Under corrosion conditions or with pre-corroded specimens, the fatigue strength always decreases. This is due to the possibility of corrosion fatigue (due to cyclic straining in a corrosive environment), which leads to a reduction in the number of load cycles. Therefore, the metal-physical processes do not play the decisive role here, but rather corrosive processes on the surface, e.g. notches due to corrosion and thus increased stress intensities.

Best regards, Andreas

Even the impurity atoms adsorbed on the sample's surface atoms may reduce (or enhance) its mechanical strength. This is so-called Rebinder effect. Corrosion alters the subsurface layer structure more heavyly, makes it porous and rough thus providing better conditions for stress concentration.

Dear Sumit,

Oxides or sulfides present as an impurity on surface try to decrease the bonding and ultimately mechanical strength is lost. The environment plays a important role in the fatigue of structural materials like steel, aluminum alloys and titanium alloys. As we know, Corrosion Fatigue is caused by crack development under the simultaneous action of corrosion and cyclic load. The usual case involves rapidly fluctuating stresses that may be well below the tensile strength (if below the tensile strength- FS is down). As stress is increased, the number of cycles required to cause fracture decreases. When metals are exposed to the simultaneous actions of corrosive environment and repeated stress, the fatigue behavior becomes quite different from that in air and there is a significant decrease in fatigue strength. Mostly hydrogen embrittlement is started and metal is under degradation.

Hope it work out for you.

Ashish