The IF steel was cycled at strain amplitude of £`max = 0.3% and the samples were cycled at 3000¡B6000 and 13000 for observation of surface crack, respectively. The microstructure of the surface and interior of IF steel were examined by the SEM under BEI/ECCI mode.
At 3000 cycles, we can find that many persistent slip bands (PSBs) form in grains, but it¡¦s not easy to find cracks. The main microstructures in the interior are dislocation loop patches and dislocation walls. The microstructures at the surface are dislocation cells, and we find the dislocation cells arrange along their prefer orientation in some grains.
At 6000 cycles, there are many cracks on the surface, but the depth of cracks may be less than 10£gm. The mainly microstructures in the interior and on the surface are almost the same as those at 3000 cycles, but very few dislocation cells can be observed in the interior.
When the fatigue cycles increase to 13000 cycles, there are many long cracks on the surface. The microstructure of crack tips are misorientation cells and the size of misorientation cells are less than 2£gm. It means that the length of cracks will develop if the fatigue cycles increase.
As the result of the observation of surface cracks longer than 50 um in samples at 6000 and 13000 cycles, the microstructure of crack tips consists of misorientation cells which imply a propagating crack.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0817110-211703 |
| Date | 17 August 2010 |
| Creators | Ye, Ding-Hao |
| Contributors | Po-We Kao, New-Jin Ho, Liuwen Chang |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0817110-211703 |
| Rights | not_available, Copyright information available at source archive |
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