Transmission Electron Microscope Study on the Structure around Fatigue Cracks of α-iron

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  • Transmission Electron Microscope Study on the Structure around Fatigue Cracks of α-iron

Abstract

Fatigue tests of thin-foil α-iron were conducted at room temperature and 400°C, and defect structure around a fatigue crack formed in the foil was observed using a 500 kV electron microscope. The main results obtained are: (1) Well-developed substructure was formed around a fatigue crack of α-iron both at room temperature and at 400°C. (2) Extremely small subgrains (\lesssim1μ) and strain-concentrating-region were also found in a thin layer adjacent to fatigue cracks. (3) Several voids or microcracks were always formed in front of the tip of a fatigue crack. (4) The raise of testing temperature resulted in the increased width of strain-concentrating-region, the increased number of voids and the formation of helical dislocation and rows of loops along the ⟨111⟩ direction.<BR>Based on these observations, the growth of fatigue cracks via the formation and linking of voids was suggested. Void formation due to migration and coagulation of vacancies, which had already been proposed for aluminium, was also shown to be possible in α-iron.

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