Search Results (255)

Ceramic balls are utilized as grinding media for regrinding of titanomagnetite rougher, owing to its low liberation degree and intricate intergrowth with gangue minerals. Process mineralogy, regrinding experiments and EDEM simulations were adopted to investigate the influencing mechanism of ceramic balls on the regrinding performance of titanomagnetite rougher. The Dv(90) of titanomagnetite rougher is 198.19 μm, and the titanomagnetite is closely intergrown with gangue minerals, including chlorite, serpentine and ilmenite, in the forms of inclusions, interlocks and solid solutions with a liberation degree of 75.54%. The Dv(90) reduces to 39.86 μm, and the liberation degree of titanomagnetite increases to 92.86% after regrinding with ceramic balls. The grade was improved from 53.01% to 58.83% with a recovery of 96.19% after magnetic separation. EDEM simulation results reveal that raising stirrer speed elevated collision energy, increasing pulp density enhanced viscous coupling and particle capture, and improving media filling ratio boosted collision frequency. These findings demonstrate that ceramic balls could effectively refine product size, facilitate mineral liberation and improve concentrate grade, offering a viable pathway toward efficient utilization of titanomagnetite. Full article

This study presents an initial effort to develop Low-Temperature Cofired Ceramics (LTCC) using local bio-sourced materials: Saint Jacques shells and slate tiles. Chemical analysis confirms that the Saint Jacques shells provide CaO and CaCO₃, while slate supplies the needed SiO₂ and Al₂O₃. The constituents, processed from a formulation targeting 70 wt% slate and 20 wt% shell fragments are crushed and ball-milled, mixed with 10 wt% boron trioxide (B₂O₃), and calcinated at 700 °C for two hours to remove organics, followed by a second milling. An aqueous slurry is then prepared and manually tape-cast to form tapes that are processed through standard LTCC process steps. Initial green-state mechanical tests showed elongation values up to ~7.8% and tensile break forces in the range of ~0.5–1.0 N, with lamination performed successfully using standard isostatic conditions. Cofiring yielded limited lateral shrinkage (~6%) but substantial vertical shrinkage (27%). Two-line method measurements indicate a relative permittivity of approximately 4.3 with a comparatively high loss tangent of 0.03, suggesting a vitreous phase and/or porous, inhomogeneous microstructure. A final resonator prototype is fabricated, yielding somewhat encouraging results for the feasibility of this bio-sourced LTCC route while highlighting the need to reduce dielectric losses in future work. Full article

During the operation of full-ceramic bearings, defects such as cracks and spalls inevitably develop on the bearing balls. These defects reduce bearing service life and compromise the stable operation of mechanical systems. To address this issue, a 12-degree-of-freedom (DOF) dynamic model of a full-ceramic bearing-rotor system (BRS) is established, considering ball crack and spalling defects. The model incorporates variations in equivalent stiffness and contact forces induced by these two defect types. Subsequently, the proposed model is solved by the Newmark–β method. Bifurcation diagrams, time-domain waveforms, and frequency spectra are employed to investigate the system’s dynamic responses. In the frequency-domain analysis, particular attention is paid to characteristic frequency components, including the rotational frequency f_s, the ball spin frequency f_BSF, their harmonics, and combination frequencies. Finally, an experimental test platform is constructed to validate the accuracy of the developed model. The results indicate that crack and spalling defects exert distinctly different effects on the dynamic behavior of the system. Defect width has a significant quantitative influence on the vibration response. Under various defect conditions, the prediction errors of the developed model remain within an acceptable range, with the maximum relative error of 9.05%. The developed model offers a theoretical foundation for analyzing bearing dynamics and supporting fault diagnosis applications. Full article

Rubber aggregate concrete (RAC) offers excellent frost resistance and impact toughness, but the incorporation of rubber particles substantially reduces its compressive strength, limiting structural applications. Existing improvement strategies have mainly relied on a single modification route, whereas the dynamic compressive response of RAC containing both ceramic balls and steel fibers remains insufficiently clarified. Here, a ceramic ball–steel fiber rubber aggregate concrete (CBSFRC) was investigated using quasi-static compression, a Φ120 mm split Hopkinson pressure bar system, and high-speed photography. Three steel-fiber volume fractions (1.0%, 1.5%, and 2.0%) were tested. The CBSFRC waveform displayed a characteristic ‘low-first, high-second’ double-peak pattern, in contrast to the ‘high-first, low-second’ pattern of the reference rubber aggregate concrete (CRC). At the common interpolated strain rates of 40, 45, and 50 s⁻¹, the dynamic compressive strengths of CBSFRC were 35.9–53.6% higher than those of CRC; no extrapolation was used. The largest quasi-static strength increase among the tested mixtures was 51.7%. The observed CBSFRC ultimate strains and strain energy densities ranged from 11.1–17.5 × 10⁻³ to 8.1–14.1 × 10⁵ J/m³, respectively. Matched-rate analysis showed that the largest DIF increment was 18.8% for SF-1CBRC at 40 s⁻¹, whereas the largest strain-energy-density increment was 70.2% for SF-1.5CBRC at 50 s⁻¹. These results describe the tested range and do not establish a universal optimum steel-fiber content. Full article

Wet grinding is an important operation in the technological process of ceramic tile production. The properties of the slurry obtained from grinding (slip) are conditioned by the raw materials (the type and characteristics of raw material in mixture, recipes for mixture), and by the operating parameters in grinding (technical characteristics of mill, type of grinding system, mill charge, grinding media body, grinding time, etc.). The optimal selection of these influential parameters results in satisfactory properties of slip, i.e., in efficient grinding as process operation, and, consequently, in smooth and efficient realisation of subsequent operations in the process, particularly spray drying. At the end of the technological process, the final goal is to obtain a ceramic tile of satisfactory quality. Multi-criteria decision-making (MCDM) is an increasingly applied tool for selecting optimal technological parameters for the purpose of optimisation, problem solving and improvement of technological processes. This paper presents the application of the symmetry point of criterion—ranking alternatives by perimeter similarity (SPC-RAPS) as an MCDM hybrid method for the selection of optimal technological parameters in grinding in the ceramic tile production process. The ranking and selection of alternatives (raw materials, grinding balls and grinding time) were performed according to various criteria. In addition to the technological parameters related to the characteristics of the products from the grinding (slip), and to the technical characteristics of the final product (ceramic tiles), the criteria also included economic parameters (the market price of raw material and specific energy consumption in grinding). The developed mathematical model enabled the selection of the best alternative as a solution for this problem. Full article

Bearings are essential components in mechanical systems, with ceramic ball bearings increasingly adopted in turbine, automotive, and aerospace applications due to their superior strength and durability. Despite these advantages, bearings are subjected to significant cyclic loading, which can accelerate plastic deformation and lead to sudden catastrophic failure. Current approaches for predicting bearing lifespan rely on time-consuming theoretical and experimental methods. This study proposes a more efficient finite element (FE) approach to predict fatigue behaviour in silicon nitride ball bearings operating under lubricated conditions. In this research, a 12.7 mm diameter silicon nitride ball bearing was analysed under a Hertzian contact pressure of 3 GPa using SolidWorks Simulation 2023 (SWS). Friction coefficients ranging from 0.00 to 1.00 were investigated to represent different lubrication conditions. The results indicate that the stress amplitude remained below the fatigue limit of 1.02 GPa for friction coefficients up to 0.80, while fatigue failure was predicted at a coefficient of 1.00, corresponding to 1.086 × 10⁴ cycles. Full article

The synergistic co-production of ceramic fibers from fly ash and coal gangue offers a promising path for their high-value utilization. However, research in this area remains limited, hindering its broader application. This study employs numerical simulations to assess the influence of high-wheel rotational speed and melt temperature on the mass of inter-wheel melt transfer, as well as their effects on ligament size and slag-ball fraction. The results show that the high wheel, responsible for melt pre-fragmentation and transfer, plays a crucial role in determining the mass of inter-wheel melt transfer and controlling ligament dimensions. In contrast, the low wheel does not directly affect ligament size but aids in transforming pre-fragmented droplets into ligaments and modulates their dispersion. Melt temperature impacts both transfer mass and ligament size by modifying melt properties. The slag-ball fraction increases with the melt temperature and decreases with the high-wheel speed, while the low-wheel speed has a negligible effect. Under the optimal operating conditions of a melt temperature of 1745 °C and equal rotational speeds of 10,000 rpm for both the high and low wheels, a ligament structure with a relatively concentrated size distribution is obtained, with the slag-ball fraction effectively controlled within the range of 8–13%. Full article

Copper and its alloys are widely used in electrical, automotive, aerospace, and energy applications because of their excellent thermal and electrical conductivity. However, the low hardness and poor wear resistance of pure Cu limit its use under tribologically demanding sliding conditions. In this study, Cu matrix composites reinforced with 1 wt.% boron carbide (B₄C), boron (B), chromium (Cr), cobalt (Co), alumina (Al₂O₃), and graphite (Gr) were fabricated by powder metallurgy and comparatively evaluated under identical processing and testing conditions. Phase constitution and microstructural characteristics were analyzed by XRD, SEM, and EDS, while mechanical and tribological behavior was assessed by Vickers hardness and dry sliding wear tests. All reinforcements improved the hardness of the Cu matrix compared with unreinforced Cu. The hardness increase followed the order Cu–B₄C (68.91%) > Cu–B (66.43%) > Cu–Gr (63.97%) > Cu–Al₂O₃ (61.79%) > Cu–Cr (42.69%) > Cu–Co (36.04%). Dry sliding wear tests, performed under a 10 N normal load, 0.05 m s⁻¹ sliding speed, and 1000 m sliding distance against a 316L stainless-steel ball, showed that all reinforced composites exhibited lower mass loss and more stable sliding behavior than pure Cu. Among all samples, Cu–B₄C displayed the best wear performance, with a 154.8% improvement in wear resistance relative to pure Cu. SEM analysis of the worn surfaces revealed that reinforcement addition reduced severe plastic deformation, groove formation, and delamination, leading to a more stable wear regime. Graphite- and boron-containing composites benefited from interfacial lubrication and contact stabilization, whereas B₄C and Al₂O₃ improved wear resistance through rigid-particle strengthening and enhanced load-bearing capacity. By comparing ceramic, metalloid, metallic, oxide, and solid-lubricating reinforcements at the same low addition level and under identical processing and testing conditions, this study provides a reinforcement-selection framework for Cu-based composites requiring improved hardness and dry-sliding durability. Full article

In hybrid rolling bearings operating under extreme high-temperature and high-load conditions, steel rolling elements are prone to early failure, which has accelerated the widespread adoption of ceramic materials. To address the limitations of conventional studies, which have focused mainly on macroscopic wear parameters while neglecting subsurface failure mechanisms and the relationship among sintering process, microstructure, and fatigue performance, this work systematically compares the tribological behavior of Si₃N₄ ceramic balls fabricated by high-pressure electric resistance hot-pressing (REHP) and B₄C ceramic balls prepared by conventional hot pressing (HP) against 52100 steel counterparts. The central innovation of this study lies in clarifying, based on Hertzian contact theory and Lundberg-Palmgren life theory, that subsurface orthogonal shear stress, rather than surface compressive stress, is the fundamental driving force for contact fatigue failure of ceramic balls. In addition, two distinct damage evolution modes are revealed: B₄C exhibits early-stage brittle fracture and large-scale spalling, whereas REHP-Si₃N₄ is characterized by microcrack initiation and slow crack propagation. Moreover, the intrinsic mechanism by which the REHP process significantly enhances the contact fatigue life of ceramics is elucidated; namely, it refines grain size, eliminates residual porosity, and increases densification. The results show that, under the same high-load conditions, the mass loss of REHP-Si₃N₄ ceramic balls is only 35.7% of that of HP-B₄C, while the service life is extended by 20%. This work provides a key theoretical basis for ceramic material selection and sintering process optimization in high-performance hybrid bearings. Full article

Non-stoichiometric high-entropy carbides (Nb_0.2Ta_0.2Ti_0.2W_0.2Zr_0.2)C_x (x = 0.71–0.85) nanoscale powders were prepared using oxides and carbon as raw materials via carbothermal reduction. The (Nb_0.2Ta_0.2Ti_0.2W_0.2Zr_0.2)C_0.73 synthesized at 1700 °C exhibited a grain size of approximately 400 nm, an oxygen content of 0.3 wt.%, and uniform nanoscale distribution of the five metal elements. After ball milling, (Nb_0.2Ta_0.2Ti_0.2W_0.2Zr_0.2)C_0.73 powder was sintered by spark plasma sintering to produce high-entropy ceramics with a relative density of 98.1% and an average particle size of about 5.3 μm. The Vickers hardness, nano-hardness, Young’s modulus, and fracture toughness were 17.6 GPa, 29.1 GPa, 514 GPa, and 5.3 MPa·m^1/2, respectively. The thermal conductivity of the ceramic at room-temperature was as low as 8.5 W/m·K. Full article

This study prepares three types of Si₃N₄ ceramic bearing balls with distinct microstructures by regulating the content of Al₂O₃-Y₂O₃ sintering aids, and systematically investigates the influence mechanisms of microstructure, grain boundary phase distribution and grain aspect ratio on the rolling contact fatigue (RCF) failure behavior. The experimental results show that a low content of sintering aids leads to insufficient liquid phase formation, hindered densification and porous defects inside the material, with spalling as the dominant RCF failure mode and the Weibull modulus being only 1.877. With the increase in sintering aid content, the liquid phase promotes densification and the growth of elongated β-Si₃N₄ grains; when the average grain aspect ratio reaches 4.47, the grain toughening mechanism significantly improves the RCF life, with the characteristic life attaining 1.035 × 10⁷ cycles. However, an excessive content of sintering aids induces the steric hindrance effect, which inhibits grain growth and increases the content of soft grain boundary phases, thus leading to the transition of the failure mode to wear and a subsequent decrease in service life. This study demonstrates that an appropriate liquid phase content is crucial for balancing the densification degree, grain morphology and RCF performance of Si₃N₄ ceramic bearing balls. Full article

This study focuses on China’s domestically developed K452 alloy. Using Si₃N₄ ceramic balls as the counterface material, the tribological properties of the K452 alloy were investigated after heat treatment over a wide temperature range (RT–800 °C), and the wear mechanisms were analyzed. The results show that the heat treatment process enhances the material hardness slightly by promoting the dissolution of the γ′-strengthening phase and the precipitation of the η phase. From RT to 600 °C, the wear rate of the K452 alloy remains at a relatively low level, on the order of 10⁻⁶ mm³·m⁻¹·N⁻¹. Compared with the as-cast condition, intermediate treatment exhibits a significant reduction in the wear rate. Compared with traditional processes, it reduces one step of heat treatment. This improvement is attributed to the precipitation of the uniformly fine η phase, along with the re-dissolution of the γ′-strengthening phase. When the testing temperature is raised to 800 °C, the tribological performance of the K452 alloy deteriorates significantly, with the wear rate increasing to the order of 10⁻⁵ mm³·m⁻¹·N⁻¹. Microstructural characterization confirms that the in situ formations of dense Cr₂O₃ and Al₂O₃ oxide films during friction are the primary mechanism for improved wear resistance from RT to 600 °C. But when the temperature rises to 800 °C, the dynamic equilibrium of the oxide layers is disrupted, leading to oxidative wear becoming the dominant mechanism. Full article

The structural response of ceramics to extreme deformation is of significant scientific and technological relevance since such conditions are commonly encountered during both processing and service. In this study, monoclinic zirconia was subjected to high-energy ball milling for extended durations of 80 h and 120 h, followed by annealing at 1000 °C. X-ray diffraction revealed a progressive increase in the tetragonal phase content with milling duration, while subsequent annealing promoted its consolidation alongside the principal monoclinic phase, resulting in a stable biphasic structure. The phase evolution is also evaluated through a Raman spectroscopy analysis and correlated with the morphology, mechanical properties, and surface area analyses. Scanning electron microscopy confirmed the preservation of nanoscale features in the milled and annealed specimens, in contrast to the unmilled sample, which exhibited pronounced grain coarsening. The combined presence of nanostructural stability and biphasic phase constitution underscores the efficacy of high-energy ball milling, in conjunction with thermal treatment, as an effective strategy to tailor the microstructure and phase stability of zirconia ceramics for advanced engineering applications. Full article

To address the increasing demands for lightweight, high-temperature resistant braking materials under extreme service conditions, a novel C_f/SiC-B₁₂(C,Si,B)₃ composite was developed in this work. The composite was fabricated via a hybrid slurry infiltration-reactive melt infiltration (SI-RMI) process. The tribological performance under coupled temperature–velocity conditions was systematically evaluated using a ball-on-disk tester over temperatures from 25 to 600 °C (at 900 r/min) and sliding speeds from 300 to 900 r/min (at 600 °C). The results indicate that temperature dominates the friction and wear behavior. At room temperature, the composite exhibits a friction coefficient of 0.52 and a wear rate of 4.019 × 10⁻⁴ mm³/(N·m). With increasing temperature, friction coefficients decreased to 0.43 at 400 °C and 0.41 at 600 °C, while wear rates increased sharply to 12.025 × 10⁻⁴ mm³/(N·m) at 400 °C before declining to 5.228 × 10⁻⁴ mm³/(N·m) at 600 °C. Under the fixed temperature of 600 °C, raising rotational speed from 300 to 900 r/min increased the wear rate only marginally (4.953 to 5.228 × 10⁻⁴ mm³/(N·m)). Surface analysis indicates that a continuous Si-B-O oxide layer (mainly SiO₂ and B₂O₃) forms at 600 °C, which may provide solid lubrication and oxidation resistance. The present work offers a preliminary exploration of the tribological evolution and self-lubrication mechanisms of C_f/SiC-B₁₂(C,Si,B)₃ composites, providing potential insights for the design of advanced ceramic-matrix braking materials. Full article

Multilayer zirconias have recently been introduced as dental biomaterials to combine improved translucency with sufficient mechanical reliability by implementing yttria-driven gradients in phase composition. Such materials can be considered functionally graded ceramics, where local phase stabilization influences strength and crack resistance. However, manufacturer-specific gradient profiles and their structure–property relationships remain insufficiently characterized. This study investigated two commercially available multilayer zirconias with distinct gradient concepts: IPS e.max^® ZirCAD Prime (continuous gradient) and KATANA™ Zirconia YML (stepwise gradient). Ten equidistant sections along the blank height were analyzed using quantitative X-ray diffraction and Rietveld refinement to quantify zirconia phase fractions and estimate local Y₂O₃ content. Mechanical behavior was evaluated by biaxial flexural strength testing (ball-on-three-balls method) and fracture toughness testing using the chevron-notched beam technique. Both materials exhibited pronounced yttria- and phase-dependent gradients consistent with their reported layer designs. Regions with increased yttria content showed higher t″ fractions and reduced fracture toughness and strength, whereas deeper regions displayed increased mechanical performance associated with higher fractions of transformable tetragonal phase. These findings emphasize that multilayer zirconias exhibit spatially dependent mechanical properties, which should be considered in biomaterial selection and restoration design, particularly when balancing aesthetic demands and fracture resistance. Full article