Abstract
The high-temperature fatigue properties of an Alloy 718 were investigated up to 107 cycles. Combined with the data for base metals and welded joints, the relationship between stress amplitude and number of cycles to failure (fatigue life) was characterized by two steps in the S–N curve. The fracture mechanisms were different between high and low stress levels. At high stress levels, fatigue fractures initiated from the specimen surface, whereas at low stress levels, the initiation was inside the surface. The internal fracture initiation sites were crystallographic flat facets of austenitic grains.
