Sintering Method Research Articles

The effect of MnO2 additive on the microstructure and mechanical properties of magnesium aluminate spinel

AbstractIn this study, varying amounts of MnO2 up to 5 wt.% were added to magnesium aluminate spinel (MA) bodies using a solid‐state sintering method at 1200–1600°C. The effect of MnO2 addition on the phase composition, microstructure, distribution of elements, and ionic valence of MA was investigated via X‐ray diffraction, scanning electron microscopy, energy‐dispersive spectroscopy, and X‐ray photoelectron spectroscopy, respectively. The results showed that Mg2+ ions in MA crystals were replaced by Mn2+ ions, resulting in the formation of the (Mg1‐xMnx)Al2O4 solid solution. The distorted crystal structures promoted the sintering reactions, and the mechanical characteristics of MA were greatly improved by the solid solution strengthening process. When the additive amount of MnO2 was 5 wt.% and the sintered temperature reached at 1600°C, excess manganese ions hardly dissolved into the lattice of MA. And these ions were only distributed at the grain boundaries of MgAl2O4, forming a “barrier” that hindered the migration and diffusion of particles, thereby suppressing the sintering process and weakening the mechanical strength of MA.

Evaluation of the dielectric, and piezoelectric properties and optimizing the figure of merit of the 0–3 KNN-0.8ZnO/PVDF-HFP piezoelectric composite by the Taguchi method

Piezoelectric ceramic and composite materials are attractive for various applications, but they can be challenging to process. In this research, KNN-0.8ZnO with high density (ρth=95 %), favorable microstructure, and suitable dielectric and piezoelectric properties (K=875, d33=125 pC/N, tanδ=0.01) was first synthesized. Additionally, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) copolymer, known for its advantageous piezoelectric and mechanical properties, was selected as the polymer phase. subsequently, the KNN-0.8ZnO/xPVDF-HFP composite samples with a 0–3 connectivity pattern were made with the cold sintering method. The Taguchi design of experiment (DOE) was employed to determine the optimal condition for maximizing the figure of merit (FOM). Furthermore, an analysis of variance (ANOVA) was carried out to evaluate the significance of individual factors on each measured property. Phase identification was performed using X-ray diffraction (XRD) analysis, while the microstructure was examined using scanning electron microscopy. Among the different composite samples fabricated using the L9 orthogonal array (OA) of the Taguchi method, the KNN-0.8ZnO/20PVDF-HFP composite containing 20 wt% polymer phase, that was cold-sintered under a pressure of 400 MPa at 200 ͦC for 2 h, exhibited the highest FOM value of 1.945Pm2/N. This result aligns with the optimal conditions predeicated by the Taguchi DOE method. The compressive strength of the KNN-0.8ZnO/20PVDF-HFP composite was assessed through a compression test, yielding a value of 207 MPa, while the elastic modulus was approximately 3 GPa. The findings of this study demonstrate that the cold sintering method is an effective approach for producing dense piezoelectric composites with favorable electrical and mechanical properties, along with a high FOM for energy harvesting applications.

Asymmetric porous polybenzimidazole membrane with tunable morphology for vanadium flow battery (VFB)

Polybenzimidazole (PBI) membranes have attracted much attention for flow batteries due to their good chemical stability. However, the high area resistance (AR) of dense PBI limits its further development in VFBs. Herein, we design a sintering method to remove the phthalates with different molecular structures in the ternary system (PBI as polymer, N-methylpyrrolidone as solvent, and phthalates as non-solvent). Asymmetric PBI membranes with adjustable and disconnected pores, as well as ultrathin-dense layers, are prepared. This series of porous membranes shows excellent overall performance in VFBs. Among them, the porous NPBI-DBP-200 membrane (0.139 Ω cm2) with DBP as the non-solvent exhibits a lower AR compared to the dense NPBI (0.489 Ω cm2). At a current density of 200 mA cm−2, the energy efficiency (EE) of a single cell assembled with the NPBI-DBP-200 membrane (EE = 78.26 %) has improved by 26.37 % compared to the dense NPBI membrane (EE = 61.93 %). In addition, the porous NPBI-DBP-200 membrane has excellent in-situ stability, and the single cell can operate stably for 1800 cycles at the current density of 120 mA cm−2. This work presents a novel, easy-to-use technique for preparing high-performance porous PBI membranes with adjustable pore morphology.

Scintillator application of CsPbBr3 quantum dots-embedded SiO2 glasses

CsPbBr3 quantum dots-embedded SiO2 glasses were synthesized by the spark plasma sintering method as novel scintillators for γ-ray detectors. Their optical and scintillation properties were investigated to examine the scintillation performance. The X-ray diffraction patterns observed a halo peak of the SiO2 glass phase and diffraction peaks of CsPbBr3. An emission peak due to CsPbBr3 quantum dots was detected at around 515 nm in both photoluminescence (PL) and scintillation spectra. The PL and scintillation decay time curves included a component of nanosecond order, resulting from CsPbBr3 quantum dots. Under γ-ray irradiation from 137Cs, the light yield (LY) of the 0.2% CsPbBr3-embedded SiO2 glass was 150 photons MeV−1.

Study on liquid-phase sintering and magnetic properties of SLA-printed Mn-Zn ferrite ceramics

To obtain Mn-Zn ferrite magnetic ceramic parts with good densification and magnetic properties, a study was conducted. Mn-Zn ferrite magnetic ceramic parts with a solid particle content of 58 vol% were prepared using stereolithography (SLA). The SLA-cured ceramic blanks were degreased and sintered. The degreasing process for Mn-Zn ferrite parts was optimized using a direct heat degreasing method, resulting in a suitable process for the ferrite magnetic ceramic paste system. The method of liquid phase sintering is proposed for sintering the degreased ferrite parts. The study investigated the impact of the content of accelerant, sintering temperature, and holding time on the density and magnetic properties of Mn-Zn ferrite parts. The optimal parameters were found to be a firing aid content of 3 wt%, a sintering temperature of 900 °C, and a holding time of 90 min. Under these conditions, the parts exhibited a density of 4.43 g/cm3, densification of 91.4 %, saturation magnetization strength of 64 emu/g, and coercivity of 10 Oe. Finally, the sintering control mechanism of SLA-printed ferrite magnetic ceramics was analyzed. The study revealed the grain growth process and magnetization principle of Mn-Zn ferrite during liquid phase sintering. This research provides guidance for the subsequent photocuring printing and degreasing sintering of Mn-Zn ferrite ceramics. Additionally, Mn-Zn ferrite magnetic ceramic parts prepared by the SLA method also hold a wide application prospect in various precision electronic components.

Experimental investigation of heat treatments on the mechanical performance of grade 300 maraging steel strut-based lattices

Lightweight and strong components are essential for reducing energy consumption and enhancing efficiency. Lattice structures are one such geometry utilized to achieve weight reduction. This study investigates the mechanical properties of various lattice structures fabricated from Maraging Steel (EOS MS1) using the Direct Metal Laser Sintering (DMLS) method. The samples include three distinct cellular geometries: body-centered cubic (BCC), face-centered cubic (FCC), and octet truss configurations, which are subjected to tensile and compressive tests. The primary goal of this research is to evaluate the impact of heat treatment on the mechanical properties of cellular architecture under tensile and compressive loading conditions. Destructive, nondestructive testing, and simulation results were also obtained from different heat treatment processes. It was found that the age-hardened specimens performed the best overall in terms of ultimate tensile/compressive strength and elongation. The top-performing topologies in compression and tension were found to be the octet structure, as they were able to withstand the most loading and straining when compared to the other specimens.

Preparation of porous composite coatings to suppress surface charge movement and reduce electrical resistivity

In this work, Cr2O3/TiO2 composite coatings were prepared on α-Al2O3 insulating ceramic matrix surface by screen printing and solid phase sintering methods to yield an average film thickness of about 14.10 μm. Scanning electron microscopy (SEM) revealed changes in the pore structures of the coatings at different TiO2 contents. The atomic force microscopy (AFM) analysis of the coating surface roughness suggested a TiO2 content of 0.025 mol to yield the best surface roughness and pore structure of the coating. The calculation showed an increase in the energy level of the deep trap center on the surface from 1.506 eV to 1.547 eV, reaching a maximum. The surface resistivity of insulating ceramics decreased from 1016 Ω to 1012 Ω. The formation of deep surface traps and the decrease in surface resistivity promoted charge dispersion and suppressed the formation of flashover channels, effectively improving the surface flashover voltage of the ceramics.

Significantly enhanced piezoelectric response in Aurivillius Bi3TiNbO9 ceramics simply by Ce doping

Bi3-xCexTiNbO9 (BTN-100xCe, x = 0, 0.01, 0.03, 0.05, 0.07, 0.09, 0.11) piezoelectric ceramics with ultra-high Curie temperature were fabricated by a solid-state sintering method, and the effect of Ce doping on the structure, dielectric and piezoelectric properties of the ceramics was investigated. All ceramic samples possess a single Aurivillius phase and Ce ions enter both A- and B-sites. Dense microscopic morphology with a remarkable decrease of grain size can be observed due to Ce doping. The resistivity markedly increases after Ce modification, and a significantly enhanced piezoelectric constant d33 of 17.1 pC/N can be achieved in the optimized BTN-7Ce ceramics, which is nearly 6 times that of pure Bi3TiNbO9 (d33 ≈ 3 pC/N). In addition to ultra-high Curie temperature (TC = 886.5 °C) and relatively high resistivity (ρ = 1.2 × 106 Ω cm @ 500 °C), the BTN-7Ce ceramics should be very promising for piezoelectric sensor under the application in high temperature conditions.

Preparation of porous (Mo2/3Y1/3)2AlC and its hydrogen evolution reaction performance

Porous (Mo2/3Y1/3)2AlC MAX phase ceramic was prepared by reaction sintering method using Mo, Y, Al, and graphite powder as raw materials. The influence of changes in Al content on the purity of the obtained samples was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Archimedes method, and bubble point method. The conditions for obtaining a pure phase were identified, and the transformation path of the phase during sintering and the mechanism of pore formation were provided. The linear sweep voltammetry (LSV) cure and cyclic voltammetry (CV) cure of MAX were tested using an electrochemical workstation. It can be calculated that MAX exhibits good hydrogen evolution reaction (HER) performance under alkaline conditions due to its high electrochemical active surface area (ECSA) of 373.2 and small Tafel slope of 41.7 ​mV·dec−1.

An Investigation on the Effect of TiC Additive on the Microstructural and Mechanical Properties of Ultra-High Temperature ZrB2-SiC-Based Ceramic Composite by Multi-Step Spark Plasma Sintering Method

An Investigation on the Effect of TiC Additive on the Microstructural and Mechanical Properties of Ultra-High Temperature ZrB2-SiC-Based Ceramic Composite by Multi-Step Spark Plasma Sintering Method

Effect of Y2O3 on thermophysical parameters and mechanical properties of Al-Al2O3 composites and compatibility with high temperature Al-Si alloys

Abstract Al-Al2O3 is a crucial encapsulation composite used in solar thermal storage systems. This study utilized Al and Al2O3 powders as raw materials, with Y2O3 serving as a sintering aid, to prepare Al-20Al2O3-xY2O3 composites (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 wt%) through the cold pressure sintering method. The latent heat, thermal conductivity, and bending strength of the Al-20Al2O3-xY2O3 composites were measured. The compatibility of the composites with Al-12 wt%Si alloys was analyzed. Furthermore, the relationships between thermophysical parameters, mechanical properties, compatibility, and microstructure were explored. The oxidation mechanism of Al and the wetting angle of the composites with Al-12Si were simulated using LAMMPS software. It was concluded that with an increase in Y2O3 content, the bending strength, thermal conductivity, and compatibility of the composites initially increased and then decreased. The Al-20Al2O3-0.2Y2O3 composite exhibited the least porosity, highest bending strength (76.32 MPa), and thermal conductivity (46.82 W/(m·K)). In compatibility testing, the diffusion distance of Si atoms was shortest (90 μm) in the Al-20Al2O3-0.2Y2O3 composite. Moreover, this composite had the largest wetting angle (88°) with the Al-12Si alloy, resulting in good compatibility between them.

Epoxy Composite Films Filled with Sintered Multifaceted Boron Nitride for Thermal and Dielectric Applications

The miniaturization of electronic devices has led to an increase in power density and functional integration, resulting in rapid heat accumulation that adversely affects operational stability and service life. Dielectric composite films with excellent thermal conductivity and insulating properties are highly desired for addressing thermal management issues in electronic packaging applications. Hexagonal boron nitride (h-BN) is a promising filler for such composites due to its outstanding thermal conductivity, insulating properties, and chemical stability. However, the inherent platelike structure of h-BN causes significant anisotropy and poor miscibility with polymers, limiting the uniform conduction of heat. This study proposes a high-temperature sintering method that transforms flaky h-BN plates into irregular multifaceted particles. This transformation reduces thermal anisotropy and creates uniform heat conduction pathways. The resulting sintered BN/Epoxy (s-BN/EP) composite films exhibit exceptional thermal conductivity, with in-plane thermal conductivity increased by 36% to 6.0 W m-1 K-1 and through-plane thermal conductivity increased by 39% to 1.2 W m-1 K-1 compared to pristine h-BN/epoxy composites. Moreover, s-BN/EP films could maintain low dielectric constant (Dk, 3.22) and dielectric loss (Df, 0.015) at 5 GHz. This innovative approach provides a significant advancement in the development of high-performance insulating polymer composites, offering a promising solution for thermal management in high-power-density electronic packaging.

(La0.2Ce0.2Gd0.2Er0.2Sm0.2)2Zr2O7 High-entropy ceramic-glass composite coating with a high corrosion resistance

In this work, a new type of high-entropy ceramic powder (La0.2Ce0.2Gd0.2Er0.2Sm0.2)2Zr2O7 was synthesized by sol-gel method and high-temperature sintering (1000 °C) method. Combing (La0.2Ce0.2Gd0.2Er0.2Sm0.2)2Zr2O7 and glass powder to prepare high-entropy ceramic-glass composite coating. The composite coating exhibits excellent seawater corrosion resistance and high-temperature resistance performance. The impedance values of composite coating are 2.36 × 106 Ω cm2 in 3.5 % NaCl solution for 24 h. The high-entropy ceramic-glass composite coating could withstand the high temperature of 600 °C for 30 days and remains tight and intact with stainless steel without falling out. This work shows that the (La0.2Ce0.2Gd0.2Er0.2Sm0.2)2Zr2O7-glass composite coating can provide long-term high-temperature and seawater corrosion protection for stainless steel and has good application prospects in the field of marine corrosion protection.

Large dielectric properties of niobate-titanate glass ceramics prepared by powder sintering method

Niobate-titanate glass-ceramics with large dielectric constant were prepared by the dual optimization strategy employed——glass powder sintering method and simultaneous introduction of multiple nucleating agents. The study delved into the crystallization and microstructure of the glass ceramics, with a subsequent characterization of their dielectric and ferroelectric properties. In this investigation, the crystalline phase underwent a transformation from the Pb2Nb2O7 phase of G700 glass ceramics to the coexistence of (Pb, Sr)TiO3 and (Ba, Sr, Pb)Nb2O6 phase of G1100 glass ceramics. The crystal phase content exhibited a notable increase from 29 % to 82 %. The relative density of the glass ceramics reached a high of 99.4 %. The maximum dielectric constant recorded was 1493, accompanied by a maximum energy efficiency of up to 88.0 %. These results underscore the potential of glass ceramics as a promising material for Multilayer Ceramic Capacitor (MLCC) dielectric layers.

Arc erosion behaviour of Cu–diamond composites at different load voltages in air atmosphere

ABSTRACT To investigate the arc erosion performance of Cu–diamond composites, Cu–5vol.-% diamond composites were fabricated using the hot-pressing sintering method. Compared to pure copper, Cu–5vol.-% diamond composites exhibited improvements in Brinell hardness of 60.1 HB. The relative density and electrical conductivity of Cu–5vol.-% diamond composites were 97.54% and 83.29% IACS (International Annealing Copper Standard), respectively, with no significant decrease compared to pure copper. The thermal conductivity was 423.48 W·(m·K)−1, showing a slight enhancement. The effect of different load voltages on the arc erosion behaviour of Cu–5vol.-% diamond composites was investigated. Experimental results indicated that as the voltage rose from 3 to 7 kV, the breakdown strength decreased from 7.164 × 106 V m–1 to 2.535 × 106 V m–1, while the arc duration increased from 21.752 × 10−3 s to 28.864 × 10−3 s, and the breakdown current rose from 10.8 to 27.2 A. Additionally, the presence of diamond particles enhanced the viscosity of the molten pool, thus the splashing phenomenon of copper liquid during arc discharge was not obvious, indicating that the material loss was small. Few cracks and holes were detected. The Cu–5 vol.-% diamond composites possess good resistance to arc erosion.

Simultaneously improving the strength and ductility of an oxide dispersion-strengthened high-entropy alloy by employing innovative precursors for oxide formation

The engineering of a composite microstructure, achieved by coupling heterogeneous grain distribution with oxide dispersion, has been demonstrated as an effective strategy for enhancing the strength-ductility synergy of alloys at both room and elevated temperatures. The effectiveness of this approach is strongly correlated with the micro-features of dispersed oxides. In this study, we selected the Ni38Co20Cr20Fe18Ti4 high-entropy alloy (HEA) as the base material, which could achieve the desired composite structure through preparation using mechanical alloying and spark plasma sintering methods. Our primary objective was to investigate the effects of incorporating Y2O3 or utilizing hydrides (TiH2 and YH3) as alternative precursors on the modification of oxide precipitates, evolution of a bimodal grain microstructure, and alteration in mechanical properties for the oxide dispersion strengthened (ODS) HEA. The results show that the incorporation of Y2O3 promotes the formation of ultrafine and semi-coherent Y2Ti2O7 ternary oxide particles, in addition to the pre-existing coarse binary TiO in the HEA matrix. Moreover, this leads to a significant increase in the fraction and a decrease in the average size of ultrafine grains (UFGs) within the bimodal microstructure. Notably, utilizing Ti- and Y-hydrides instead of Y2O3 and Ti as oxide-forming precursors within an equivalent composition remarkably amplifies the precipitation proportion of Y2Ti2O7 among dispersoids while further refining UFGs. The ODS-HEA synthesized using hydrides exhibits a simultaneous enhancement of 12 % in yield strength and 13 % in elongation to fracture, compared to that prepared from Ti and Y2O3. This intriguing phenomenon primarily arises from the heightened strengthening and toughening contributions, facilitated by the increased precipitation of advantageous Y2Ti2O7 nanoparticles.

Capacitive voltage effect at a resistive sintering system container and its electrical model

Abstract The electric current activated/assisted sintering (ECAS) method enables various kinds of materials to be produced much faster and environmentally friendly compared to conventional sample production systems. The main handicap of this system is that the heating regime varies according to the material type even the chemical composition of the same type of material and causes partial melting due to the sudden current flow. Previously, the ECAS output equivalent circuit is modeled as a temperature-dependent resistor in the literature. This study shows that it is insufficient to model the ECAS output consisting of a container and two stiffs as a resistor considering experimental waveforms. We report the discovery of a capacitive effect at the output of the ECAS system that has not been reported before. We have given an equivalent electrical circuit for the ECAS system output and examined the effect’s temperature dependence. The circuit model, which consists of a parallel resistor-capacitor (R p-C) circuit in series with another resistor (R s), is suggested for the container and the stiffs. By using the experimental data, the equivalent circuit parameters are calculated by curve-fitting. The temperature dependence of the equivalent circuit parameters is also examined. Possible explanations for the capacitive effect are given. Such a model and further examining the effect may help design better ECAS systems.

Method for profile reconstruction of the workpiece surface during groove micromilling

A leading trend in modern industry is hybrid manufacturing methods. The intention is to integrate additive and subtractive methods into a single machine. In such a process, it is difficult to evaluate the quality of the manufactured component between successive processes. A solution that would make it possible to determine the quality of a component produced by incremental technologies on the basis of forces recorded in a machining process is not yet available. In the present study, an attempt was made to reconstruct the surface of the machined workpiece solely on the basis of recorded forces during the groove micromilling process. A workpiece with a known surface geometry in the form of a sinuous wave was machined. The geometry of the workpiece corresponded to a structure typical of the selective laser sintering method for metallic powders. A process conducted with two different axial cutting depths was considered. The reconstructed surface profiles were evaluated by comparative analysis with the real machined surface.

Improving properties of boron carbide (B4C) with silicon doping and titanium diboride addition

In this research, B4C-TiB2 composites were successfully fabricated via the spark plasma sintering method. First, the TiB2 source effect on the B4C-TiB2 composites was investigated using commercially available TiB2 and in-house synthesized TiB2. Subsequently, the effect of Si/B co-doped B4C on composite ceramics was studied, followed by examining the samples' microstructure and elastic and mechanical properties. The results showed that B4C-TiB2 composites made with in-house TiB2 powder obtained higher relative density and more desirable elastic and mechanical properties than samples made with commercial TiB2. In-house TiB2 and Si/B-B4C composites provided more properties improvement overall. The elastic modulus, Vickers hardness, and fracture toughness values of Si/B co-doped samples were 493 GPa, 30.09 ± 1.97 GPa, and 4.31 ± 0.74 MPa m1/2, respectively. Additionally, the amorphization of the TiB2-B4C composite decreased with Si/B co-doping.

Study on the mechanism of potassium fluoride, magnesium fluoride and calcium fluoride on the crystal morphology and sintering performance of fluorapatite functional glass-ceramics

Fluorapatite glass-ceramics were prepared at lower temperatures by atmospheric pressure sintering method using KF, MgF2 and CaF2 as additives, respectively. Using XRD, SEM and mechanical property test to justify the effect of different fluorides on the sintering properties of fluorapatite composites. The results show that fluoride can be used as nucleating agent, react with wollastonite and phosphate glass to crystallize rod-like fluorapatite phase during heat treatment. The crystallization mechanism of fluorine-containing glass-ceramics was analyzed by crystallization thermodynamics and crystallization kinetics. KF with lower melting point is beneficial to promote the crystallization reaction and improve the morphology stability of the glass ceramic composite, but the volatile gas released during the reaction will affect the mechanical properties of it, resulting in a flexural strength of only 11.81 MPa at 900 °C. For the samples supplemented with MgF2 and CaF2, because of the formation of polycrystalline phase systems, the flexural strength of the composite at 900 °C increases to 62.79 and 52.6 MPa, respectively.