Plasma post-oxidation process for nitrocarburized layer

In the process of the formation of a nitride/oxide layer, the effects of H2 gas on the oxidation process have been investigated in both a conventional steam process and a plasma oxidation process. In a conventional steam process a single phase of magnetite (Fe3O4) has been obtained below a H2O/H2 volume ratio of ∼1:2 while a single magnetite phase has been obtained below the O2/H2 volume ratio of ∼1:9 in the plasma oxidation process. In addition, a dense magnetite film with sharp interface feature has been obtained from a plasma oxidation process as shown in the SEM image. The plasma oxidation film showed improved anti-corrosion properties in comparison to steam oxide with higher corrosion potential (−0.07 V) and lower corrosion current density (∼3.8×10−7 A/cm2) in the measurement of the polarization curve.