately in the riebeckitite, representing the blueschist-facies retrogression of the meta‑ironstones during exhumation. The garnet–clinopyroxene oxybarometer and thermodynamic calculations show that the fO2 of the deerite–garnet riebeckitite increases from ΔFMQ–0.64 at the peak eclogite-facies stage to ΔFMQ+1.5 at the blueschist-facies retrogression. This fO2 variation corresponds to the chemical variation of deerite, whereby the TiO2 content increases gradually from <0.1 wt% in the Dee_1 in garnet to about 5 wt% in the matrix Dee_2. Our study reveals the detailed metamorphic P–T–fO2 evolution of the prograde eclogite- and retrograde blueschist-facies deerite-bearing meta‑ironstones during subduction–exhumation processes. This study further emphasizes the potential of deerite to reveal the P–T–fO2 evolution of subduction-related high-pressure rocks.

Sintering Behavior and Properties of Reaction-Bonded Silicon Nitride

The influence exerted by the conditions of the preliminary synthesis of Si3N4 by nitridation at 1350 and 1400°С and additional high-temperature sintering at 1800 and 1900°С on the properties of reaction-bonded silicon nitride was studied. Secondary silicon nitride (β-Si3N4) formed in the course of nitridation consists of needle-like grains, which reinforce the material and impart to it additional mechanical strength. The microstructure and phase composition of the silicon nitride material at different initial ratios of silicon and silicon nitride were studied. The materials obtained approach liquid-phase-sintered and hot-pressed silicon nitride in the mechanical properties.

Enhanced superconducting performance in solution-derived YBa2Cu3O7−δ films using parallel ion-beam structure modification method

Surface modification of superconductors has been extensively researched. However, such modification usually degrades the superconducting properties by creating rough surface morphologies and non-superconducting phase impurities, with the exception of the antidot method modification. Here, a new parallel ion-beam structure modification (PISM) method proves extraordinarily effective in improving the superconductivity of solution-derived YBa2Cu3O7−δ (YBCO) films. Experimental results demonstrate that the surface morphologies of the treated YBCO films become smoother than the pristine samples, and large-sized pores, needle-like a-axis grains, and/or secondary-phase impurities are almost completely removed. Treatment by the PISM method affords remarkable increase ratios ΔJc of the critical current density by 128.9% or more, where greater improvements are achieved by increasing the Ar+ ion bombardment time. The current-carrying capacity is improved by newly generated impurities, i.e., Ba‒Cu‒O phases acting as Δl volume pinning centers, and drastic shortening of Cu‒O bonds derived from the non-uniform compressive strain.

Electrodeposition of Tin Selenide from Oxalate-Based Aqueous Solution

In this work, we report a study of the electrodeposition of SnSe. Considering the difficulty to stabilize the baths containing Sn(II) and Se(IV) precursors, we investigated the benefits of using sodium oxalate as a complexing agent. Preliminary cyclic voltammetric (CVs) experiments were performed to study the electrochemical behavior of tin and selenium redox systems within this specific electrolyte solution. The study revealed that the oxalate reagent stabilizes the bath chelating Sn(II) and then preventing the precipitation of SnO2. From the CVs, a growth mechanism is proposed and a synthesis potential window is defined, in which the electrodeposition of SnSe films was investigated. Between −0.5 and −0.6 V vs sat. AgCl/Ag, the deposits exhibit typical polycrystalline SnSe needle-like grains. SnSe was shown by Raman spectroscopy and the XRD patterns display an orthorhombic single-phase for this compound. Additional Mössbauer analyses confirm the presence of Sn(II), which is in good agreement with the chemical composition of SnSe films. Moreover, a cross-analysis between the methods shows also the presence of SnSe2 in minor proportion. The depth profile analyses of the samples reveal an in-depth homogeneity as well as the presence of oxygen at the layer surface.

A New Sight of the Growth Characteristics of Solidified Al3Ni at the Liquid–Solid Interface by Synchrotron Radiography and 3D Tomography

The growth mechanisms of single- and variant-flake Al3Ni phases at the liquid Al/solid Ni interface during solidification were investigated by synchrotron radiography and 3D tomography. The single-flake Al3Ni in the form of an elongated diamond rod evolves from one needle-like grain. The variant-flake Al3Ni is formed by coalescence of several needle-like Al3Ni grains, and its growth is dominated by the creation and propagation of a pair or groups of screw dislocations with opposite signs.

Silicon substrate orientation influence on structural and magnetic properties of BaFe12O19 thin films obtained by RF magneton sputtering

In this work, the fabrication of BaFe12O19 (BaM) thin films by radio-frequency sputtering and the influence of substrate orientation on structural, microstructure and magnetic properties were carried out. Measurements pointed out the deposition time and power have no significant effect over stoichiometry in the studied condition, producing films with satisfying Fe:Ba rate confirmed by EDX analysis. The orientation of the Si substrate showed to be essentially correlated with in-plane orientation of BaM phase. Both Si (1 0 0) and (1 1 1) substrates privileged in-plane orientation of the c-axis of BaM and atomic force microscopy found needle-like grains spread randomly onto substrates, although Si (1 1 1) substrate exhibited higher magnetic anisotropy.

An efficient method for recycling spent residue cat-cracking catalysts (SRC) to prepare broadly-applicable mullite-based wear-resistant ceramics

Spent residue catalysts (SRC) of fluid cat-cracking were used as raw materials for the preparation of wear-resistant ceramics. The starting material was wet-milled and then dried to obtain semi-dried powders. The resultant powder was pressed into various shapes and sintered at various temperatures (1300 to 1450 °C). The bulk density and linear shrinkage of the samples increased as the temperatures rose, while the apparent porosity and water absorption behaved in a reverse manner. Based on the results, the specimens sintered at 1450 °C appeared to be the best alternatives for the preparation of the wear-resistant ceramics. The results also revealed that pre-calcination has no significant effect on the final properties of the ceramic products. The XRD results approved that mullite is the only crystallized phase in the specimens sintered at 1450 °C. Moreover, the absence of vanadium and nickel-based phases in the XRD pattern indicated that these elements had been stabilized in the glassy phase. SEM images displayed the presence of needle-like mullite grains, in agreement with the XRD results. Additionally, SEM images illustrated that the fractures, appeared after the wear test, were inter-granular and may have been resulted from the well-controlled sintering conditions. Generally, the results of this study suggest a cleaner method for converting the SRCs to wear-resistant mullite-based ceramics with a wide range of industrial applications.

Influence of substrate temperature on the chemical, microstructural and optical properties of spray deposited CH3NH3PbI3 perovskite thin films

Methylammonium lead iodide (CH3NH3PbI3) perovskite has been proposed as a key component of thin film solar cells. In this work, the influence of substrate temperature on the properties of spray deposited CH3NH3PbI3 thin films was investigated. The main purpose of this work was to determine the best conditions to deposit and crystallize CH3NH3PbI3 perovskite thin films in a single step. An automatic spray system was used for depositing a solution of lead iodide and methylammonium iodide onto heated substrates under ambient conditions for just one second. After deposition the samples were held at the same temperature for 30 s. The substrate temperature varied from 60 °C to 140 °C. Substrate temperatures in the low range (60 °C–80 °C) led to films with needle-like or dendritic grains, extra phases, and poor coverage due to the low solvent evaporation rate, while depositions above 120 °C led to thermal decomposition of the film. The best results were obtained for substrate temperatures of 100 °C and 120 °C, which produced dense perovskite films with large equiaxed grains and good coverage. The transmittance spectra of these films showed the perovskite characteristic absorption edge at 780 nm. In addition, the Fourier-transform infrared spectra did not show any peaks associated with the solvent, confirming its evaporation and indicating that a 31 s overall processing time is enough to achieve a full perovskite crystallization.

Synergistic effects of particle and transient heat loads on ITER-grade tungsten

ITER’s divertor will have to sustain high particle and heat loads. Tungsten has been chosen as plasma facing material for the entirety of ITER’s divertor. Therefore, it is important to study the behavior of ITER-grade tungsten under fusion relevant loads. In this work, tungsten samples with two different microstructures were studied, one with needle-like grains transversal to the surface, and the other with larger, isotropic grains obtained after recrystallization. The samples were exposed to a steady state plasma and a pulsed laser in the linear plasma device PSI-2 to simulate the conditions of the divertor in a fusion reactor. The results show that the transversal samples have a higher damage threshold, but at higher power density and pulse numbers, the damage observed, as well as the surface roughness, is similar. The recrystallized samples displayed a shallower crater depth, which might be an important factor to be considered when selecting a material for ITER and should be studied further.