IN-SITU DEVELOPMENT OF HIGH ASPECT RATIO BORIDE REINFORCEMENTS IN FINE GRAINED TIAL ALLOYS TO ENHANCE ELEVATED AND ROOM TEMPERATURE...

GAMMA-TIAL BASED INTERMETALLIC ALLOYS HAVE POTENTIAL AIR FORCE APPLICATIONS FOR TEMPERATURES UP TO 1800 DEG F. ALLOY DEVELOPMENT RESEARCH HAS SHOW THAT COMPOSITIONS (IN ATOM %) SUCH AS TI-48AL-2MN-2NB EXHIBIT SOME ROOM TEMPERATURE DUCTILITY AND GOOD HIGH TEMPERATURE OXIDATION RESISTANCE. HOWEVER, RESEARCH IS NECESSARY TO OPTIMIZE THE ROOM TEMPERATURE MECHANICAL PROPERTIES SUCH AS DUCTIVITY, TOUGHNESS AND IMPACT RESISTANCE, AS WELL AS THE HIGH TEMPERATURE MECHANICAL PROPERTIES SUCH AS TENSILE STRENGTH, FATIGUE AND CREEP GROWTH RATES. THE PROPOSED RESEARCH AIMS TO ACHIEVE OPTIMUM ROOM AND ELEVATED TEMPERATURE MECHANICAL PROPERTIES BY IN-SITU DEVELOPMENT OF A CRITICAL VOLUME FRACTION OF HIGH ASPECT RATIO BORIDE REINFORCEMENTS OF SIZE >10 MICROMETERS IN A FINE GRAINED (<10 MICROMETERS) GAMMA-TIAL MATRIX BY RAPID SOLIDIFICATION AND POWDER METALLURGICAL PROCESSING. BASED ON CONTINUUM MECHANICS CONSIDERATIONS, IMPROVE CREEP RESISTANCE IS EXPECTED FROM BORIDE REINFORCEMENTS. IMPROVED DUCTILITY IS EXPECTED FROM THE FINE GRAIN SIZE OF THE GAMMA-TIAL MATRIX BECAUSE OF THE REDUCED SLIP LENGTH AND THE LOWER STRESS CONCENTRATION AT THE GRAIN BOUNDARIES. PHASE I RESEARCH WILL INVESTIGATE THE EFFECT OF COLLING RATE 10(4)-10(6) K/S AND THE BORON CONTENT 0-10 AT % IN ORDER TO OBTAIN THE OPTIMUM MICROSTRUCTURE FOR THE DESIRED MECHANICAL PROPERTIES.