Fe-29Ni-17Co (Kovar†) is shown to be susceptible to environmental cracking under anodic polarization conditions in NaCl electrolytes. Cracking initiates at crevice corrosion sites in preference to sites of maximum stress intensity. The average crack propagation rate is electrochemically controlled and correlates directly with the crevice corrosion rate. A hydrogen embrittlement (HE) mechanism best describes the phenomenology of crack propagation. The hydrogen is provided at the crack tip by metal hydrolysis in the corrosion crevice. To demonstrate the general susceptibility of this alloy to HE, Fe-29Ni-17Co is shown to be embrittled by cathodic charging in H2SO4 solution.

Subject
Corrosion rate, Sodium chloride, Dissolution, Crack propagation, Corrosion cracking, Stress cracking, Acidity, Crevices, Crevice corrosion, Alloys, Electrochemical potential, Stress corrosion cracking, Electrolytes
National Association of Corrosion Engineers
1988
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