FAST-PULSE HOT PRESSING OF SILICON CARBIDE COMPOSITES

SUPERHARD REFRACTORY MATERIALS HAVE IMPORTANT APPLICATIONS IN METAL SHAPING EQUIPMENT AND HEAT ENGINES DUE TO THEIR HIGH-TEMPERATURE STRENGTH AND HARDNESS. HOWEVER, THESE DESIRABLE ENGINEERING PROPERTIES ARE A MAJOR OBSTACLE TO THE FABRICATION OF USEFUL SHAPES. THESE MATERIALS ALSO SUFFER FROM LOW FRACTURE TOUGHNESS AS COMPARED TO MEALS. CONVENTIONAL PROCESSING METHODS AT OR NEAR EQUILIBRIUM CONDITIONS ARE LIMITED WITH RESPECT TO PEAK PRESSURE AND TEMPERATURE CAPABILITY. THEY ARE ALSO VERY LIMITED IN THEIR CAPABILITY TO PRODUCE HEAT-TREATABLE CERAMIC COMPOSITES. RESEARCHERS ARE APPLYING A NON-EQUILIBRIUM METHOD FOR CONSOLIDATION OF SILICON CARBIDE COMPOSITES CONTAINING AN ELECTRICALLY CONDUCTIVE PHASE. IN THIS PROCESS, A FINE POWDER MIXTURE IS SUBJECTED TO MECHANICAL PRESSURE AND AN INTENSE CURRENT PULSE WITH A DURATION THAT IS TYPICALLY LESS THAN A MILLISECOND. UNDER THESE CONDITIONS, THE CONDUCTIVE PHASE IS MELTED AND ALLOYED WITH THE SILICON CARBIDE PHASE WITH A MINIMUM OF HEAT LOSS TO THE CONTAINMENT STRUCTURE. THE RAPID COOLING OF THE COMPACT IS EXPECTED TO RESULT IN A HEAT-TREATABLE SOLID SOLUTION OR EXTREMELY FINE MICROSTRUCTURE.