Abstract
Effects of strain rate and strain wave shape on high temperature low cycle fatigue life of cast IN 738 nickel-base superalloy were investigated at 1123 K. Intergranular crack initiation and mixed crack propagation were observed mainly in slow-fast saw tooth wave, slow-slow triangular wave, and in truncated wave with hold time in tension and in both tension and compression tests. A reduction in the fatigue life of the specimens tested under these wave shapes, compared to those under fast-fast type of triangular wave shape, corresponded with a variation in the fracture mode. On the basis of a defined crack initiation criterion the test results were analyzed by the strain range partitioning method proposed by Manson, Halford, and Hirschberg. The observation that the wave shape effect on life was very sensitive when examined from the elastic strain range viewpoint suggested that a life prediction method that involves stresses may also be worthy of consideration.
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