上: 主裂面上所見的幾個次裂面. 下: 橫切面上的蝕孔.
某機件上的蝕孔.
下: 蝕孔與從它往下發展的疲勞裂縫. Below: a corrosion pit and the fatigue crack developed downward and thru the thickness of the plate.
下: 蝕後. 眾多的平行線是塑性成型加工所產生的滑移線. 塑性加工後未退火消除其晶格的內儲能量(lattice stored energy) 也會提昇點蝕速率.
下: 上方為主破裂面, 箭頭所指為蝕點(應力集中, 引發破裂)
quoted from:
www.materialsengineer.com/ G-Pitting-Corrosion.htm
Pitting Corrosion
Pitting is a localized form of corrosive attack. Pitting corrosion is typified by the formation of holes or pits on the metal surface. Pitting can cause failure due to perforation while the total corrosion, as measured by weight loss, might be rather minimal. The rate of penetration may be 10 to 100 times that by general corrosion.
Pitting may take some time to initiate and develop to an easily viewable size.
Pitting occurs more readily in a stagnant (不通風處較易發生) environment. The aggressiveness of the corrodent will affect the rate of pitting. |
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