Search

In this paper, a honeycomb Si3N4 ceramic was fabricated by 3D printing with a well‐preserved structure. The effects of Si3N4 content on the rheological properties of Si3N4/sol–silica ink and the printing resolution of products were investigated. The microstructure, phase composition, liner shrinkage rate, and fracture behavior of printed samples before and after sintering were systematically characterized in detail. The results showed that the modified inks had the optimized rheological properties, and the stress–shear rate curves corresponding to each slurry could be well described by Bingham and Herschel–Bulkley fluid models. The corresponding slump rates of the printed samples with different Si3N4 to sol–silica mass ratios were all lower than 4%, and the linear shrinkage rate of all of the samples after sintering was below 20%. The fracture behavior under compressive loading of the honeycomb Si3N4 ceramics tended to be non‐catastrophic fractures both before and after sintering. The compressive strengths of all of the printed samples decreased with the increase of the Si3N4 content, and the highest compressive strength of the honeycomb ceramics could reach 131.2 MPa after sintering at 1600°C, which was about 366.9% higher than that of the samples in green state prior to the sintering. [ABSTRACT FROM AUTHOR]

The boron nitride reinforced fused silica (BN/SiO 2) ceramics are excellent high-temperature wave-transparent candidates, but encumbered by the unsatisfactory reliability and economy until now. Herein, promising BN whisker reinforced SiO 2 (BN W /SiO 2) ceramics are fabricated via hot-pressing, aiming to provide fundamental insight into their microstructural evolution, mechanical and dielectric properties. The densification behaviour and microstructural evolution are characterized by step-testing the sintering temperature and the BN W content, determining that SiO 2 matrix undergoes crystal nucleus breeding (≤1300 °C), followed by nucleation and growth (＞1300 °C), and BN W presents a uniform and stable structure (≤1350 °C) and skin-core structure (1450 °C), respectively. The underlying strengthening and toughening mechanisms are elucidated through constructing a multilevel porosity dependence of mechanical behaviour associated with the BN W content. Compared with 5 wt. % BN W /SiO 2 ceramic sintered at 1350 °C (S5-1350), the lightweight 20 wt. % BN W /SiO 2 ceramic sintered at 1300 °C (S20-1300) exhibits 619.1% higher machinability parameter while maintaining the mechanical properties. Moreover, the lightweight S20-1300 possesses a low dielectric constant (ε) of 3.77, loss tangent (tan δ) of 1.25 × 10-3 and coefficient of thermal expansion (CTE) of 1.34 × 10-6 K-1. The insights obtained from this study would help to advance the application of BN/SiO 2 ceramics in high-temperature radome. [ABSTRACT FROM AUTHOR]

The high-temperature service performance of nearly fully dense 20 wt% BN W /SiO 2 ceramic was systematically investigated. The oxidation damage and strength degradation of the whiskers combined with the surface microstructures of the samples predominantly influence the flexural strength from RT to 1000 °C. In previous work, the temperature dependence of the material properties is invariably ignored when evaluating thermal stress crack initiation and propagation behaviour. In this work, modified thermal shock models that include temperature-dependent material properties were established based on thermal-shock fracture (TSF) theory and thermal-shock damage (TSD) theory. Then, the thermal shock resistance (TSR) of the BN W /SiO 2 ceramic was evaluated by preforming a water quenching test. The modified models could better explain the TSR behaviour of the ceramic, indicating that considering the temperature-dependent material properties will reveal the thermal shock damage mechanism more precisely. [ABSTRACT FROM AUTHOR]

In this study, SiC whiskers (SCWS) reinforced geopolymer composites (SCWS/KGP) and their ceramic products (SCWS/leucite) were prepared, and effects of SiC whiskers contents on the microstructure and flexural strength of the SCWS/KGP and SCWS/leucite composites were investigated. The results show that the whisker addition has little influence on both phase composition and thermal shrinkage of the KGP composites, but a suitable content of whisker will result in the improved flexural strength, and when the SCWS content is 2 wt%, flexural strength of the SCWS/KGP composite is enhanced by 95% compared with the neat geopolymer. The flexural strength of the composites can be further enhanced significantly after the composites being treated at 1100 °C and 1200 °C and flexural strength of the composite with SCWS content of 2 wt% was 107% and 125% higher than the untreated counterpart, respectively. The increase in flexural strength of the composites should be attributed to the strong leucite formation, whisker debonding and pulling out from matrix during the fracturing process based on the good interfacial bonding state between whisker and leucite matrix. [ABSTRACT FROM AUTHOR]