Search Results (9,102)

In designing accurate constitutive models, it is important to investigate the stability of the response obtained by means of these models to perturbations in operator and input data because the properties of materials at different structural-scale levels and thermomechanical influences are stochastic in nature. In this paper, we present the results of an application of the method developed by the authors to a numerical study of the stability of multilevel models to different perturbations: perturbations of the history of influences, initial condition perturbations, and parametric operator perturbations. We analyze a two-level constitutive model of the alpha-titanium polycrystal with a hexagonal closed packed lattice under different loading modes. The numerical results obtained here indicate that the model is stable to perturbations of any type. For the first time, an analytical justification of the stability of the considered constitutive model by means of the first Lyapunov method is proposed, and thus the impossibility of instability in models with modified viscoplastic Hutchinson relations is proved. Full article

In the field of ultrasonic-assisted micro-forming, in addition to acoustic softening, impact effects also play a significant role, especially in terms of influencing the deformation behavior of surfaces, such as by generating more deformation on surface asperity. In this study, to understand the mechanisms involved in the effect of an impact, ultrasonic-assisted micro-forging tests were conducted on commercially pure copper, pure aluminum, and pure titanium. A method that can measure the increment in the temperature during ultrasonic vibration was developed. As a result, changes in the surface temperature of the material under the impact effect and acoustic softening were measured. It is indicated that, during ultrasonic vibration, the heat generated through acoustic softening is very limited and the main heat increase occurs after the impact effect. Once the impact effect occurs, the surface temperature increases with increasing amplitude. Nevertheless, for materials with different crystal structures, the influences of the impact effect are also different. The surfaces of copper and aluminum soften, creating more surface deformation, but the exact opposite effect is seen on a titanium surface. Observing the evolution of the microstructure on the material surface with EBSD demonstrates that the impact effect on FCC materials can reach deeper below the surface in terms of temperature diffusion compared to titanium. Meanwhile, the impact effect in the case of titanium causes the regeneration of twinning, which is reduced under the influence of the acoustic softening effect, consequently resulting in strain hardening. Full article

The ever-increasing expansion of chemical industries produces a variety of common pollutants, including colors, which become a global and environmental problem. Using a nanocatalyst is one of the effective ways to reduce these organic contaminants. With this in mind, a straightforward and effective method for the production of a novel nanocatalyst based on lignin-derived carbon, titanium dioxide nanoparticles, and Ag particles (TiO₂/C/Ag) is described. The preparation of carbon and Ag particles (in sub-micro and nano size) was carried out by laser ablation in air. The nanocomposite was synthesized using a facile magnetic stirrer of TiO₂, C, and Ag. According to characterization methods, a carbon nanostructure was successfully synthesized through the laser irradiation of lignin. According to scanning electron microscope images, spherical Ag particles were agglomerated over the nanocomposite. The catalytic activities of the TiO₂/C/Ag nanocomposite were tested for the decolorization of methylene blue (MB) and Congo red (CR), employing NaBH₄ in a water-based solution at 25 °C. After adding fresh NaBH₄ to the mixture of nanocomposite and dyes, both UV absorption peaks of MB and CR completely disappeared after 10 s and 4 min, respectively. The catalytic activity of the TiO₂/C/Ag nanocomposite was also examined for the reduction of 4-nitrophenol (4-NP) using a NaBH₄ reducing agent, suggesting the complete reduction of 4-NP to 4-aminophenol (4-AP) after 2.30 min. This shows excellent catalytic behavior of the prepared nanocomposite in the reduction of organic pollutants. Full article

The effective welding of a 6 mm thick TA2 pure titanium medium-thickness plate was achieved by laser–arc hybrid welding (LAHW) with helium–argon mixed shielding gas. Conducted research on the influence of helium–argon mixed shielding gas on plasma and arc characteristics during welding, and its further impact on the microstructure, internal porosity defects, tensile properties, and corrosion resistance of welded joints was explored. The study demonstrated that under the shielding gas with 75% helium, the arc width narrowed significantly from 6.96 mm to 2.61 mm, achieving a 63% reduction, which enhanced the concentration of arc heat flux density. Achieved a well-formed weld with no surface spatter and significantly reduced the internal porosity rate from 3.02% to 0.47%, which is an 84% decrease. Tensile fractures are located in the base material, all exhibiting plastic failure. The corrosion resistance of the welded joint initially increased and then decreased with the increase of helium content in the shielding gas, peaking at 75% helium content. Full article

Hydroxyapatite (HAp) polymer composites have gained significant attention due to their applications in bone regeneration and tooth implants. This review examines the synthesis, properties, and applications of Hap, highlighting various manufacturing methods, including wet, dry, hydrothermal, and sol–gel processes. The properties of HAp are influenced by precursor materials and are commonly obtained from natural calcium-rich sources like eggshells, seashells, and fish scales. Composite materials, such as cellulose–hydroxyapatite and gelatin–hydroxyapatite, exhibit promising strength and biocompatibility for bone and tissue replacement. Metallic implants and scaffolds enhance stability, including well-known titanium-based and stainless steel-based implants and ceramic body implants. Biopolymers, like chitosan and alginate, combined with Hap, offer chemical stability and strength for tissue engineering. Collagen, fibrin, and gelatin play crucial roles in mimicking natural bone composition. Various synthesis methods like sol–gel, hydrothermal, and solution casting produce HAp crystals, with potential applications in bone repair and regeneration. Additionally, the use of biowaste materials, like eggshells and snails or seashells, not only supports sustainable HAp production but also reduces environmental impact. This review emphasizes the significance of understanding the properties of calcium–phosphate (Ca-P) compounds and processing methods for scaffold generation, highlighting novel characteristics and mechanisms of biomaterials in bone healing. Comparative studies of these methods in specific applications underscore the versatility and potential of HAp composites in biomedical engineering. Overall, HAp composites offer promising solutions for improving patient outcomes in bone replacement and tissue engineering and advancing medical practices. Full article

Titanium alloys are crucial in precision manufacturing due to their exceptional properties, but traditional machining methods lead to tool wear, deformation, and high costs. Conventional cooling fluids reduce heat but cause environmental issues, necessitating more sustainable solutions. Cryogenic Minimum Quantity Lubrication (CMQL) technology, using liquid nitrogen or carbon dioxide with minimal amounts of cutting fluid, offers an eco-friendly alternative that reduces machining temperatures and friction. This study tested the TC6 titanium alloy under conventional and CMQL conditions, focusing on tool wear, surface quality, and machining efficiency. Results showed that CMQL significantly decreased tool wear and surface roughness, with a 42% reduction in surface roughness during drilling and a 20–30% efficiency increase. The findings highlight CMQL’s potential to improve machining quality and efficiency while promoting environmentally friendly practices in the industry. Full article

Titanium carbide (TiC) coatings were prepared on the surface of AlFeCoCrNiCu high-entropy alloy blocks using electro-spark deposition (ESD). The microhardness and corrosion resistance of the TiC coatings prepared under different voltage and capacitance process parameters were studied. The research shows that the maximum microhardness of the TiC coating on sample 4 (working voltage of 20 V, working capacitance of 1000 μF) is 844.98 HV, which is 81.5% higher than the microhardness of the substrate. This is because the deposition energy increases with the increase in voltage, and the adhesion and aggregation between the coating and the substrate are enhanced, increasing the hardness of the coating. It is worth noting that excessive deposition energy can increase surface defects and reduce the microhardness of the coating surface. Electrochemical testing analysis shows that the corrosion current density of the TiC coating is the lowest (9.475 × 10⁻⁷ ± 0.06 × 10⁻⁷), and the coating impedance is the highest (2.502 × 10³ Ω·com²). The absolute phase angle value is the highest (about 72°). The above indicates that the TiC coating prepared with a working voltage of 20 V and a working capacitance of 1000 μF has better microhardness and corrosion resistance. Full article

The effective recovery of gallium from wastewater discharge in the Bayer process is promising for the long-term development of gallium resources. The adsorption and desorption behavior of gallium (Ga), vanadium (V), and aluminum (Al) ions on a strong acidic styrene cation exchange resin (JK resin) from a simulated Bayer solution was systematically investigated by static experiments. The results showed that the optimum conditions for separating Ga from V and Al were at low temperatures and short contact times, with 78.30%, 15.16%, and 6.63% of the adsorption efficiency at 25 °C and 60 min, respectively, for Ga, V, and Al. The adsorption kinetics of Ga³⁺ conformed to the pseudo-second order model, and the static saturation adsorption capacity was 18.25 mg/g. The Langmuir model fitted the adsorption isotherm of gallium well, and the maximum adsorption capacity was 1.11 mg/g at 25 °C. FT-IR spectroscopy and XPS showed that the mechanism of the Ga³⁺ adsorption was only related to the interaction of the oxygen atoms of the amide oxime group (C=NOH). The separation of Ga, V, and Al can be achieved by desorbing 98% of Al with low concentrations of ammonia and 90% of Ga with low concentrations of hydrochloric acid. The results indicate that JK resin is an efficient adsorbent for separating gallium and vanadium in alkaline solutions. Full article

Atenolol is a medication belonging to the class of drugs known as beta-blockers, used to treat high blood pressure (hypertension) and irregular heartbeats (arrhythmia). Their presence in the environment has serious impacts on humans, animals, and the water ecosystem. In this context, the aim of this study was to develop a simple voltammetric method for the determination of atenolol (ATN) using carbon paste electrodes modified with the nanomaterials TiO₂ and rGO/TiO₂. The analytical performance of the modified sensor was evaluated using square wave voltammetry and cyclic voltammetry in 0.1 mol L⁻¹ acid sulfuric solution (H₂SO₄), pH 2. The nanocomposite electrode CPE/rGO/TiO₂ exhibited excellent electrocatalytic activity towards ATN oxidations at 0.1 mol L⁻¹ H₂SO₄ compared with unmodified carbon paste electrodes CPEs and those modified with titanium oxide, CPE/TiO₂. Different experimental and conditional parameters were optimized, such as supporting electrolytes, pH, amplitude, frequency, etc. Under optimal conditions, linear calibration curves were obtained, ranging from 1.7 to 23.2 µmol L⁻¹ for ATN with detection limits of 0.05 μmol L⁻¹. The modified nanocomposite CPE/rGO/TiO₂ sensor showed good sensitivity and good repeatability (RSD ≤ 0.61%) for ATN determination. The proposed sensor is mechanically robust and presented reproducible results and a long useful life. In order to verify the usefulness of the developed methods, the nanocomposite sensor CPE/rGO/TiO₂ was applied for the detection of atenolol in real samples (pharmaceutical tablets without any pre-treatment). The excipients present in the tablets did not interfere in the assay. Recoveries ranging from 97.7% to 106% were obtained. The results showed that the CPE/rGO/TiO₂ voltammetric sensor could be successfully applied in the routine quality control of ATN in complex matrices. Full article

We performed a gas nitriding and quenching process (GNQP) on Ti–18 mass% Nb alloy to obtain a high damping capacity and wear resistance. GNQP was performed at temperatures of 1023, 1123, and 1223 K. The outermost surface of the GNQP specimen obtained at 1023 K mainly comprised TiO₂, whereas that at 1223 K mainly comprised TiN. The surface and interior of the specimens exhibited higher hardness at 1223 K than that at 1023 K. Compared to the specimen obtained by solution–quenching (AQ), the unit volume of the α” martensite phase at a depth of 320 μm of the GNQP specimen obtained at 1023 K was similar, and that at 1223 K was higher. Such a difference can be related to the difference in the core hardness of the specimens. The wear amounts of all GNQP specimens were lower than those of the AQ specimen. The coefficient of friction of the GNQP specimen obtained at 1023 K was lower than that obtained at 1223 K. The surface constituent phase and surface roughness exhibited a strong influence on the wear at a load of 500 g. Meanwhile, the nitride layer and damping capacity were considered to be related to the wear at a load of 3000 g. Full article

The Carboniferous-Permian coal measure strata in the Qinshui Basin exhibit highly lithium (Li) enrichment, with substantial exploitation potential. To further explore the enrichment mechanism of lithium in coal measure strata, the No. 15 coal of the Taiyuan Formation from the Gaoping mine is taken as the research object, and its mineralogical and geochemistry characteristics are evaluated using optical microscopy, X-ray diffraction, scanning electron microscopy, inductively coupled plasma mass spectrometry, X-ray fluorescence, and infrared spectral. The results show that the No. 15 coal is semi-anthracite coal with low moisture, low ash, low volatility, and high sulfur. Organic macerals are primarily vitrinite, followed by inertinite, and liptinite is rare; the inorganic macerals (ash) are dominated by clay minerals (predominantly kaolinite, cookeite, illite, and NH₄-illite), calcite, pyrite, quartz, siderite, gypsum, and zircon. The average Li content in the coal is 66.59 μg/g, with higher content in the coal parting (566.00 μg/g) and floor (396.00 μg/g). Lithium in coal occurs primarily in kaolinite, illite, cookeite, and is closely related to titanium-bearing minerals. In addition, Li in organic maceral may occur in liptinite. The No. 15 coal was formed in the coastal depositional system, and the deposition palaeoenvironment is primarily a wet–shallow water covered environment in open swamp facies; the plant tissue preservation index is poor, and aquatic or herbaceous plants dominate the plant type. The reducing environment with more terrestrial detritus, an arid climate, and strong hydrodynamic effects is favorable for Li enrichment in coal. The results have important theoretical significance for exploring the enrichment and metallogenic mechanisms of Li in coal. Full article

The functionality of the NiTi shape memory alloy was improved through engineering Ag-SiO₂-TiO₂ nanocomposite coatings. For this purpose, an anaphoretic deposition process, conducted at a constant voltage of 40 V and deposition times ranging from 1 to 10 min, was used. Scanning electron microscopy (SEM) analysis demonstrated that the deposition parameters significantly impacted the morphology of the coatings. Complementary Raman Spectroscopy and X-ray diffraction (XRD) analyses confirmed the successful formation of distinct nanocomposite layers, and revealed the details of their crystalline structure and chemical composition. After that, the adhesion between the NiTi substrate and the electrophoretically deposited ceramic coatings was improved through a post-deposition heat treatment. To prevent excessive shrinkage and cracking of the coating, tests were carried out to characterize the behavior of the coating material at elevated temperatures. The nanocomposite coatings were exposed to a temperature of 800 °C for 2 h. The annealing induced significant structural and morphological transformations, resulting in layers that were distinctly different from both the original materials and those produced solely through electrophoretic deposition. The thermal treatment resulted in the formation of a new kind of nanocomposite structure with enhanced reactivity. Full article

The long-term safety of pressure-resistant structures used in deep-sea equipment may be threatened by creep deformation. The creep deformation behavior of a pressure-resistant structure made of different titanium alloys, Ti-6Al-4V and Ti-4Al-2V, at room temperature is investigated in this research. The kinetics and mechanisms underlying creep deformation in these materials is explained by proposing an improved constitutive model considering the effects of stress level, loading rate and environmental temperature field, offering crucial information for optimizing design parameters and guaranteeing the lifespan of the structure. Model parameters are determined for the two types of titanium alloys based on tensile creep testing results and validated through a simulation of the experimental process. In this study, a material creep model was used to predict the long-term deformation of large pressure-resistant titanium structures to ensure safe long-term operation. The safety factor used in the model is 1.5. Finite element analyses are conducted for the creep behavior of the pressure-resistant structure under real operating circumstances based on the creep constitutive model. The simulation predicts stress distribution, strain evolution, and deformation size over long periods of time by integrating complicated geometries, boundary conditions, and material characteristics. The present research can provide basic information for the local impacts of creep deformation on the inside of facilities, which helps refine design strategies to reduce possible damage risks. Full article

This study examines the efficacy of icephobic polyurethane nanocomposite coatings in mitigating corrosion on an aluminum substrate. A titanium-based conversion coating is applied to modify the substrate, and the research focuses on optimizing the dual functionalities of icephobicity and anticorrosion within the polyurethane coatings while ensuring strong substrate adhesion. The coatings are formulated using fluoropolyol, isocyanate, and silica nanoparticles treated with polydimethylsiloxane. Surface properties are analyzed using contact angles, contact angle hysteresis measurements, and atomic force microscopy, and the coatings’ icephobicity is evaluated through differential scanning calorimetry, freezing time delay, ice adhesion under impact and non-impact conditions, and ice accretion tests. The corrosion resistance and adhesive strength of the coatings are assessed using electrochemical impedance spectroscopy and cross-cut tests, respectively. Increasing the concentration of silica nanoparticles to 10 wt.% increases contact angles to 167°, although the 4 wt.% coating produces the lowest contact angle hysteresis (3° ± 0.5°) and ice nucleation temperature (−23 °C). The latter coating is then applied to a substrate pretreated with a titanium/cerium-based conversion coating. This prepared surface maintains an ice adhesion of about 15 kPa after 15 icing/de-icing cycles and provides approximately 90 days of surface protection (|Z|_lf = 1.6 × 10⁹ Ω·cm²). Notably, the impedance value exceeds that of untreated substrates, underscoring the effectiveness of the titanium/cerium-based conversion coating in enhancing both corrosion resistance and coating adhesion to the substrate. Full article

TC4 ELI alloy is widely used in the marine, medicine, and aviation fields. The failure performance of TC4 ELI alloy is significantly different from that of other metal materials, such as steels. In this paper, a modified Mohr–Coulomb criterion is calibrated based on several kinds of specimens under different stress states and a 3D geometric representation of a modified Mohr–Coulomb fracture locus for TC4 ELI is obtained based on these parameters. The effectiveness of the modified M-C criterion is studied by a ring-stiffened cylinder made of TC4 ELI. The ultimate strength of the cylinder obtained in the simulation with the modified M-C criterion is close to that obtained in an external pressure experiment, which shows that the modified M-C criterion is suitable for predicting failure in pressure hulls made of titanium alloy used in the deep-sea field. Full article