Fatigue striation formation in an Fe-3%Si alloy - effects of crystallographic orientation and neighbouring grains

In order to know the criterion of fatigue striation formation, fatigue frac ture surfaces and crack paths were investigated in Fe-3%Si single and bicry stals having various crystallographic orientations. On single crystals, str iations were formed when the loading direction was close to a [110] directi on. In this direction, the crack grew perpendicular to the loading directio n. When the loading direction was near a [111] direction and the crack grew along an inclined plane, no striations were observed. Even in this orienta tion, when the crack grew perpendicular by necessity using bicrystals, stri ations were observed. This suggests that striations are not formed on a spe cial crystallographic plane, but are formed when the fatigue crack plane is perpendicular to the loading direction regardless of crystallographic orie ntation.