The effect of surface condition on aqueous corrosion and environmental embrittlement of iron aluminides

This research was focused on the effect that surface condition has on the aqueous corrosion properties and environmental embrittlement of iron aluminides. All tests were performed in a mild acid chloride solution [pH=4, 200 ppm Cl^-] that simulates severe atmospheric exposure. Cyclic anodic polarization tests were performed to determine susceptibility of different surface conditions to localized corrosion. These tests indicate that the as-processed and furnace oxide surfaces performed poorly in comparison to the mechanically cleaned and chemically cleaned surfaces. U-bend tests were conducted to see how either a 750°C oxide surface or a mechanically cleaned surface affected hydrogen embrittlement. At E_corr neither surface condition produced cracking in the U-bend specimens. At the hydrogen charging potential of -1500 mV SHE, the FAL-Mo, FA-129, and FA-84 U-bend specimens cracked but only in the mechanically cleaned surface condition. Slow strain-rate tests were conducted to get a quantitative understanding of the effect that surface condition has on hydrogen embrittlement. For all tests (either at E_corr or at -1500 mV SHE) the percent total plastic elongation was greater for the oxide surface specimens than for the mechanically cleaned samples. This in conjunction with the U-bend results indicates that the furnace oxide on the surface of the specimens provides some protection from hydrogen penetration and thereby retards hydrogen embrittlement effects.