ENVIRONMENT INFLUENCE ON THE DUCTILITY AND CRACK GROWTH BEHAVIOR OF GAMMA PRIME NICKEL ALUMINIDE (NI3AL)

ORDERED INTERMETALLIC NICKEL ALUMINIDE NI3AL MICROALLOYED WITH BORON POSSESSES ATTRACTIVE MECHANICAL PROPERTIES FOR STRUCTURAL USE AT ELEVATED TEMPERATURES. FOR ITS POTENTIAL APPLICATION IN THE AIRCRAFT GAS TURBINE ENGINE COMPONENTS, BETTER UNDERSTANDING OF THE STRUCTUREPROPERTY RELATIONSHIPS, ENVIRONMENTAL INFLUENCE AT ELEVATED TEMPERATURES AND LIFE LIMITING PROCESSES FOR THE MATERIAL IS REQUIRED. PHASE I RESEARCH INVOLVES INVESTIGATION OF ENVIRONMENTAL INFLUENCE ON THE DUCTILITY AND FATIGUE CRACK GROWTH BEHAVIOR OF NI3AL BY CONDUCTING TESTS IN LABORATORY AIR AND ULTRA HIGH VACUUM ENVIRONMENTS, WITH TEMPERATURES RANGING FROM ROOM TEMPERATURE TO 600 DEG C. TENSILE AS WELL AS CONSTANT LOAD AMPLITUDE FATIGUE CRACK GROWTH TESTS WILL BE CONDUCTED USING A SERVOHYDRAULIC TESTING MACHINE UNDER COMPUTER CONTROL. DETAILED FRACTOGRAPHIC ANALYSIS OF ALL FRACTURE SURFACES USING A SCANNING ELECTRON MICROSCOPE IS ALSO PLANNED. RELATIONSHIPS BETWEEN THE MICROSTRUCTURE AND FRACTURE MORPHOLOGY WILL BE EVALUATED. A COMPARISON BETWEEN THE AIR AND VACUUM TEST DATA WILL BE MADE TO UNDERSTAND THE ENVIRONMENTAL IMPACT. RESULTS OF PHASE I PRELIMINARY DATA WILL BE USED TO SELECT AN OPTIMUM ALLOY DESIGN AND DERIVE A WORK PLAN FOR PHASE II RESEARCH.