Search Results (311)

Ultra-high-temperature ceramic (UHTC) coatings offer a promising route to extending cutting tool service life under severe conditions. This work evaluates the tribological behaviour and wear regime transitions of ZrB₂–SiC/ZrO₂ coatings, deposited by physical vapour deposition (PVD) onto ASSAB-17 high-speed steel tool bits, during dry turning of Ti-6Al-4V. Structural, microstructural, mechanical, and tribological characterisation was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), nanoindentation, and pin-on-disc testing under three pressure–velocity (PV) severity levels, with worn surfaces analysed by SEM and profilometry. The coating exhibited a nanostructured ZrB₂/β-SiC/t-ZrO₂ architecture with a hardness (H) of 24 ± 3 GPa, a hardness-to-reduced-elastic-modulus ratio (H/Er) of 0.100, and an elastic resistance to plastic deformation (H³/Er²) of 0.240 GPa. Three tribological regimes were identified: running-in, steady-state sliding, and progressive degradation, with the highest severity (PV = 6.0 N·m/s) triggering degradation beyond approximately 620 m, a more than one-order-of-magnitude rise in wear rate, and the only case exceeding the tool-life criterion of maximum flank wear (VBmax = 0.30 mm) according to ISO 3685. The main advantage of the proposed approach is that it condenses tool-life-relevant behaviour into a single, easily measurable severity parameter, the PV product, directly applicable to coating design and the selection of safe machining-condition windows. The overall behaviour is consistent with a mechanism governed by the stability and regeneration capacity of a protective tribofilm. As the composition of this layer was not directly characterised, this mechanism is proposed as a phenomenological interpretation, from which a PV threshold is derived as a design criterion for UHTC coatings. Full article

Silicon nitride (Si₃N₄) is an advanced structural ceramic with considerable potential for load-bearing biomedical applications owing to its excellent mechanical properties and favorable biological response. In this study, the effect of wollastonite (CaSiO₃) addition on the microstructure, mechanical performance, and in vitro bioactivity of Si₃N₄–CaSiO₃ ceramic composites was investigated. Composites containing 5–30 wt.% wollastonite were prepared by pressureless sintering at 1800 °C for 1 h and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), density measurements, nanoindentation, Vickers hardness, fracture toughness, compressive strength, and simulated body fluid (SBF) immersion tests. Increasing the wollastonite resulted in progressive densification up to 20 wt.% CaSiO₃, resulting in a maximum relative density of 96%, together with complete α→β-Si₃N₄ transformation and the development of elongated β-Si₃N₄ grains. The composition containing 20 wt.% wollastonite exhibited optimum mechanical performance, achieving a hardness of approximately 13 GPa, fracture toughness of ~5.5 MPa·m^1/2, and compressive strength of ~2840 MPa. The results demonstrate that wollastonite plays a multifunctional role in Si₃N₄ ceramic composites by promoting densification during sintering and improving in vitro bioactivity while maintaining high mechanical performance. These findings highlight the potential of Si₃N₄–CaSiO₃ ceramic composites as promising bioactive structural materials for load-bearing orthopedic and dental applications. Full article

The development of sustainable, high-performance friction composites is critical for the automotive industry, given the environmental and health concerns associated with conventional brake pad materials such as asbestos and copper. This study investigates the effect of incorporating micro- and nano-sized Al₂O₃, SiC, and carbon nanotubes (CNTs) into a novel, eco-friendly, asbestos-free, and copper-free brake pad formulation. Six composite samples were fabricated via a cold-pressing and hot-molding process: five formulations containing a single, size-controlled micro-/nano-sized reinforcement (Al₂O₃, SiC, and CNTs), and one reference formulation (CBP# Reference) containing an unrefined, commercial-grade combination of Al₂O₃ and SiC in place of the size-controlled additive. All formulations were rigorously characterized for their physical, mechanical, and tribological properties. The nano-Al₂O₃ formulation exhibited the highest density (2.197 g/cm³) and compressive strength (249.7 MPa), while the micro-SiC formulation achieved superior wear resistance, recording the lowest weight loss (0.0053 g) and the highest hardness (90 HV). The nano-SiC formulation offered the most balanced overall performance, combining high hardness (86.2 HV) with the highest average friction force (33.65 N) and the most stable friction-time response among all samples. The CNT-reinforced formulation produced the highest maximum friction force (42.07 N) but showed only moderate improvement in density, hardness, and compressive strength relative to the ceramic-reinforced samples. Compared with the CBP# reference, all five developed formulations exhibited higher hardness and coefficient of friction alongside lower weight loss, confirming their potential as durable, sustainable alternatives for automotive brake friction applications. Full article

Si₃N₄ ceramics with a YF₃-MgSiN₂ binary additive system were fabricated by hot pressing (HP) and spark plasma sintering (SPS) at 1500–1700 °C, followed by annealing at 1850 °C for 6 h. The effects of sintering route and temperature on phase transformation, microstructure evolution, thermal conductivity, and mechanical properties were systematically investigated. SPS significantly accelerated the α→β phase transformation compared with HP, and the β-Si₃N₄ content in SPS samples exceeded 94% at 1600 °C. After annealing, all samples were completely transformed into β-Si₃N₄, accompanied by obvious grain growth. Thermal conductivity was closely related to both grain size and relative density. Grain growth reduced grain-boundary phonon scattering, whereas density loss and residual porosity deteriorated heat transport. The mechanical properties were jointly governed by β-Si₃N₄ content, grain morphology, and porosity. Elongated β-Si₃N₄ grains promoted crack deflection and crack bridging, thereby improving fracture toughness, while excessive porosity reduced flexural strength. These results demonstrate that optimizing the balance between phase transformation, grain growth, and densification is essential for tailoring the thermal and mechanical performance of Si₃N₄ ceramics containing non-oxide sintering additives. 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

This study explores the direct growth of boron-doped diamond films on biocompatible silicon nitride (Si₃N₄) ceramic substrates using hot-filament chemical vapor deposition (HFCVD), with a view toward their use in implantable electrochemical biosensors. The focus of this work is the establishment of process–structure–property relationships relevant to biosensor performance, including microstructure, surface chemistry, wettability, and electrical behaviour. The effects of key deposition parameters, namely methane concentration, deposition pressure, and sample holder configuration, were analysed in relation to film microstructure, crystallographic orientation, surface chemistry, wettability, and electrical performance. Under low CH₄/H₂ ratios, microcrystalline diamond films with a pronounced (111) preferential orientation were obtained, enabling improved boron incorporation and electrical resistivity values within the range required for biosensor operation (≈1–10 kΩ). Surface analyses revealed partially hydrogen-terminated diamond layers enriched with oxygen-containing functional groups (C–O and C–O–C), which enhance surface wettability and are suitable for enzyme immobilization. Among the studied conditions, films deposited at 150 mbar and low methane flow displayed the most balanced combination of electrical conductivity, surface wettability, and microstructural stability. Overall, the results highlight the potential of boron-doped CVD diamond grown directly on Si₃N₄ as a robust and biocompatible material platform for future implantable biosensors, particularly for glucose monitoring applications. Full article

The rapid adoption of Wide Band Gap (WBG) semiconductor technologies, particularly Silicon Carbide (SiC) and Gallium Nitride (GaN), together with emerging Ultra-Wide Band Gap (UWBG) materials such as AlGaN, Aluminum Nitride (AlN), Diamond, β-gallium oxide (β-Ga₂O₃), and Hexagonal Boron Nitride (h-BN), is reshaping wafer-level electrical testing beyond the capabilities of conventional silicon-based probing infrastructures. The increasingly demanding electrical, thermal, and mechanical operating conditions of these devices require probe cards to evolve from passive interconnects into integrated multiphysics systems capable of supporting high voltages, high current densities, and fast switching transients. This review analyzes the fundamental design constraints governing advanced probe card technologies, including probe-to-wafer contact physics, electrothermal behavior, insulation requirements, parasitic effects, and high-frequency performance. Particular attention is devoted to Vertical MEMS probe card architectures, which enable high contact density, low parasitic inductance, and improved current-carrying capability, making them particularly suitable for modern WBG applications. Emerging solutions, including ceramic insulation structures, controlled-atmosphere testing environments, integrated sensing, and advanced thermal management techniques, are also discussed. Furthermore, the paper examines the evolution of wafer-level testing strategies, from conventional parametric screening to reliability-oriented methodologies inspired by burn-in procedures, highlighting the growing importance of body-diode characterization for early defect detection in SiC devices. Beyond reviewing the current state of the art, this work proposes a structured taxonomy of probe card technologies and outlines a technology roadmap linking future WBG and UWBG device requirements with the evolution of wafer-level testing infrastructures. Full article

To identify the key factors influencing the cracking behavior of fully ceramic microencapsulated (FCM) fuel, this study employed the MOOSE V1.3 multiphysics coupling platform and the cohesive phase-field fracture theory to simulate crack initiation and propagation in FCM fuel, with particular attention to the effects of particle spacing and residual pore in the matrix. Results showed that during early irradiation stages, in the absence of matrix defects, particle spacing had minimal influence on the distribution of the maximum principal stress. However, when residual pore was present in the SiC matrix, significant stress concentration occurred at the porosity sites, where the maximum principal stress was localized. Smaller particle spacing promoted crack initiation in the SiC matrix between adjacent particles and led to a higher number of cracks under the same fast neutron fluence. In the presence of residual pore, crack nucleation occurred at porosity sites even at low neutron fluence; at a fluence of 2.3 × 10²⁵ n/m², through-thickness cracks formed in FCM fuel containing residual pore, resulting in the loss of fission product containment capability. Full article

Building-integrated photovoltaics (BIPV) require front-glass materials that satisfy both aesthetic and functional requirements. In this study, colored glass for BIPV applications was fabricated on indium tin oxide (ITO)-coated glass substrates using Radio-Frequency (RF) magnetron sputtering with various ceramic targets, including metal oxides (MoO₃, WO₃, and SiO₂), a nitride (TiN), and Si. The fabricated samples were classified into red, yellow, and blue color families and evaluated in terms of optical transmittance, sheet resistance, and colorimetric properties. The color characteristics were quantitatively analyzed using CIELAB coordinates (L^*, a^*, and b^*) and CIE 1931 chromaticity coordinates (x, y). The results showed that the chromaticity distributions followed continuous material-dependent trajectories rather than random dispersion. Oxide-based coatings generally shifted toward the yellow region with relatively high lightness, whereas TiN-based coatings shifted toward the blue region with reduced lightness. In addition, transmittance analysis in the photovoltaic-relevant spectral range indicated that Si-based coatings exhibited relatively high optical transparency. The observed color variations are consistent with thin-film interference and the optical properties of the coating materials. This study focuses on the comparative evaluation of optical, electrical, and colorimetric characteristics. This study provides a comparative framework for color realization analysis and offers practical guidance for material selection in colored BIPV glass design. Full article

This study investigates the effect of SiC nanoparticle addition on the microstructure, interfacial reactions, and mechanical properties of Zn5Al3Ti active solder used for ultrasonic soldering of AlN ceramic to copper substrates. Composite solders containing 3 and 6 wt.% SiC nanoparticles were prepared and applied under flux-free ultrasonic soldering conditions. The solder alloys were evaluated by tensile testing, while the soldered joints were evaluated by shear strength testing. The solder microstructure and interfacial regions were characterized using SEM/EDS analysis. The results showed that the addition of SiC nanoparticles modified the microstructure of the Zn5Al3Ti solder and influenced the mechanical performance of the ceramic/metal joints. Among the investigated systems, the AlN/Zn5Al3Ti + 6 wt.% SiC/Cu joint exhibited the highest shear strength, reaching approximately 101 MPa. SEM/EDS observations revealed the formation of compact multilayered interfacial regions, including possible Cu–Zn intermetallic phases at the Cu/solder interface and Al–Ti–Zn-based reaction products near the solder/AlN interface. The improved joint performance may be attributed to the combined effect of SiC-induced microstructural modification, the presence of Si-containing particles, and the formation of compact metallurgical bonds. The results indicate that Zn5Al3Ti solder modified with 6 wt.% SiC nanoparticles is a promising material for producing strong AlN/Cu joints under the applied ultrasonic soldering conditions. Full article

Silicon nitride ceramics exhibit excellent structural strength and electromagnetic wave transmission performance, yet demonstrate significant thermal shock instability under extreme conditions. Boron nitride (BN), on the other hand, possesses outstanding thermal shock resistance and electromagnetic wave transmission properties but exhibits relatively lower structural strength. Compositing these two materials holds promise for developing an integrated material that combines high-temperature load-bearing capacity with wave transmission capability. This study employed spark plasma sintering (SPS) technology to systematically investigate how varying BN content affects the sintering densification process and microstructural evolution of Si₃N₄/BN composite ceramics. Furthermore, we elucidated the mechanisms by which material composition and processing parameters influence key mechanical properties, dielectric characteristics, and other multifunctional attributes of the composites, providing a theoretical foundation for synergistic optimization design. The results indicate that BN incorporation suppresses both the phase transition from α-Si₃N₄ to β-Si₃N₄ during sintering and the growth of elongated β-Si₃N₄ crystals: the former hinders densification while the latter promotes it, resulting in a dual competitive mechanism that initially increases followed by decreases in sintered density. The effects of BN content on elastic modulus and fracture toughness align with trends in sintering density, whereas hardness, flexural strength, dielectric constant, and dielectric loss all show a monotonically decreasing trend with increasing BN content. 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

Sintering additives play a decisive role in the densification behavior, mechanical properties, and thermal conductivity of silicon nitride ceramics. In this study, Mg₂Si and YH₂ were used as sintering additives for gas pressure sintering of silicon nitride based on the synergistic mechanism of “silicide silicon extraction-hydride dehydrogenation”. The regulation rules of the additives on ceramic densification, mechanical properties, and thermal conductivity were systematically investigated. Two optimization strategies were proposed for the technical route of replacing traditional oxide additives with non-oxide systems. (i) Rare-earth hydride YH₂ was used to replace traditional rare-earth oxides. It reacts with SiO₂ to achieve strong deoxidation and precisely regulate the liquid phase composition. (ii) Metal silicide Mg₂Si was used to replace metal oxides. It promotes the preferred growth of β-Si₃N₄ grains, consumes oxygen in the system, and reduces lattice defects. Mg₂Si introduces Si into the liquid phase, increasing the Si/O ratio, which lowers lattice oxygen content and supports higher thermal conductivity. YH₂ consumes SiO₂ on the Si₃N₄ surface, which reduces liquid phase oxygen content and inhibits lattice oxygen incorporation, promoting a liquid phase with a high N/O ratio. Compared with traditional Y₂O₃, YH₂ increases the Y₂O₃/SiO₂ ratio in the liquid phase. It promotes grain growth, reduces SiO₂ activity, and further improves the thermal conductivity of ceramics. Silicon nitride ceramics prepared by gas pressure sintering at 1750 °C with 3 wt.% Mg₂Si and 4 wt.% YH₂ composite additives exhibit the highest thermal conductivity of 87 W/(m·K), with a Vickers hardness of 14.36 GPa and a flexural strength of 643.15 MPa. This study provides an innovative idea for the preparation of high-performance silicon nitride heat dissipation substrates. Full article

Simultaneously achieving high densification, excellent mechanical properties, and high thermal conductivity remains challenging for aluminum nitride–silicon carbide (AlN-SiC) composites. In this study, fine-grained AlN-SiC composite ceramics were fabricated via in situ reaction hot pressing with the addition of small amounts of silicon (Si) and carbon (C). At an optimal sintering temperature of 1800 °C, the primary phase composition consisted of AlN, SiC and residual graphite, with an average AlN grain size of 0.94 μm. The Si additive melted and wetted the AlN matrix via capillary action, thereby providing sufficient kinetic driving force for densification. Meanwhile, the C additive not only removed oxygen impurities and purified grain boundaries but also reacted in situ with liquid Si to form SiC. The uniformly dispersed SiC particles inhibited the abnormal growth of AlN grains via the grain boundary pinning effect. Consequently, the relative density, flexural strength, and Vickers hardness of the obtained AlN-SiC ceramics reached 99.08%, 365 MPa and 22.58 GPa, respectively. At room temperature, the composite exhibited a thermal conductivity of 66 W/(m·K) and a thermal diffusivity of 32.6 mm²/s. This superior thermal performance is attributed to the purified grain boundaries, uniform SiC distribution, high densification, and tightly bonded SiC/AlN interfaces, which result in weak phonon interfacial scattering. Full article

To further improve the high-temperature dry sliding performance of Si₃N₄ ceramics, a CrAlN transition layer was introduced to improve interfacial stability, while Ag was incorporated as a solid lubricant into the CrAlN matrix. The effects of Ag content on the microstructure and mechanical properties of the coatings were systematically examined, and the tribological performance was evaluated from 25 °C to 550 °C under dry sliding conditions. The Ag concentration increased with increasing Ag target power and affected the morphology, nanoparticle distribution, surface roughness, and mechanical properties of the coatings. Among the tested samples, the coating containing 9.6 at.% Ag exhibited a comparatively favorable combination of mechanical properties within the investigated composition range, with a hardness of 11.5 GPa, an H/E ratio of 0.0913, and an H³/E² value of 0.096 GPa. Tribological tests showed that the average coefficient of friction decreased from 0.32 at 25 °C to 0.12 at 550 °C. This reduction may be associated with temperature-assisted Ag redistribution toward the worn surface and the possible development of Ag-rich surface features at elevated temperatures. However, the wear rate increased with temperature, reaching 3.6 × 10⁻⁵ mm³/(N·m) at 550 °C, suggesting that friction reduction was accompanied by increased material removal and possible near-surface weakening. These results indicate that controlling Ag content is important for balancing friction reduction and wear resistance in ceramic-based self-lubricating coatings. Full article