A STUDY OF FATIGUE FAILURE IN SUPERALLOYS USING POSITRON-ANNIHILATION

This study shows there are significant changes occurring in the open v olume defect concentration during fatigue cycling as measured by the S parameter. These changes are dependent upon the stress ratio, R = sig ma(min)/sigma(max), the maximum stress, sigma(max), and the number of fatigue cycles. The decline in the S parameter is due to the eliminati on of the residual vacancies' This decline is followed by an increase due to the generation of dislocations and the formation of small micro cracks. This is followed by a decline in the S parameter due to growth of the microcracks ultimately leading to failure.