Evaluation of the environmentally assisted cracking of aluminide intermetallic compounds

A series of mechanical and electrochemical experiments were performed on samples of titanium aluminides, Ti3Al(α2) and iron aluminide (D03-Fe3Al). Electrochemical studies of these alloys in NaCl solution showed that Ti3Al is less susceptible to pitting corrosion than Fe3Al. Both materials were susceptible to stress corrosion cracking whenever the applied potential during stressing was greater than the breakdown potential. The mode of cracking was intergranular and most often multiple cracks were observed on the surface of tested samples. At applied potentials less than the breakdown potential susceptibility to localized corrosion decreased sharply and at the open circuit potential these alloys did not show any susceptibility. Hydrogen embrittlement (HE) was studied by cathodically charging samples with hydrogen. Ti3Al was very susceptible to HE and its tensile properties after hydrogen charging dropped sharply, while Fe3Al was less susceptible and no major changes in mechanical properties were observed. Oxidation rate of both materials were low up to 800 °C, but hot corrosion resistance in molten salt was extremely low. Severe localized corrosion was observed when samples were exposed to a molten sodium sulfate salt.