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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]

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]

This work aimed at investigating the superiorities of multilayer graphene (MLG) and β-Si 3 N 4 whisker (β-Si 3 N 4w) in synergistically enhancing the toughness of Si 3 N 4 ceramic composites. First, Si 3 N 4 ceramic composites with hybrid 1 wt% MLG and 0 – 5 wt% β-Si 3 N 4w were sintered by spark plasma sintering. Phase constitutions and microstructures of Si 3 N 4 -based ceramic composites were characterized by X-rays diffraction, Raman spectra, and scanning electron microscope. Then, the optimal β-Si 3 N 4w content and sintering process of MLG/β-Si 3 N 4w -toughened Si 3 N 4 ceramic composites were comprehensively optimized by orthogonal experiments. Results indicated that in the case of maintaining the hardness of 15.87 – 18.84 GPa, the fracture toughness of Si 3 N 4 ceramic composites incorporated with 1 wt% MLG and 3 wt% β-Si 3 N 4w was advanced to 11.04 MPa·m1/2, which was 11.29% and 87.12% higher than that of 1 wt% MLG- and 3 wt% β-Si 3 N 4w -reinforced Si 3 N 4 ceramic composites, respectively. Orthogonal experiments demonstrated that 1 wt% MLG/3 wt% β-Si 3 N 4w -toughened Si 3 N 4 ceramic composites sintered at 1600 ℃, 40 MPa, and holding time for 6 min had optimum comprehensive mechanical properties. MLG wrapping and the synergistic effects of pull out, crack deflection, crack branching, and bridging resulted by MLG and β-Si 3 N 4w were the main responsible for the enhancement of toughness. [Display omitted] • MLG/β-Si 3 N 4w synergistic toughened Si 3 N 4 ceramics were sintered by SPS. • Fracture toughness of Si 3 N 4 -based ceramics was enhanced to 11.04 MPa·m1/2. • Optimal contents of MLG and β-Si 3 N 4w were 1 wt% and 3 wt%. • Optimum sintering process were 1600 ℃, 40 MPa, and holding time for 6 min. [ABSTRACT FROM AUTHOR]

Combining the advantages of spark plasma sintering (SPS) and incomplete sintering (IS) in preparation of Si 3 N 4 ceramics, the spark plasma incomplete sintering (SPIS) was presented to fabricate porous Si 3 N 4 ceramics. Considering balancing the contradictory relationship between the porosity and toughness, 1 wt% multilayer graphene (MLG) was incorporated into porous Si 3 N 4 ceramics. Meanwhile, for the sake of compensating for the decrease in the hardness of porous Si 3 N 4 ceramics induced by MLG, 0–8 wt% β-Si 3 N 4 whisker (β-Si 3 N 4w) were synergistically added. The element distribution, phase constitutions and microstructures of MLG/β-Si 3 N 4w -reinforced porous Si 3 N 4 ceramics were characterized by energy dispersive spectroscopy (EDS), x-rays diffraction (XRD) and scanning electron microscope (SEM). The effects of β-Si 3 N 4w content on porosity, hardness and fracture toughness of porous Si 3 N 4 -based ceramics were analyzed. Results indicated that the porosity of porous Si 3 N 4 -based ceramics reached 21%, and then decreased significantly after the β-Si 3 N 4w content exceeded 4 wt%. The hardness of porous Si 3 N 4 -based ceramics obtained the maximum value 2.81 GPa when β - Si 3 N 4w was added 8 wt%, which was 31.92% higher than monolithic porous Si 3 N 4 ceramic. The mass transfer, diffusion and fusion induced by β-Si 3 N 4w were considered to be the main responsible for the increase of hardness. The fracture toughness of specimen with 1 wt% MLG and 4 wt% β-Si 3 N 4w was advanced to 3.14 MPa m1/2, which was 15.44% higher than monolithic porous Si 3 N 4 ceramic. The markedly enhanced of the fracture toughness was attributed to the synergistic effects of crack deflection, pull-out and bridging resulted by MLG/β-Si 3 N 4w. • Spark plasma incomplete sintering was proposed to fabricate porous Si 3 N 4 ceramics. • MLG/β-Si 3 N 4w were doped into porous Si 3 N 4 ceramics to advance its strength. • MLG/β-Si 3 N 4w -enhanced Si 3 N 4 ceramics with a porosity of 21% were prepared at 1500 °C. • Hardness of MLG/β-Si 3 N 4w -reinforced porous Si 3 N 4 ceramics reached 2.81 GPa. • Fracture toughness of porous Si 3 N 4 -based ceramics was improved to 3.14 MPa m1/2. [ABSTRACT FROM AUTHOR]