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A type of boron nitride–magnesium aluminum silicate (BN‐MAS) composite ceramics was fabricated by hot‐press sintering at different sintering temperatures. The relationship between the sintering temperature and microstructure was investigated by analyzing the interaction between hexagonal boron nitride (h‐BN) and the MAS phase. The main MAS phase in the composite ceramics is the α‐cordierite phase at a sintering temperature of 1300°C. At temperatures above 1400°C, the inhibitory effect of h‐BN on the crystallization of the MAS system is significant, and MAS mainly exists in the form of an amorphous phase. The composite sintered at 1700°C exhibited the highest bending strength of 218MPa. h‐BN and MAS were co‐enhanced. MAS can be used as an effective liquid‐phase sintering aid to assist in the sintering of h‐BN, whereas h‐BN can absorb the fracture energy of the composite ceramics through the pull‐out and bridging effect of the particles. [ABSTRACT FROM AUTHOR]

A type of hexagonal boron nitride-magnesium aluminosilicate composite ceramics was fabricated by hot-pressed sintering under different pressures. The relationships between sintering pressure, microstructure, and mechanical properties were investigated. The results indicate that sintering pressure has a great influence not only on the mechanical properties of composite ceramics, but also on crystallization of magnesium aluminosilicate (MAS) and structural order of hexagonal boron nitride. Under the given sintering pressure of 30 MPa, the fracture toughness of composites was greatly improved 66 % (from 2.49 to 4.12 MPa m, with similar densities). It also exhibits the highest bend strength of 245 ± 23 MPa. The fracture behavior of composites and the mechanism of sintering pressure which affect the crystallization of mullite in MAS were also discussed. [ABSTRACT FROM AUTHOR]

The fabrication of dense amorphous Si-B-C-N monoliths is a processing challenge given that it is hard to avoid crystallization at the sintering temperatures needed to attain full density up to 1900°C for conventional hot pressing and SPS methods. We report here successful densification of amorphous Si2BC3N monoliths achieved by heating at 1100°C and 5 GPa. The relationships between microstructure, types of chemical bonding, and mechanical properties were investigated. The strong amorphous 3-D networks of Si-C, C-B, C-N (sp³), N-B (sp³), and C-B-N bonds provide high densities at high applied pressure and thus amorphous Si2BC3N monoliths show high hardness of 29.4 GPa and elastic modulus of 291 GPa. The amorphous structure is lost with crystallization of β-SiC and BN(C) reducing contributions from Si-C, C-N (sp³), and C-B-N bond networks thereby decreasing mechanical properties. [ABSTRACT FROM AUTHOR]