Influence of pressure on the morphology and structure of surfaces sintered in pulsed DC annular hollow cathode discharge

Modification of the morphology and structure of surfaces sintered in pulsed DC annular hollow cathode discharge (AHCD) at high temperature, subjected to continuous sputtering, was investigated for different gas pressures. The studied AHCD cylindrical surfaces concentrically placed each other comprised the surface of a pressed (green) iron powder sample (bcc, α-Fe structure), at the central cathode, and the internal surface of an austenitic stainless steel tubular part (fcc, γ-Fe structure), at the external cathode. In this case, metal atoms sputtered from the central cathode are condensed, clustered and sintered (in solid state) at the external cathode internal surface, and atoms sputtered from the external cathode tend to undergo the same events in the opposite direction. Sintering was performed at 1150 °C, for 60 min, at 1, 3, 6, and 9 Torr (133, 400, 800 and 1200 Pa, respectively). Results show that the pressure is the key parameter to control the modification of the AHCD processed surface characteristics subjected to the sintering treatment. Sputtering is strongly decreased at high pressures (6–9 Torr) keeping the original-surface structural and morphological characteristics of both the cathodes practically unaltered. On the other hand, significant changes on the surface characteristics of both the cathodes were observed for smaller pressures (1–3 Torr). The most important is that the austenite (γ-Fe) phase initially present in the AISI 310 austenitic stainless steel gives place to a deposited growing layer, mainly constituted by Fe atoms, and thus by the ferrite (α-Fe) phase, in the steel cathode internal surface, associated with a morphological modification from an apparently plasma etched (austenitic) to a rough (ferritic) surface, as the pressure is changed from 9 to 1 Torr. [Display omitted] •Surface changes using hollow cathode discharge sintering technique were made.•The influence of pressure in the process was investigated.•The use of 1–3 Torr induces structural changes on the surfaces.