IMPROVED ELEVATED-TEMPERATURE FATIGUE LIFE BY ION BEAM PROCESSES

ION IMPLANTATION IS AN EFFECTIVE PROCESS TO CREATE COMPRESSIVE STRESS IN THE SUBSURFACE REGIONS OF METALLIC COMPONENTS AND THEREBY ENHANCE THEIR RESISTANCE TO FATIGUE-INITIATED FAILURES. ION IMPLANTATION OF LIGHT INTERSTITIAL IONS (SUCH AS BORON, CARBON, OR NITROGEN) INTO TITANIUM-BASED ALLOYS (OR FEEOUS ALLOYS) IS A MICROSCOPIC SHOT PEENING PROCESS THAT TENDS TO REMOVE THE GRAIN BOUNDARIES AND CREATES TREMENDOUS COMPRESSIVE STRESS ON THE SURFACE OF TREATED COMPONENTS. THE CHANGES IN CRYSTAL STRUCTURE AND THE RESIDUAL STRESS ARE THE UNDERLYING REASONS FOR THE SLOWDOWN IN THE CRACK INITIATION PHASE AND CRACK PROPAGATION MODE. THE FATIGUE-RESISTANCE INITIATED BY ION IMPLANTATION IS STABLE AT HIGH TEMPERATURES. IN ADDITION THE PROCESS HAS BEEN SHOWN TO BE VERY EFFECTIVE TO MINIMIZE GALLING, FRETTING FATIGUE (ESPECIALLY IN TITANIUM BASED ALLOYS) AND NOTCH CREATION (IN HANDLING OF TITANIUM ALLOYS) THAT CAN GIVE RISE TO FATIGUE FAILURE. CONVENTIONAL ALPHA AND BETA TITANIUM ALLOYS AND ESPECIALLY THE HIGH TEMPERATURE ALUMINIDE (TIAL AND TI(3)AL) ALLOYS WILL BE ION IMPLANTED IN THIS PROGRAM. CHANGES IN COMPRESSIVE STRESS WILL BE QUANTITATIVELY EVALUATED. FATIGUE PROPERTIES WILL BE MEASURED AS WELL AS ANY CHANGES IN OTHER MECHANICAL AND CHEMICAL PROPERTIES.