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MoAlB is a ternary boride of MAB phases with strong resistance to oxidation and ablation at service temperature, thanks to preferential Al diffusion to form a protective oxide scale. However, excessive Al were often necessary in sintering of MoAlB ceramics, suggesting that a liquid-phase densification might occur thus leading to complex microstructures. By quantitative SEM analysis, ~17 mol.% Al 2 O 3 phase was found common in MoAlB ceramics. The liquid-phase of Al-Mo-B-O facilitates the direct conversion from MoB to MoAlB before in situ formation of Al 2 O 3. An intermediate Mo 3 Al 8 phase competes with layered conversion, which limits the insertion rate of Al into B-B layers of MoB to form abundant Al-deficient stacking-faults. Intermetallic Mo 3 Al 8 phase precipitates further in the intergranular regions parallel to the crystallization of Al 2 O 3 , leaving the reprecipitation of remaining Al. Both layered-conversion and intergranular oxides can improve ablation behavior for MoAlB ceramics, as well as fracture toughness and compressive strength. [Display omitted] [ABSTRACT FROM AUTHOR]

Ultrafast High-temperature Sintering (UHS) has been successfully applied to fabricate the silicon nitride (Si 3 N 4) bulks, as the first attempt of ultra-rapid consolidation of a non-oxide ceramics. At a heating rate of 875 °C/min, the bulk Si 3 N 4 ceramic with a relative density greater than 96 % and an α-β phase transformation degree above 80 % could be obtained within 300 s. The effects of ultrafast heating on the liquid phase sintering (LPS) were also comparatively studied. Results showed that, the ultrafast heating rate and high temperature under UHS might promote the LPS system evolving to a nonequilibrium state. By comparing with other pressureless sintering processes with much lower heating rates, UHS apart from reducing the processing time, and it is also an effective method to form a bimodal microstructure composed of interlocked rod-like β-Si 3 N 4 grains. [ABSTRACT FROM AUTHOR]