Supersaturated α-iron in vapour-deposited Fe–C thin films

While the conventional Fe–C phase diagram predicts negligible solubility of carbon in α-Fe at room temperature, there are many examples where substantial carbon supersaturations have been reported. Non-equilibrium processing routes, such as physical vapour deposition (PVD), appear to be particularly well suited to generating very high levels of supersaturation. Few descriptions of the stability and microstructure of the supersaturated state exist, however. In this study, experiments have been performed using two PVD techniques allowing for the production of nanocrystalline films containing between 11 and 16 at% C. Transmission electron microscopy and electron energy loss spectroscopy reveal no phase other than a nearly body-centred cubic iron in the as-deposited films. This result is discussed with respect to the kinetics of carbon rearrangement and the possibility of the stabilization of the supersaturated state via defects.