ENVIRONMENT-ASSISTED CRACKING OF IRON ALUMINIDE IN 3.5-PERCENT NACL SOLUTION

In 3.5% NaCl solution, the environment-assisted cracking behavior of a n iron aluminide alloy was studied. Slow strain rate tests were done a t different electrochemical potentials. A 55% loss in ductility was fo und when tested at anodic potentials, which suggests a material degrad ation by the aqueous environment. Results of the experiments that carr ied out using pre-immersed specimens and notched tensile specimens con firmed this material degradation to be stress corrosion cracking (SCC) . To identify the mechanism, an electrochemical permeation technique w as employed. By measuring the diffusible hydrogen concentration, sensi tivity to hydrogen embrittlement had been assessed at different potent ials. Fracture surfaces were examined under the scanning electron micr oscope (SEM). Fracture mode was found to be mainly transgranular quasi -cleavage, except the ones tested at anodic potentials (that are 0 mV and -100 mV vs SCE) on which intergranular SCC was found near the edge . It is believed that these cracks were initiated from the pits. These results indicate that the environment-assisted cracking is an intergr anular SCC, controlled by anodic dissolution mechanism.