疲労き裂先端近傍の転位組織の直接観察 (鉄)
1976 年 25 巻 269 号 p. 145-150
詳細
1976 年 25 巻 269 号 p. 145-150
In this paper, the method of jet-electropolishing is described, by which few-microns thick foil specimens containing a considerably sharp crack can be prepared from bulk fatigued-specimens of iron, and the substructures in the vicinity of the cracks observed through a 2000kV electron microscope are shown. They are; (1) a fine cell structure formed in the areas near the crack sides, and (2) dislocation tangles of extremely high density developed around the crack tips, where the cell structure is indistinguishable. In the present study, many cracks were observed crossing cells, but few propagated along cell-boundaries. Neither microcracks nor voids were observed ahead of the tips of the cracks inside bulk specimens.
The results obtained here suggest that, as a crack passes, the tangled dislocations ahead of the crack tip disappear or are rearranged to form the boundaries of cells, and, therefore, the propagation of fatigue cracks (Stage II) occurs in a work-hardened area, accompanied by plastic relaxation.
