Search

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]

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]

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]