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Whiskers have been extensively used in ceramics as excellent reinforcing phases during the past decades. Despite in-depth investigation of whisker-reinforced ceramics (WRC), however, the time-consuming, environmentally unfriendly, content design blindness of experimental method as well as pathogenicity of whiskers force people to explore quick and green research approaches. Therefore, this work aims at developing a modeling approach of WRC and predicting the mechanical properties of WRC, thereby compensating for the disadvantages of traditional experimental method. Initially, a modeling approach of WRC based on Voronoi tessellation was presented. Then, taking β-Si 3 N 4w and Si 3 N 4 as research objects, the prediction models of mechanical properties of 0–6 wt% β-Si 3 N 4w -reinforced Si 3 N 4 ceramics (SWRSC) were established. Finally, the effect of β-Si 3 N 4w content on mechanical properties of Si 3 N 4 -based ceramics was discussed, and the enhancement mechanism of β-Si 3 N 4w was revealed. Results indicated that the flexural strength of SWRSC was significantly advanced with increasing β-Si 3 N 4w content. Crack deflection and intergranular fracture induced by β-Si 3 N 4w as well as load-bearing effect of β-Si 3 N 4w were the mainly responsible for the reinforcement of Si 3 N 4 -based ceramics. The enhancement mechanisms, previously observed experimentally, were effectively simulated. The fracture toughness reached a maximum of 6.17 MPa m1/2 when β-Si 3 N 4w amount was 1 wt%, which was approximately 36.50% higher than monolithic Si 3 N 4 ceramic. The predicted value of β-Si 3 N 4w optimal content was consistent with relevant experimental conclusions. When β-Si 3 N 4w content was 3 wt%, the hardness of Si 3 N 4 -based ceramics reached the maximum value of 23.21 GPa. The effectiveness of prediction results and the presented modeling method were confirmed by comparing with related test values. [ABSTRACT FROM AUTHOR]

The trial-and-error method used in ceramics research has certain limitations such as the high blindness of material component design. Moreover, calculations of the toughness of ceramics using the extended finite element method, which is the most broadly applied technique, are complicated. To overcome these issues, in this study, multilayer graphene (MLG)/Si 3 N 4 whisker (Si 3 N 4w)-reinforced Si 3 N 4 ceramics (MWSCs) were used as the model material, and the modeling of MWSCs was conducted using Voronoi tessellation. Additionally, a more concise novel approach was applied for the prediction of the fracture toughness of MWSCs. Furthermore, the optimal MLG and Si 3 N 4w contents were predicted, and then they were verified by fabricating MWSCs using spark plasma sintering (SPS). Simulation results indicated that the optimum MLG and Si 3 N 4w contents to enable the toughness and hardness to reach the maximum values (9.87 MPa·m1/2 and 23.19 GPa) were 1 wt% and 3 wt%, which were consistent with the experimental results. Consequently, the effectiveness of the proposed method was verified. Moreover, the experimental values of the maximum fracture toughness and hardness were 11.04 MPa·m1/2 and 20.29 GPa, which were 47.20% and 12.10% higher than those of Si 3 N 4 ceramics reinforced with 1 wt% MLG, respectively. The synergistic toughening effects of MLG and Si 3 N 4w were significantly reflected. The load-bearing effect, bridging, and crack deflection induced by MLG and Si 3 N 4w were the key reasons for the improvement in the mechanical properties of MWSCs. [ABSTRACT FROM AUTHOR]

Exploring ceramic-based self-lubricating materials with low coefficient of friction (COF) has become one of the hot directions to advance the service performance and life of high-end equipment. In this work, the tribological properties of multilayer graphene (MLG)/β-Si 3 N 4 whisker (β-Si 3 N 4w)/Si 3 N 4 ceramics were investigated. The effects of load and linear speed on the dry sliding COF were discussed. The friction-reducing and self-lubricating mechanisms of MLG and β-Si 3 N 4w were deeply analyzed according to the wear morphology and mechanical properties of Si 3 N 4 -based ceramics. The friction frequency was proposed to analyze the wear mechanism. Results indicated that MLG and β-Si 3 N 4w led to a breakthrough reduction in COF. At the load of 5–20 N, the COF reached an ultra-low level of 0.04–0.07, which was a further 89.86% lower than the reported studies. The comprehensive enhancement of mechanical properties and the existence of MLG lubricating film were the mainly responsible for the ultra-low COF. The COF of MLG/β-Si 3 N 4w /Si 3 N 4 ceramics raised to 0.24–0.31 at 50–200 mm/s, but it was still 33.88–47.64% lower than that of graphene/Si 3 N 4 ceramics. The increase in COF was attributed to the high wear induced by the raised friction frequency. The furrow wear and adhesive wear were the main wear forms of MLG/β-Si 3 N 4w /Si 3 N 4 ceramics. [ABSTRACT FROM AUTHOR]

Lead-free perovskites are a new type of luminescent material with non-toxic, stability and excellent photoelectric properties, which have great application in the field of photoelectric detection, solar cells, bio-imaging, etc. Here, we reported a new kind of uniform spherical rare-earth based double perovskite Cs 2 NaYCl 6 nanocrystals (NCs) as versatile hosts to accommodate ionic dopants for improving photoelectric properties especially the luminescent properties. In contrast to the low quantum yield of only 5.62%, the luminescent intensity of Cs 2 NaYCl 6 NCs can be impressively enhanced via doping Sb3+ and Mn2+ ions in the rare earth-based double perovskite lattices. For the Sb3+-doping, the photoluminescence quantum yield (PLQY) increases from 5.62% to 22.48%. On this basis, the luminescence colors can be tuned from blue to white and red via Mn2+ ions doping and the maximum PLQY can be further improved to 38.66%. Finally, the Sb3+, Sb3+/Mn2+ ions doped Cs 2 NaYCl 6 NCs based blue, red and white LEDs were explored, which indicates that these are potential materials in multicolor LEDs applications. [ABSTRACT FROM AUTHOR]

Herein, a microscale simulation method for the prediction of mechanical properties and composition design of multilayer graphene (MLG)-reinforced ceramic bearings was presented. The method aims at improving the toughness of the ceramic bearings and overcoming the disadvantages of the trial-and-error approach implemented in the research of ceramic bearings. Considering the most widely used Si 3 N 4 ceramic bearing as an example, the microscale models of 1–4 wt% MLG-reinforced Si 3 N 4 ceramic bearings were established using the Abaqus software and on the basis of the ASTM standards. The simulation results obtained through the proposed method and the previously reported experimental results for the mechanical properties demonstrated good agreement. The simulated optimal MLG content value of 1 wt% was consistent with that reported in previous studies, which confirmed the effectiveness of the proposed method. The flexural strength and fracture toughness of the MLG-reinforced Si 3 N 4 ceramic bearings reached the maximum values of 761.77 MPa and 7.23 MPa m1/2 upon the addition of 1 wt% MLG, which were enhanced by 25.85% and 59.96%, respectively, compared with monolithic Si 3 N 4 ceramic bearing. Conversely, the introduction of MLG imparted a softening effect on the Si 3 N 4 ceramic bearings and, therefore, showed reduction in bearing hardness. Moreover, the MLG bridging phenomenon, previously observed experimentally, was revealed through simulation for the first time, which provided an explanation for the toughening mechanism. [ABSTRACT FROM AUTHOR]

The poor thermal properties of ceramics limited its wide application. Recently, upgrading via reinforcing ceramics with graphene has been recognized as a feasible approach to enhance the thermal performance of ceramics, and then advance the applications due to the exceptional thermal properties of graphene. Thus, this review summarized the latest advances in manufacturing process, microstructure as well as the thermal properties of graphene reinforced ceramics (GRC), highlighting the impacts of sintering techniques, sintering parameters and graphene/ceramic matrix parameters on the thermal performance of GRC. Furthermore, microstructure model simulation was proposed as a supplement to the traditional trial and error method, so as to facilitate the research associated with GRC. Besides, the challenges coupled with outlook for GRC with the superior thermal properties were also envisioned to providing readers with deep understanding of future development of GRC. [ABSTRACT FROM AUTHOR]