NITRIDE

CURRENT DENSE SI3N4 MATERIALS HAVE HIGH STRENGTH AND MODERATE TOUGHNESS AND ARE EXCELLENT CANDIDATES FOR APPLICATIONS SUCH AS CUTTING TOOLS AND HEAT ENGINE COMPONENTS. IMPROVEMENTS IN TOUGHNESS, CREEP RESISTANCE, THERMAL CONDUCTIVITY, HARDNESS AND WEAR OF SI3N4 ARE NEEDED FOR THESE AND OTHER APPLICATIONS. A POTENTIAL MEANS OF ACHIEVING THESE IMPROVEMENTS IS THROUGH THE ADDITION OF DISPERSED PARTICULATE PHASES. THE PROPOSED PHASE I PROGRAM WILL CONCENTRATE ON EVALUATING THE EFFECTS OF ADDITIONS OF 20 THROUGH 50% SIC PARTICLES AND WHISKERS TO SI3N4 STARTING MATERIALS, AND USE OF ALPHA VERSUS BETA SIC. BASELINE EVALUATION WILL INCLUDE DENSITY, FLEXURE STRENGTH, FRACTURE TOUGHNESS (KIC), HARDNESS AND MICROSTRUCTURE. SELECTED SPECIMENS WILL THEN HE FURTHER EVALUATED BY THERMAL CONDUCTIVITY MEASUREMENTS AND BY ACTUAL TESTING AS CUTTING TOOL INSERTS. DIRECTIONS FOR OPTIMIZATION WILL BE IDENTIFIED FOR STUDY IN PHASE II. ALTERNATE POWDERS (SUCH AS B4C, TIC, TIB2 AND ZRB2) WILL BE CONSIDERED IN PHASE II. LOW COST FABRICATION APPROACHES SUCH AS SINTER-HIP (HOT ISOSTATEC PRESS) ALSO WILL BE EVALUATED IN PHASE II.