Junjie Song

Ceramics can be traditionally classified as structural and functional ones. However, the miniaturization and multi‐functionalization of various devices require ceramics to have both structural and functional properties. In this work, we aimed to develop structure‐function integrated ZrO₂–SiO₂ nanocrystalline glass–ceramics (NCGCs) by in situ formation of homogenously distributed amorphous carbon. By reducing the calcination temperature of carbon‐containing powder, organic carbon groups were partially retained in the powder and they transformed to amorphous carbon in the sintered NCGCs. At micrometer scale, the carbon was homogenously distributed in the NCGCs, avoiding the commonly encountered agglomeration problem of carbon fillers. The effects of carbon on the microstructure, mechanical properties, wear resistance, and dielectric properties of the NCGCs were investigated. Results showed that the in situ formed amorphous carbon was homogenously distributed in the ZrO₂ nanocrystallites. Meanwhile, the amorphous carbon strongly bonded with the ZrO₂–SiO₂ NCGCs. Only a small amount of carbon was combusted even after annealing at 1000°C for 3 h. The formation of amorphous carbon led to an improvement of nanohardness and wear resistance of the NCGCs, while slightly reducing Young's modulus and flexural strength. The electromagnetic wave transmission performances were improved due to the formation of amorphous carbon. The current study paves a new way for developing structure‐function integrated glass–ceramics through in situ formation of carbon. The prepared structure‐function integrated ZrO₂–SiO₂ NCGCs have great potential to be used as radome and antenna windows of aerospace aircrafts that work in harsh environment.

Titanium alloys have been widely used in aerospace and other fields due to their excellent properties such as light weight and high strength. However, the extremely poor tribological properties of titanium alloys limit their applications in certain special working conditions. In order to improve the tribological properties of titanium alloys, the zirconia coatings were prepared on the surface of a TC4 titanium alloy using the discharge plasma sintering method in this article. The influence of sintering parameters on properties such as density, adhesion, hardness, and phase composition, as well as tribological properties (friction coefficient, wear rate) were investigated, and the influence mechanism of the coating structure on its mechanical and frictional properties was analyzed. The results showed that, with the increase in sintering temperature, the density, bonding strength, and hardness of the zirconia coating were significantly improved. The zirconia coating prepared at a sintering temperature of 1500 °C and a sintering time of 20 min had the lowest friction coefficient and wear rate, which are 0.33 and 6.2 × 10⁻⁸ cm³·N⁻¹·m⁻¹, respectively. Numerical analysis showed that the increase in temperature and the extension of time contributed to the extension of the diffusion distance between zirconia and titanium, thereby improving the interfacial adhesion. The influence mechanism of different sintering temperatures and sintering times on the wear performance of zirconia coatings was explained through Hertz contact theory.

High-performance Al₂O₃/graphite-Al₂O₃ laminated composites exhibit an excellent self-lubricating ability for moving components, such as sliding shaft sleeves and dynamic seals. The tribological behaviors of Al₂O₃/graphite-Al₂O₃ laminated composites should be studied extensively under water working conditions. Here, we attempted to explore the practicability of the Al₂O₃/graphite-Al₂O₃ laminated composite as a sealing material from a tribological point of view under water lubrication conditions. The tribological properties and mechanism of friction and wear of laminated composite ceramics were investigated under dry sliding friction, water environment, and suspended particle working conditions. It was found that the Al₂O₃/graphite-Al₂O₃ laminated composite has a better friction performance under water lubrication compared to dry sliding because of the separation effects formed by a water molecule film and a transfer film. Meanwhile, the wear rate under dry contact was found to be approximately six times that under water lubrication conditions. Under the water lubrication conditions, the formation of graphite films and water-adsorbed layers improved the anti-wear properties of the laminated materials, and the friction coefficient and the wear rate were as low as 0.16 and 1.76 × 10⁻⁶ mm³/Nm, respectively. Under the suspended particle working condition, the solid particles destroyed the graphite lubricating film and abrasive wear dominated the wear mode. The Al₂O₃/graphite-Al₂O₃ laminated composite demonstrates a potential for application in dynamic sealing and sliding components.

The oxidation products (MoO ₃ and V ₂ O ₅ ) have low melting points and tend to sublimate at high temperatures despite that MoSi ₂ and VSi ₂ may possess good self‐lubricating properties. To cope with this challenge, a high‐entropy transition metal disilicide was designed in this work in which transition metal elements that could form high melting point oxides were deliberately added. The high‐entropy (Ti _0.2 V _0.2 Nb _0.2 Mo _0.2 W _0.2 )Si ₂ (HE‐MSi ₂ ) with hexagonal structure was successfully prepared by SPS using Ti, V, Nb, Mo, W, and Si powders as the initial materials in this work. The HE‐MSi ₂ presents a high hardness (11.8 ± 0.4 GPa) and elastic modulus (387.2 ± 46.8 GPa). In particular, its hardness is higher than that of the corresponding disilicides. Noteworthy, HE‐MSi ₂ demonstrated superior wear resistance when compared to Mo‐Si‐based ceramics (such as MoSi ₂ , Mo ₅ Si ₃ , and Mo ₅ SiB ₂ ), high‐entropy carbides (such as (MoTaWVTi)C, (HfMoNbTaTi)C, and (TiVNbMoW) _4.375 , and traditional single‐phase ceramics (including Sialon, Si ₃ N ₄ , Al ₂ O ₃ , SiC, and ZrO ₂ ). Meanwhile, at a high temperature of 600°C, the friction coefficient and wear rate were reduced to 0.64 ± 0.05 and (1.88 ± 0.15)×10 ⁶ mm ³ /N·m, respectively. The preferential oxidation of different elements of the HE‐MSi ₂ was validated through systematical characterization of composition evolution, which was dominantly impacted by high temperature and friction induction.

Synthetic zircon (ZrSiO₄) ceramics are typically fabricated at elevated temperatures (over 1500 ºC), which would lead to high manufacturing cost. Meanwhile, reports about preparing ZrSiO₄-based ceramic composites via controlling the solid-state reaction between ZrO₂ and SiO₂ are limited. In this work, we proposed a low-temperature strategy to flexibly design and fabricate ZrSiO₄-based ceramic composites via doping and tuning the solid-state reaction. Two ceramic composites and one ceramic were in situ prepared by reactive fast hot pressing (FHP) at approximately 1250 ºC based on the proposed strategy, i.e., a ZrSiO₄-SiO₂ dual-phase composite with a bicontinuous interpenetrating and hierarchical microstructure, a ZrSiO₄-ZrO₂ dual-phase composite with a microstructure of ZrO₂ submicron- and nano-particles embedded in a micron ZrSiO₄ matrix, and a ZrSiO₄ ceramic with a small amount of residual ZrO₂ nanoparticles. Results showed that phase compositions, microstructure configurations, mechanical properties, and wear resistance of the materials can be flexibly regulated by the proposed strategy. Hence, ZrSiO₄-based ceramic composites with different properties can be easily fabricated based on different application scenarios. These findings would offer useful guidance for researchers to flexibly fabricate ZrSiO₄-based ceramic composites at low temperatures and tailor their microstructures and properties through doping and tuning the solid-state reaction.

The catastrophic fracture characteristics of ceramic materials have become one of the most serious factors limiting their application in critical areas, as a result, it is urgent to overcome the brittleness and improve the damage tolerance of ceramic materials. Herein, a series of Al ₂ O ₃ composite ceramics developed with short Al ₂ O ₃ fibers and a compound interface phase composed of Al ₂ O ₃ and h ‐BN powders, followed by investigating their fracture behaviors and damage tolerance. Results show that these composites present progressive fracture manners with the rising resistance curve (R‐curve) behaviors, and the maximum crack growth toughness of the sample with 15% compound interface phase reaches above 10 MPa·m ^1/2 (135% increase with respect to the reference alumina). Meanwhile, the composite ceramic exhibits an excellent ability to resist catastrophic failure with a large critical crack size (105.47 ± 19.11 μm) and high damage tolerance parameter (0.71 ± 0.06 m ^1/2 ), which are close to 14.57 times and 5.92 times higher than those of the reference alumina. The superior performances are mainly attributed to the precise combination of compound interface phase for inducing crack and interlocking Al ₂ O ₃ fibers for load capacity.

As an excellent light metal material, titanium alloy has an important application in high technology equipment. In this study, the composite lubrication structure was prepared on the titanium alloy surface by combining the surface texture, thermal oxidation layer, and polytetrafluoroethylene (PTFE)-based lubricating coating. The effect of texture parameters and thermal oxidation layer on the fretting wear behavior of the composite lubrication structure was evaluated under a load of 50 N. The results showed that the PTFE-based lubricating coating on the textured surface showed excellent friction-reduction and anti-wear effect compared with the coating on the single smooth surface and thermal oxidation surface. The introduction of a thermal oxidation layer on the textured surface further improved the fretting wear life of lubrication coating. The friction coefficient and wear rate can be as low as 0.242 and 2.3 × 10⁻⁵ mm³·N⁻¹m⁻¹, respectively, under dry fretting contact conditions. Compared with the untextured surface, the longevity of the composite lubrication structure is extended by more than 90%.

Natural composites have very simple compositions and complex hierarchical architectures consisting of several different levels. These features simultaneously endow them with strength, toughness, functional adaptation, and damage‐healing characteristics. Inspired by the microstructural features of natural materials, this work successfully fabricated Al₂O₃/reduced graphene oxide (rGO) fibrous monolithic ceramics with bamboo‐like structures by introducing a thin graphene oxide around Al₂O₃ fiber cells to form the rGO boundary phase. The detailed evolutions of the crack extension and fracture responses were investigated by a J‐integral method, and these bamboo‐like composites demonstrated high structural reliability with excellent damage tolerance and progressive plastic failure behavior. With the fiber cell diameter of 0.6 mm, such composites exhibited fracture toughness (29.46 ± 3.04 MPa m^1/2) and work of fracture (799 ± 127 J m⁻²) that were 475% and 1075% higher than those of the monolithic Al₂O₃ ceramic, respectively. Their excellent fracture‐resistant behavior was attributed to the hierarchical architectures that provide crack deflection, delamination, and load redistribution. The results also established the structure‐activity relationships to guide the design and fabrication of these bamboo‐like composites.

Fabrication of fibrous monolithic ceramic with bamboo‐like structures is a promising method to improve the mechanical properties of ceramics through extrinsic reinforcement. Nevertheless, heterogeneous boundaries are easily oxidized at high temperatures, which seriously limits the long‐term use of these materials when employed in high‐temperature and high/low‐temperature alternating environments. In this study, a “plain” ceramic—a single‐component and complex‐structure Al ₂ O ₃ ceramic—was successfully designed and prepared using nano‐sized Al ₂ O ₃ as polycrystalline fibers and micro‐sized Al ₂ O ₃ as boundaries to obtain a structure with a fibrous monolithic architecture. Self‐toughening of Al ₂ O ₃ ceramics can be achieved by introducing hierarchical architectures derived from the difference between grain sizes of fibers and boundaries, which gives the ceramics high fracture toughness and reliability. Moreover, the material demonstrated a low friction coefficient and high wear‐resistance properties when coupled with C/C composites at room temperature, 800°C, and in the alternating temperature enviroment between room temperature and 800°C.