Hydrogen role in stress corrosion cracking process of iron aluminide Fe{sub 3}Al in NaCl solution

Book · Fri Sep 01 04:00:00 EDT 1995

OSTI ID:99534

Chiu, H; Qiao, L; Mao, X ^[1]

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1. Univ. of Calgary, Alberta (Canada). Dept. of Mechanical Engineering

The stress corrosion cracking behavior of Fe3AI based intermetallic alloy in 3.5% NaCl solution was studied. The role of hydrogen in the cracking process was also defined. The susceptibility of the alloy to hydrogen embrittlement was first investigated by performing tensile tests in air environment and mineral oil. It was found that ductility increased with increasing strain rate when tested in air, but stayed at a high value when tested in mineral oil. This behavior indicates that the alloy is sensitive to hydrogen embrittlement in air. In 3.5% NaCl solution, the environmental effect was studied by slow strain rate tests that were done at electrochemical potentials ranging from {minus}1,000 mV to 0 mV vs SCE. When tested at anodic potentials, from {minus}500 mV to 0 mV vs SCE, ductility reduced from 8.7% to 3.9%. When tested in cathodic region, from {minus}500 mV to {minus}1,000 mV, the ductility was between 7.3% to 9.1%. Results of tests done on pre-immersed specimens and notched tensile specimens confirmed this material degradation to be caused by stress corrosion cracking (SCC). To identify the mechanism, an electrochemical permeation technique was employed. By measuring the diffusible hydrogen concentration, sensitivity to hydrogen embrittlement has been assessed at different potentials. Anodic dissolution is believed to be the controlling mechanism of the SCC as the alloy is less sensitive to hydrogen embrittlement at anodic potentials. Fracture surfaces were examined under the scanning electron microscope (SEM). Fracture mode was found to be mainly transgranular quasi-cleavage, except the ones tested at anodic potentials on which intergranular fracture area was found near the edge. This intergranular fracture, which increases with increasing anodic potential, is believed to be the stress corrosion cracking area. Pits which corroded intergranularly are the crack initiation sites.

• OSTI ID: 99534
• Report Number(s): CONF-950304--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
CORROSIVE EFFECTS
CRACK PROPAGATION
DIFFUSION
EXPERIMENTAL DATA
FRACTURE PROPERTIES
IRON BASE ALLOYS
SODIUM CHLORIDES
STRESS CORROSION