ELEVATED TEMPERATURE CRACK GROWTH STUDIES OF ADVANCED TITANIUM ALUMINIDE

ORDERED INTERMETALLIC TITANIUM ALUMINIDE TI(3)AL ALLOYED WITH NIO0 BIUM POSSESSES ATTRACTIVE HIGH TEMPERATURE PROPERTIES AND MODERATE LOW TEMPERTURE DUCTIVILITY, BUT APPLICATION IS LIMITED TO STATIC COMPONENTS IN AIRCRAFT GAS TURBINE ENGINES. TO EXTEND THEIR USE TO ROTATING PARTS OF TURBINE ENGINES, BETTER UNDERSTANDING OF LIFE LIMITING PROCESSES SUCH AS CREEP/FATIGUE CRACK GROWTH AND FRATURE IS REQUIRED. PHASE I RESEARCH INVOLVES INVESTIGATION OF FATIGUE CRACK GROWTH IN TI(3)AL PLUS NIOBIUM, INCLUDING STUDY OF ENVIRONMENTAL EFFECTS ON CRACK BEHAVIOR. MECHANICAL TESTING WILL BE CONDUCTED USING A MINICOMPACT TENSION TYPE SPECIMEN UNDER LABORATORY AIR AND VACUUM ENVIRONMENTS, WITH TEMPERATURES RANGING FROM ROOM TEMPERATURE TO 649 DEG C (1200 DEG F). TWO HEAT TREATMENT PROCEDURES ARE SELECTED TO PROVIDE DIFFERENT BASELINE MICROSTRUCTURE. CONSTANT LOAD AMPLITUDE FATIGUE CRACK GROWTH TESTS WILL BE CONDUCTED IN A SERVO-HYDRAULIC MTS TESTING MACHINE UNDER COMPUTER CONTROL. DETAILED FRACTO GRAPHIC ANALYSIS OF ALL FRACTURE SPECIMENS USING A SCANNIG ELECTRON MICROSCOPE IS ALSO PLANNED. RELATIONSHIPS BETWEEN THE MICROSTRUCTURE AND FRACTURE MORPHOLOGY WILL BE EVALUATED. A COMPARISON BETWEEN THE AIR AND VACUUM CRACK GROWTH DATA WILL BE MADE TO UNDERSTAND ENVIRONMENTAL INFLUENCE. RESULTS OF PHASE I PRELIMINARY DATA WILL BE USED TO SELECT AN OPTIMUM ALLOY DESIGN AND DERIVE A WORK PLAN FOR PHASE II RESEARCH.