MECHANISMS OF HYDROGEN-ASSISTED CRACKING

Emphasis is placed on cracking in steels, but fracture of nickel, aluminum and titanium alloys is also considered. Close similarities between hydrogen embrittlement and liquid-metal embrittlement are evident in many cases. These similarities suggest that adsorbed hydrogen is generally responsible. Fractographic evidence suggests that hydrogen-assisted cracking occurs by plastic flow rather than by decohesion at crack tips. The theory that best fits is one that proposes that chemisorption of hydrogen atoms facilitates nucleation of dislocations at crack tips.