THE INFLUENCE OF YTTRIUM IMPLANTATION ON THE OXIDATION OF IMPURE IRON-CONTAINING C AND MN AT 700-DEGREES-C

A study of impurity-yttrium interactions has been performed during iro n oxidation [p(O-2) = 0.04 Pa, T = 700 degrees C]. Yttrium-implanted s pecimens always exhibit better oxidation behavior compared with blank specimens. On pure iron or the Fe 0.054 wt.%C alloy the beneficial eff ect is attributed to Fe2YO4 formation. With the manganese-containing a llays (Fe 0.2 wt.%Mn), the protective effect of yttrium is attributed to YMnO3 formation. The best oxidation behavior is obtained with impla nted Fe0.18 wt.%Mn-0.041 wt.%C alloys due to the formation of an YMnO3 oxide subscale at the scale-alloy interface. Yttrium implantation als o hinders carbon segregation at the oxide-alloy interface. This effect ensures better scale adherence. With the most-impure alloy, yttrium i mplantation also changes the growth process from external cation diffu sion to predominant inward-oxygen diffusion.