Abstract
The effect of atmospheric-corrosion on the fatigue crack nucleation and fracture surface morphology in the early stage of fatigue has been investigated by tests in air and vacuum on pure iron. The experiments were conducted under push-pull loading, and both external and fractured surfaces were observed by means of optical and scanning electron microscopy.It was found that the fatigue lives of iron in vacuum were 2.1 times those in air and the fatigue limit was also 1kg/mm2 higher in vacuum than in air. The density of slip lines in the specimens tested in vacuum was much higher than that in air and the cyclic numbers up to fatigue crack nucleation in vacuum were found to be 2.6 times those in air. The morphology of initial transcrystalline fracture surfaces in air was classified in two types and the number of intercrystalline fracture surfaces was decreased as stress amplitude increased. The morphology of initial transcrystalline surfaces in vacuum was similar to that in air. No intercrystalline fracture surfaces were observed in the specimens tested in vacuum. Clear striations were found on the fracture surfaces of the specimens tested in vacuum, though most of the surfaces have a flattened and smeared appearance.
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