Hydrogen crack initiation and propagation in pure iron single crystal

Abstract

The initiation and propagation of hydrogen cracks in a pure iron single crystal have been investigated via notched tensile tests with simultaneous cathodic charging of hydrogen. The notch opening displacement for hydrogen crack growth when the tensile direction was parallel to [001] was much smaller than for [110] tension. Hydrogen cracks under [001] tension propagated in a straight line on the (001) plane from the notch root with only slight plastic deformation, whereas under [110] tension they propagated in a zigzag fashion with significantly larger plastic strain accompanying many slip bands. The slip band formation and the crack arrest patterns on the fracture surfaces indicate that hydrogen cracks were initiated and propagated by dislocation reactions on the slip systems in accordance with calculations for the maximum resolved shear stress distribution around the crack tip. The difference in hydrogen crack propagation between [001] and [110] oriented specimens has been explained by assuming that 〈001〉 Cottrell dislocations are stabilised by a high density of hydrogen atoms transported by dislocations which coalesce with each other.

MST/1866