The growing process of a hydrogen blister in a wheel steel was observed in situ with an optical microscope, and the fracture surfaces formed from broken blisters on a wheel steel and bulk metallic glass were investigated. The initiating, growing, cracking and breaking of hydrogen blis-ters are as follows. Supersaturated vacancies can increase greatly during charging and gather together into a vacancy cluster (small cavity). Hydrogen atoms become hydrogen molecules in the vacancy cluster and hydrogen molecules can stabilize the vacancy cluster. The small cavity becomes the nucleus of hydrogen blister. The blister will grow with enter-ing of vacancies and hydrogen atoms. With increasing hy-drogen pressure, plastic deformation occurs first, the hydro-gen blister near the surface extrudes, and then cracks initiate along the wall of the blister with further increasing hydrogen pressure. A cracked blister can grow further through propa-gating of cracks until it breaks.
The nucleating, growing and cracking of hydrogen blister have been investigated experimentally and theoretically. The results show that atomic hydrogen induces superabundant vacancies in metals. The superabundant vacancies and hydrogen aggregate into a hydrogen-vacancy cluster (microcavity). The hydrogen atoms in the microcavity become hydrogen molecules which can stabilize the cluster. And the hydrogen blister nucleates. With the entry of vacancies and hydrogen atoms, the blister nucleus grows and the pressure in the cavity increases. When the stress induced by hydrogen pressure on the blister is up to the cohesive strength, cracks will initiate from the wall of the blister.
REN XueChong ZHOU QingJun CHU WuYang LI JinXu SU YanJing QIAO LiJie
