Ferrite stabilization induced by molybdenum enrichment in the surface of unalloyed iron sintered in an abnormal glow discharge

Unalloyed iron was sintered using an abnormal glow discharge with confined anode–cathode configuration. This electrode arrangement allows heating the component as well as enriching the surface with atoms from the cathode. In order to sinter unalloyed iron with molybdenum enrichment, the samples were placed on a holder acting as the discharge anode, inside a cylindrical cathode of Mo. The cathode was heated by the bombardment of ions and fast neutrals accelerated in the cathode sheath and as a consequence of the confined geometry the sample was efficiently heated by thermal radiation. On heating, the ion and neutral species bombardment produces sputtering of atoms of the cathode, which by diffusion in the gas phase deposit on the sample surface. During sintering the deposited atoms diffuse into the sample, resulting in a layer enriched with elements sputtered out from the cathode. Mo enrichment was observed on the sample surface (more than 4 wt%), which resulted in stabilization of the Fe a-phase at the treatment temperature. Under these conditions, as the diffusion coefficient in the Fe a-phase is about 102 times higher than in the g-phase, the sintering of this enriched phase is activated