Abstract
BN/La-Al-Si-O composite ceramics were fabricated by hot-pressed sintering using hexagonal boron nitride (h-BN), lanthanum oxide (La2O3), aluminia (Al2O3), and amorphous silica (SiO2) as the raw materials. The effects of sintering temperature on microstructural evolution, bulk density, apparent porosity, and mechanical properties of the h-BN composite ceramics were investigated. The results indicated that La-Al-Si-O liquid phase was formed during sintering process, which provided an environment for the growth of h-BN grains. With increasing sintering temperature, the cristobalite phase precipitation and h-BN grain growth occurred at the same time, which had a significant influence on the densification and mechanical properties of h-BN composite ceramics. The best mechanical properties of BN/La-Al-Si-O composite ceramics were obtained under the sintering temperature of 1700 °C. The elastic modulus, flexural strength, and fracture toughness were 80.5 GPa, 266.4 MPa, and 3.25 MPa·m1/2, respectively.
Highlights
IntroductionHexagonal boron nitride (h-BN) and its matrix composite ceramics are typical structural-functional ceramics that
Hexagonal boron nitride (h-BN) and its matrix composite ceramics are typical structural-functional ceramics thatJ Adv Ceram 2021, 10(3): 493–501 added to improve the properties of hexagonal boron nitride (h-BN) composite ceramics [12,13,14,15,16].Some researches have been investigated on the microstructural evolution during sintering and the properties of h-BN ceramics [17,18,19,20,21]
It could be obviously observed that the grain size of h-BN became bigger with increasing sintering temperature, because the liquid phase had better heat and mass transfer effect at higher temperatures to promote the growth of h-BN grains
Summary
Hexagonal boron nitride (h-BN) and its matrix composite ceramics are typical structural-functional ceramics that. Higher sintering pressure was more favorable to the preferred orientation growth of the in-plane direction of h-BN grains along the pressure direction, and higher sintering temperature promoted the mass transfer and grain growth They referred that the structural fluctuation of amorphous BN resulted in the turbostratic boron nitride (t-BN) phase formation during the sintering process, and stacking faults usually existed in the as-grown h-BN grains [22]. The sintering pressure had a great influence on the mechanical properties of composite ceramics, and on the crystallization of MAS and structural order of h-BN. La–Al–Si–O glass phase has been reported on promoting sintering densification and improving the room/elevated-temperature mechanical properties of h-BN matrix composite ceramics [33,34,35,36,37]. The corresponding mechanical properties were tested to reveal the influence of microstructural evolution on the performance of composite ceramics
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