Sintering unalloyed iron in abnormal glow discharge with superficial chromium enrichment

Sintering of unalloyed iron samples was performed in an abnormal glow discharge using a confined anode-cathode configuration. The samples were placed on a holder acting as the discharge anode, inside a hollow cathode. 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. In addition, the bombardment of the surface cathode by energetic particles produces sputtering of atoms, which by diffusion in the gas phase deposit on the sample surface. During sintering the deposited atoms diffuse into the solid sample, resulting in a layer enriched with elements sputtered out from the cathode. Two different cathode materials, no chromium steel and a chromium containing steel, were used in order to evince the influence of chromium element on the sintering process. It was observed that depending on the ion energy bombardment of the stainless steel cathode, more than 10% in weight of chromium was deposited on the sample surface, which resulted in the stabilization of the alpha phase of iron at the treatment temperature. In this condition, as the diffusion coefficient in the α-phase of iron is about 102 times higher than in the γ-phase, the sintering of this enriched phase is activated. A layer about 20 μm thick containing approximately 10 wt% of chromium was obtained after 1.0 h processing time.