PROCESSING AND CHARACTERIZATION OF SILICON CARBIDE-ALUMINUM OXYCARBIDE CERAMICS

SILICON CARBIDE (SIC), ALUMINUM OXYCARBIDE (A12OC), AND ALUMINUM NITRIDE (AIN) ALL HAVE THE SAME 2H WURZITE CRYSTAL STRUCTURE AND FORM A COMPLETE SOLID SOLUTION. RESEARCH IN THE SIC-ALN SOLID SOLUTION SYSTEM HAS SHOWN THAT THE CREEP CHARACTERISTICS OF THIS MATERIAL ARE VERY DESIRABLE FOR HIGH TEMPERATURE APPLICATIONS. IT IS BELIEVED THAT THE LOW CREEP RATE IS THE RESULT OF GRAIN BOUNDARIES DEVOID OF LOW MELTING PHASES. TO DATE IT HAS NOT BEEN POSSIBLE TO DENSIFY THE ALN-SIC SOLID SOLUTIONS WITHOUT HOT PRESSING. RECENT RESEARCH AT CERAMATEC HAS SHOWN THAT IT IS POSSIBLE TO OBTAIN DENSE SIC-AL2OC POLYCRYSTALLINE MATERIALS WHICH APPEAR TO FORM A COMPLETE SOLID SOLUTION. IT IS BELIEVED THAT THE ALUMINUM OXYCARBIDE KEEPS THE OXYGEN TIED UP IN THE LATTICE AND THE GRAIN BOUNDARIES WILL BE DEVOID OF LOW MELTING PHASES. THE PURPOSE OF THIS RESEARCH EFFORT IS TO CHARACTERIZE THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF THE SINTERABLE SIC-AL2OC MATERIALS IN ORDER TO DETERMINE IF THEY ARE CANDIDATES FOR USE IN THE HEAT ENGINES, CUTTING TOOLS, WEAR PARTS AND OTHER HIGH TEMPERATURE COMPONENTS. THE PROPOSED RESEARCH WILL FOCUS ON TWO METHODS OF SYNTHESIZING THE DESIRED SOLID SOLUTIONS AND OPTIMIZATION OF PROCESSING AND COMPOSITION WILL BE AN IMPORTANT ASPECT OF THE STUDY. X-RAY DIFFRACTION, TRANSMISSION ELECTRON MICROSCOPY AND ENERGY DISPERSIVE SPECTROSCOPY WILL BE USED TO CONFIRM THE EXISTENCE OF A SOLID SOLUTION IN THE PRESSURELESS SINTERED MATERIALS AND LOOK AT THE GRAIN BOUNDARY CHEMISTRY. ROOM TEMPERATURE FRACTURE TOUGHNESS, HARDNESS, FLEXURAL STRENGTH AND HIGH TEMPERATURE CREEP EXPERIMENTS WILL BE CONDUCTED TO ESTABLISH BASELINE PROPERTIES AND DETERMINE THE UTILITY OF USING THIS NEW MATERIAL IN HIGH TEMPERATURE APPLICATIONS. IT IS ANTICIPATED THAT SIC-AL2OC CAN BE USED TO REPLACE METAL BONDED CARBIDES (I.E. WC-CO) IN SOME CUTTING TOOL APPLICATIONS AND THEREBY REDUCE THE U.S. DEPENDENCE ON COBALT, A STRATEGIC METAL.