PROCESSING,MICROSTRUCTURE,AND PROPERTIES OF REACTIVE HOT-PRESSED B_4C/SiC COMPOSITES

摘要

Monolithic boron carbide has been the ceramic of choice in the development of lightweight passive armor technologies.Future soldier and vehicular weight constraints have placed renewed emphasis on the development of materials with heterogeneous microstructures for improved damage-tolerance.Fully dense boron carbide/silicon carbide composites were produced via reactive hot-pressing silicon hexaboride and carbon black powder mixtures.The resulting boron carbide and silicon carbide(beta)phases appear to be continuous and interpenetrating.Zirconium diboride and residual amorphous carbon were also detected.The microstructure consists of three regions:(1)uniformly dispersed silicon carbide,(2)large boron carbide grains surrounded by agglomerated silicon carbide grains,and(3)agglomerated silicon carbide grains.The latter regions were responsible for degrading the flexural strengths of the composites.However,the mechanical properties were comparable to a commercially available armor-grade boron carbide.The irregular nature of the fracture surfaces indicates that the composites may exhibit R-curve behavior for suitably short-cracks.Long-crack fracture toughness values do not indicate any significant increases over monolithic boron carbide.