Search Results (224)

This study investigates the effect of boron carbide (B₄C) ceramic reinforcement on the microstructural, mechanical, electrical, and electrochemical properties of CoCrMo, Ti, and 17-4 PH alloys produced via powder metallurgy for potential biomedical applications. A systematic experimental design was employed, incorporating varying B₄C contents into each matrix through mechanical alloying, cold pressing, and vacuum sintering. The microstructural integrity and dispersion of B₄C were examined using scanning electron microscopy. The performance of the materials was evaluated using several methods, including Vickers hardness, pin-on-disk wear testing, ultrasonic elastic modulus measurements, electrical conductivity, and electrochemical assessments (potentiodynamic polarization and EIS). This study’s findings demonstrated that B₄C significantly enhanced the hardness and wear resistance of all alloys, especially Ti- and CoCrMo-based systems. However, an inverse correlation was observed between B₄C content and corrosion resistance, especially in 17-4 PH matrices. Ti-5B₄C was identified as the most balanced composition, exhibiting high wear resistance, low corrosion rate and elastic modulus values approaching those of human bone. Weibull analysis validated the consistency and reliability of key performance metrics. The results show that adding B₄C can change the properties of biomedical alloys, offering engineering advantages for B₄C-reinforced biomedical implants. Ti-B₄C composites exhibit considerable potential for application in advanced implant technologies. Full article

The anodic stability of tungsten carbide (WC) and iron oxide with a spinel structure (Fe₃O₄) were compared against similar data for nanostructured, boron-doped diamond (BDD), and the benchmark Vulcan XC72 carbon, in view of their eventual application as alternative supports for the anion exchange membrane electrolyzer anode. To this end, metal oxide composites were prepared by the in situ autocombustion (ISAC) method, and the anodic behavior of materials (composites as well as supports alone) was investigated in 1 M NaOH electrolyte by the rotating ring–disc electrode method, which enables the separation oxygen evolution reaction and materials’ degradation currents. Among all supports, BDD has proven to be the most stable, while Vulcan XC72 is the least stable under the anodic polarization, with Fe₃O₄ and WC demonstrating intermediate behavior. The Co₃O₄-BDD, -Fe₃O₄, -WC, and -Vulcan composites prepared by the ISAC method were then tested as catalysts of the oxygen evolution reaction. The Co₃O₄-BDD and Co₃O₄-Fe₃O₄ composites appear to be competitive electrocatalysts for the OER in alkaline medium, showing activity comparable to the literature and higher support stability towards oxidation, either in cyclic voltammetry or chronoamperometry stability tests. On the contrary, WC- and Vulcan-based composites are prone to degradation. Full article

Boron carbide (B4C) is a widely recognized ceramic prized for its remarkable properties, including exceptional hardness, low density, and excellent chemical and mechanical stability. To date, limited research has explored the possible health risks associated with B4C nanoparticles (B4C-NPs). This study utilized a Caenorhabditis elegans (C. elegans) in vivo model to investigate the toxicological effects of B4C-NPs at concentrations of 40, 80, 160, and 320 mg/L. Larval nematodes were subjected to prolonged exposure, and their locomotion (head thrashing and body bending), reproduction (brood size), development (body length), lifespan, and gene expression (linked to oxidative stress, metal detoxification, apoptosis, and neurotransmitter synthesis) were assessed. Regarding survival rates, lethality was significantly increased to 5.41% at 320 mg/L of B4C-NPs and lifespan was significantly shortened across all concentrations compared with the controls. Development and reproduction showed slight reductions between 40 and 320 mg/L, while locomotion was markedly impaired at the doses from 80 to 320 mg/L. Gene expression related to antioxidants, apoptosis, cell cycle arrest, neurotransmitter synthesis, and metal detoxification rose significantly at 160–320 mg/L in C. elegans, suggesting that B4C-NPs may induce reproductive and neurological toxicity, delay development, reduce lifespan, and potentially cause genotoxicity in C. elegans. Full article

4H-silicon carbide (4H-SiC) is a cornerstone for next-generation optoelectronic and power devices owing to its unparalleled thermal, electrical, and optical properties. However, its chemical inertness and low dopant diffusivity for most dopants have historically impeded effective doping. This study unveils a transformative laser-assisted boron doping technique for n-type 4H-SiC, employing a pulsed Nd:YAG laser (λ = 1064 nm) with a liquid-phase boron precursor. By leveraging a heat-transfer model to optimize laser process parameters, we achieved dopant incorporation while preserving the crystalline integrity of the substrate. A novel optical characterization framework was developed to probe laser-induced alterations in the optical constants—refraction index ($\mathrm{n}$) and attenuation index ($\mathrm{k}$)—across the MIDIR spectrum (λ = 3–5 µm). The optical properties pre- and post-laser doping were measured using Fourier-transform infrared spectrometry, and the corresponding complex refraction indices were extracted by solving a coupled system of nonlinear equations derived from single- and multi-layer absorption models. These models accounted for the angular dependence in the incident beam, enabling a more accurate determination of $\mathrm{n}$ and $\mathrm{k}$ values than conventional normal-incidence methods. Our findings indicate the formation of a boron-acceptor energy level at 0.29 eV above the 4H-SiC valence band, which corresponds to λ = 4.3 µm. This impurity level modulated the optical response of 4H-SiC, revealing a reduction in the refraction index from 2.857 (as-received) to 2.485 (doped) at λ = 4.3 µm. Structural characterization using Raman spectroscopy confirmed the retention of crystalline integrity post-doping, while secondary ion mass spectrometry exhibited a peak boron concentration of 1.29 × 10¹⁹ cm⁻³ and a junction depth of 450 nm. The laser-fabricated p–n junction diode demonstrated a reverse-breakdown voltage of 1668 V. These results validate the efficacy of laser doping in enabling MIDIR tunability through optical modulation and functional device fabrication in 4H-SiC. The absorption models and doping methodology together offer a comprehensive platform for paving the way for transformative advances in optoelectronics and infrared materials engineering. Full article

Rare earth elements (REEs), particularly neodymium (Nd), dysprosium (Dy), and praseodymium (Pr), are critical in the production of neodymium–iron–boron (NdFeB) magnets used in electronic devices, wind turbines, and electric vehicles. Due to the limited availability of these metals, their recovery from waste electronic equipment such as hard disk drives (HDDs) offers a promising solution. The aim of this study was to develop a method to grind NdFeB magnets obtained from the physical recycling of HDD. The recycled magnets were ground using a planetary mill. A review of the literature highlights the limitations of the currently used grinding methods, which require energy-intensive pretreatment processes, specialised conditions, or expensive equipment. This study employed a Fritsch planetary mill, tungsten carbide grinding balls, and ethanol as a grinding medium. NdFeB magnet samples (120 g) were ground for different durations (0.5 h–15 h) at a speed of 300 rpm, using a cyclic operating mode to minimise material heating. The resulting powders were analysed using a laser particle analyser, an optical microscope, and an X-ray diffractometer. The results enable the determination of optimal grinding parameters, achieving an average particle size (d₅₀) below 5 μm, which is essential for further processing and new magnet production. Finally, the economic and environmental aspects of producing the neodymium alloy were analysed. Full article

This study elucidates the dynamic tribo-mechanical response of laser-cladded FeNiCr-B₄C metal matrix composite (MMC) coatings on AISI 1040 steel substrate, unraveling the intricate interplay between microstructural features and phase transformations. A multi-faceted approach, employing high-resolution scanning electron microscopy (SEM) and advanced X-ray diffraction/Raman spectroscopy techniques, provided a comprehensive characterization of the coatings’ behavior under mechanical and scratch testing, shedding light on the mechanisms governing their wear resistance. Specifically, microstructural analysis revealed uniform coatings with a columnar structure and controlled defect density, showcasing an average thickness of 250 ± 20 μm and a transition zone of 80 ± 10 μm. X-ray diffraction and Raman spectroscopy confirmed the presence of α-Fe (Im-3m), γ-FeNiCr (Fm-3m), Fe₂B (I-42m), and B₄C (R-3m) phases, highlighting the successful incorporation of B₄C reinforcement. The addition of 5 and 7 wt.% B₄C significantly increased microhardness, showing enhancements up to 201% compared to the B₄C-free FeNiCr coating and up to 351% relative to the AISI 1040 steel substrate, respectively. Boron carbide addition promoted a synergistic strengthening effect between the in situ formed Fe₂B and the retained B₄C phases. Furthermore, scratch test analysis clarified improved wear resistance, excellent adhesion, and a tailored hardness gradient. These findings demonstrated that optimized short-pulsed laser cladding, combined with moderate B₄C reinforcement, is a promising route for creating robust, high-strength FeNiCr-B₄C MMC coatings suitable for demanding engineering applications. Full article

Thermal protection materials with excellent performance are critical for hypersonic vehicles. Carbon fiber/phenolic resin composites (C_f/Ph) have been widely used as thermal protection materials due to their high specific strength and ease of processing. However, oxidative failure limits the extensive applications of C_f/Ph in harsh environments. In this paper, a novel hafnium carbide (HfC) and boron carbide (B₄C)-modified C_f/Ph was fabricated via an impregnating and compression molding route. The synergistic effect of HfC and B₄C on the thermal stability, flexural strength, microstructure, and phase evolution of the ceramizable composite was studied. The resulting ceramizable composites exhibited excellent resistance to oxidative corrosion and ablation behavior. The residual yield at 1400 °C and the flexural strength after heat treatment at 1600 °C for 20 min were 46% and 54.65 MPa, respectively, with an increase of 79.59% in flexural strength compared to that of the composites without ceramizable fillers. The linear ablation rate (LAR) and mass ablation rate (MAR) under a heat flux density of 4.2 MW/m² for the 20 s were as low as −8.33 × 10⁻³ mm/s and 3.08 × 10⁻² g/s. The ablation mechanism was further revealed. A dense B–C–N–O–Hf ceramic layer was constructed in situ as an efficient thermal protection barrier, significantly reducing the corrosion of the carbon fibers. Full article

The wear loss and frictional characteristics of magnesium-based hybrid composites reinforced with boron carbide (B₄C) particles and graphite filler were the main subjects of the investigation. Key parameters, including reinforcement content (0–10 wt%), applied load (5–30 N), sliding speed (0.5–3 m/s), and sliding distance (500–3000 m), were varied. Data-driven machine learning (ML) algorithms were utilized to identify complex patterns and predict relationships between input variables and output responses. Five distinct machine learning algorithms, Artificial Neural Network (ANN), Random Forest (RF), K-Nearest Neighbor (KNN), Gradient Boosting Machine (GBM), and Support Vector Machine (SVM), were employed to analyze experimental tribological data for predicting wear loss and coefficients of friction (COFs). The performance evaluation showed that ML models effectively predicted friction behavior and wear behavior of magnesium-based hybrid composites using tribological test data. A comparison of model performances revealed that the Gradient Boosting Machine (GBM) provided superior accuracy compared to other machine learning models in predicting both wear loss and the coefficient of friction. Additionally, feature importance analysis indicated that the graphite weight percentage was the most significant influence in predicting the coefficient of friction and wear loss characteristics. Full article

The purpose of this article is to evaluate and compare the mechanical and electrochemical properties of four new materials, composed of a B₄C ceramic matrix doped with 0.5%, 1%, 2% and 3% volumes of CoCrFeNiMo HEA with monolithic B₄C. The studied samples were obtained using the spark plasma sintering technique. The structure and hardness of the samples were analyzed via scanning electron microscopy (SEM) and a Vickers microhardness test. After immersion in artificial sea water to simulate a corrosive marine environment, corrosion potential, corrosion rate and electrochemical impedance spectroscopy tests were carried out to determine the samples’ electrochemical behavior. Tafel slopes and the equivalent circuit that fit the EIS experimental data were obtained. A denser microstructure and smaller grain size was achieved as the HEA content increase. According to the Vickers measurements, every sample showed a normal distribution. All studied samples exhibit great corrosion resistance in a two-step chemical interaction, influenced by the presence of the Warburg element. The research demonstrates that increasing the HEA content implies better performance of corrosion resistance and mechanical properties, confirming the materials’ potential use in corrosive environments and harsh mechanical applications. Full article

Wide-bandgap semiconductor betavoltaic batteries have a promising prospect in Micro-Electro-Mechanical Systems for high power density and long working life, but their material selection is still controversial. Specifically, the silicon carbide (SiC) betavoltaic battery was reported to have higher efficiency, although its bandgap is lower than that of gallium nitride (GaN) or diamond, which is inconsistent with general assumptions. In this work, the effects of different semiconductor characteristics on the battery energy conversion process are systematically analyzed to explain this phenomenon, including beta particle energy deposition, electron–hole pair (EHP) creation energy and EHPs collection efficiency. Device efficiencies of the betavoltaic battery using SiC, GaN, diamond, gallium oxide (Ga₂O₃), aluminum nitride (AlN) and boron nitride (BN) are compared to determine the optimum semiconductor. Results show that SiC for the betavoltaic battery has higher efficiency than GaN, Ga₂O₃ and AlN because of higher EHPs collection efficiency, less energy loss and fewer material defects, which is the optimal selection currently. SiC betavoltaic batteries were prepared, with the device efficiency having reached 14.88% under an electron beam, and the device efficiency recorded as 7.31% under an isotope source, which are consistent with the predicted results. This work provides a theoretical and experimental foundation for the material selection of betavoltaic batteries. Full article

Submicron particles are widely used in industrial applications due to their unique physical and mechanical properties that enhance the performance of composite materials. In particular, boron carbide particles are valued for their exceptional hardness and high wear resistance and are especially valuable in protective coatings and aerospace applications. However, these particles can agglomerate, significantly impairing their effectiveness. When this occurs during the development of composite materials, physical and mechanical properties are negatively affected. In this paper, a chemical-free method using a non-destructive, open-system dry mechanical deagglomeration technique is developed, leaving the primary particles unaltered, while breaking up strong adhesions between primary particles resulting from the manufacturing process. This method was tested for the deagglomeration of as-received boron carbide submicron particles, with an average primary particle diameter of d₅₀ = 300 nm, and its effect on particle size distribution is presented. Furthermore, X-ray diffraction and true density measurements were carried out on the raw powder. Submicron particles in the dry and as-received state were poured into an experimental mold without a dispersing agent or a protective atmosphere. Static pressure was applied up to 141 MPa to produce tablets at room temperature, finding that 70 MPa yielded the best results in terms of homogeneity, dispersibility, and reproducibility. In order to break apart the densified pressed tablets, ultrasonication was applied before running particle size measurements in the wet dispersed state. Using a tri-laser diffraction light scattering technique, it was determined that particle size distribution followed a Gaussian curve, indicating that this method is suitable to regain the primary submicron particles with uniform properties. It is also shown that applying ultrasound on the as-received powder alone failed to cause the complete deagglomeration of strongly adhering primary particles. These findings suggest that there is no significant wear on the primary particles and no alteration of their surface chemistry, due to the lack of any chemically supported mechanisms such as the alteration of surface charge or the adsorption of surfactants. Furthermore, as the static pressure exerts an immediate impact on all particles in the mold, there is a clear economical advantage in terms of a shorter processing time over other deagglomeration methods such as high shear mixing. Full article

We investigate the resonant characteristics of planar surfaces and distinct edges of structures with the excitation of phonon-polaritons. We analyze two materials supporting phonon-polariton excitations in the mid-infrared spectrum: silicon carbide, characterized by an almost isotropic dielectric constant, and hexagonal boron nitride, notable for its pronounced anisotropy in a spectral region exhibiting hyperbolic dispersion. We formulate a theoretical framework that accurately captures the excitations of the structure involving phonon-polaritons, predicts the response in scattering-type near-field optical microscopy, and is effective for complex resonant geometries where the locations of hot spots are uncertain. We account for the tapping motion of the probe, perform analysis for different heights of the probe, and demodulate the signal using a fast Fourier transform. Using this Fourier demodulation analysis, we show that light enhancement across the entire apex is the most accurate characteristic for describing the response of all resonant excitations and hot spots. We demonstrate that computing the demodulation orders of light enhancement in the microscope probe accurately predicts its imaging. Full article

The transformation of organochlorine and organic impurities such as CCl₄, C₂H₂Cl₂, C₂HCl₃, C₂Cl₄, C₂H₂Cl₄, CH₄, C₃H₈, C₄H₁₀, and C₆H₆ in the content range of 10⁻²–10⁻⁶ wt.%, as well as BCl₃ impurities at the level of 3 × 10⁻² wt.%, was considered. A method has been developed for removing limiting impurities of carbon and boron during the process of the hydrogen reduction of silicon tetrachloride in a high-frequency arc gas discharge at atmospheric pressure. The thermodynamic and gas-dynamic analyses of the reduction process of silicon tetrachloride in hydrogen plasma, along with the behavior of organochlorine impurities, organic substances, and boron trichloride, was conducted. These analyses suggest that under equilibrium conditions, the conversion reactions of impurities result in the formation of silicon carbide and boron silicide. Potential chemical reactions for the conversion of the studied impurities into silicon carbide and boron silicide have been proposed. A new potential for plasma chemical processes has been identified, enabling the effective purification of chlorosilanes from both limiting and limited impurities. The results demonstrate the possibility of significantly reducing the concentrations of organochlorine and organic impurities, as well as boron trichloride, during the reduction of silicon tetrachloride in hydrogen plasma. The maximum conversion rates achieved included 99% for the organochlorine impurity CCl₄ to silicon carbide, 91% for benzene impurity to silicon carbide, and 86% for boron trichloride to boron silicide. Full article

This study investigated the compressive behavior of 30 vol.% boron carbide (B₄C)/2024 aluminum (Al) composites under quasi-static and dynamic loading at different temperatures. Building on the experimental findings, the Johnson–Cook (JC) model was modified, and a complete failure criterion was proposed. These were validated in Abaqus employing the user subroutine for hardening (VUHARD), which incorporated both the modified JC (MJC) model and the complete failure criterion. Experimental results revealed that strain softening was an important feature of the stress–strain curve. The analysis of mechanisms contributing to yield strength revealed that Taylor and load transfer mechanisms dominated, accounting for 89.6% of the total enhancement. Microstructural analysis identified particle fracture and matrix damage were the primary mechanisms driving material failure. Microcracks mainly propagated through the matrix and interface or directly through the ceramic particles and the matrix. The MJC model demonstrated high accuracy in describing the plastic deformation behavior of the composite, with a mean absolute error (MAE) below 15% under dynamic loading. Further simulation confirmed that finite element analyses using the VUHARD subroutine accurately captured the plastic deformation and crack propagation behaviors of the composite under dynamic loading. This study offers a novel approach to describe the plastic deformation and failure behaviors of ceramic-reinforced aluminum matrix composites under dynamic loading conditions. Full article

This research study aims to evaluate the wear and corrosive behaviour of aluminum 6061 alloy hybrid metal matrix composites after reinforcing them with graphene (0.5, 1 wt.%) and boron carbide (6 wt.%) at varying weight percentages. The hybrid composites were processed through ball milling and powder compaction, followed by a microwave sintering process, and T6 temper heat treatment was carried out to improve the properties. The properties were evaluated and analyzed using FE-SEM, Pin-on-Disc tribometer, surface roughness, salt spray test, and electrochemical tests. The results were evaluated prior to and subsequent to the T6 heat-treatment conditions. The T6 tempered sample S1 (Al6061-0.5% Gr-6% B₄C) exhibits a wear rate of 0.00107 mm³/Nm at 10 N and 0.00127 mm³/Nm at 20 N for 0.5 m/s sliding velocity. When the sliding velocity is 1 m/s, the wear rate is 0.00137 mm³/Nm at 10 N and 0.00187 mm³/Nm at 20 N load conditions. From the Tafel polarization results, the as-fabricated (F) condition demonstrates an Ecorr of −0.789 and an Icorr of 3.592 µA/cm² and a corrosion rate of 0.039 mm/year. Transitioning to the T6 condition further decreases Icorr to 2.514 µA/cm², Ecorr value of −0.814, and the corrosion rate to 0.027 mm/year. The results show that an increase in the addition of graphene wt.% from 0.5 to 1 to the Al 6061 alloy matrix deteriorated the wear and corrosive properties of the hybrid matrix composites. Full article