Similar to Si_(3)N_(4)ceramics,β→a phase transformation in SiC ceramics plays a key role in tailoring the microstructures thus optimizing related properties.SiC microstructures are dominated with the core erim struc...Similar to Si_(3)N_(4)ceramics,β→a phase transformation in SiC ceramics plays a key role in tailoring the microstructures thus optimizing related properties.SiC microstructures are dominated with the core erim structures by AlN-solution,and by EBSD analysis,a-lamellae were revealed as stacking-faults(SF)and twin-boundaries(TB)in b-grains,co-existing with the coreerim structures asα/β→α’/β’transformation by sintering.The structural transformation can proceed much further by gas-pressuresintering than hot-pressing with only RE2O3 agents,while the latter retain a high-density of SF/TB in the metastable b-SiC grains.By high-angle secondary-electron imaging,nanoscale transition-layer(TL)was observed as an inter-phase to fully separate the core and rim,which is created by a transitory equilibrium in the solutionereprecipitation process.The enrichment of AlN or RE in TL demonstrates their segregation to core surface until reaching the super-saturation and before the growth of rims.With higher AlN or RE solution and after sintering,a shear stress can develop from TL contour to drive the expansion of SF/TB in Martensitic transition,especially under an external isotropic pressure.The combinations ofβ→a transformation,coreerim structures and viscous liquid-phase enable the comprehensive assessment of sintering-microstructure-property-performance relationship of SiC ceramics,as demonstrated for their creep behaviors and fracture toughness.展开更多
基金supported by the National Natural Science Foundation(Grant Nos.51532006 and 52032002)Shanghai Technical Service Center for Advanced Ceramics Structure Design and Precision Manufacturing(Grant No.20DZ2294000)supported provisionally by the Max-Planck Gesellschaft via the Max-Plack Partner Group in Shanghai Institute of Ceramics,Chinese Academy of Sciences through the years of 2003e2008.
文摘Similar to Si_(3)N_(4)ceramics,β→a phase transformation in SiC ceramics plays a key role in tailoring the microstructures thus optimizing related properties.SiC microstructures are dominated with the core erim structures by AlN-solution,and by EBSD analysis,a-lamellae were revealed as stacking-faults(SF)and twin-boundaries(TB)in b-grains,co-existing with the coreerim structures asα/β→α’/β’transformation by sintering.The structural transformation can proceed much further by gas-pressuresintering than hot-pressing with only RE2O3 agents,while the latter retain a high-density of SF/TB in the metastable b-SiC grains.By high-angle secondary-electron imaging,nanoscale transition-layer(TL)was observed as an inter-phase to fully separate the core and rim,which is created by a transitory equilibrium in the solutionereprecipitation process.The enrichment of AlN or RE in TL demonstrates their segregation to core surface until reaching the super-saturation and before the growth of rims.With higher AlN or RE solution and after sintering,a shear stress can develop from TL contour to drive the expansion of SF/TB in Martensitic transition,especially under an external isotropic pressure.The combinations ofβ→a transformation,coreerim structures and viscous liquid-phase enable the comprehensive assessment of sintering-microstructure-property-performance relationship of SiC ceramics,as demonstrated for their creep behaviors and fracture toughness.
