The influence of a previous deposition treatment on the final amount of alloying elements (Cr and Ni) deposited and diffused into the surface of iron parts sintered in hollow cathode discharge (HCD) was studied. Cylindrical pure iron pressed samples, being a central cathode, were placed concentrically in the interior of an AISI 310 steel machine-made outer cathode, resulting in a 6 mm inter-cathode radial spacing. The study was divided in two steps: a) deposition treatment with the outer cathode acting as target and the iron sample acting as substrate (1123K -850 ºC- and 60 minutes deposition temperature and time, respectively); and b) deposition treatment plus HCD sintering (1423K -1150 ºC- and 60 minutes sintering temperature and time, respectively). The electrical discharge was generated using a pulsed voltage power source. The results indicate the presence of 6.5 at.% Cr and 6.9 at.% Ni on the samples surface. The concentration profiles were mathematically treated to quantify the actual amounts of Cr and Ni deposited on and diffused into the samples, and the integration of the fitted equations yielded the calculated areas of 133 (µm × at.% Cr) and 105 (µm × at.% Ni), respectively.

Samples of unalloyed iron were sintered in the presence of an abnormal glow discharge using a confined anode-cathode configuration. The samples were placed on a holder acting as the discharge anode inside an AISI 1020 steel hollow cathode. Heating of the outer cathode was obtained by the bombardment of ions and energetic neutral particles. As a consequence of the confined geometry, the sample was efficiently heated mainly by radiation from the cathode. In order to evaluate the results of the sintering process by plasma, samples of unalloyed iron were also sintered in a resistive furnace using the same thermal cycle. The porosity, dimension and morphology of the pores were characterized by means of four basic parameters: area fraction, mean diameter, shape factor and elongation factor. The results show that the shape factor depends on the pore size, a characteristic that was not observed for elongation factor. For samples sintered in plasma reactor or conventional furnace, no significant difference in the porosity or in the pores morphology was observed.

Results of polypropylene removal in injected metallic parts by using plasma technology are presented. The samples were injected with 55.18% Vol. of unalloyed iron powder, 23.57% Vol. of paraffin and 21.25% Vol. of polypropylene. The paraffin was previously removed in hexane bath, followed by a treatment in abnormal glow discharge of argon and hydrogen for the removal of the polypropylene. The electric discharge was generated in two configurations: a confined anode-cathode with the samples placed on the anode and a confined grid (anode)-cathode system with the sample placed on a holder at floating potential inside the grid. In the first geometry, electrons bombarded the sample surface, while in the second, they are collected by the grid. The samples were characterized by mass loss measurements and scanning electron microscopy. The results showed that the hydrogen discharge was more efficient for both configurations, which is attributed to the high reactivity of hydrogen atoms produced in the discharge. In addition, when plasma debinding was performed at 400 ºC for 10 min, by using the confined anode-cathode configuration, the polypropylene removal was total, while in the confined grid (anode)-cathode geometry the removal was approximately 32%. The higher polypropylene removing observed in the anode-cathode configuration is attributed to electron bombardment of the surface of the sample.

Samples of unalloyed iron powder were compacted and sintered in an abnormal glow discharge, generated in a gas mixture of 80% Ar + 20% H2 by using a pulsed power source. The samples were placed on a holder, acting as the discharge cathode, and were heated by the bombardment of ions, strongly accelerated in the cathode sheath. Sintering was performed at temperatures of 1173, 1273 and 1373 K for 30 min, varying the voltage applied to the cathode from 400 to 700 V and pressure ranging from 470 to 2650 Pa. It is shown that the kinetic energy of ions striking the sample surface increased approximately three times, when the voltage changed from 400 to 700 V, with a corresponding reduction of surface porosity. The surface sealing is related to the ion bombardment, which produced a high mobility of surface atoms and consequent enhanced diffusion as well as sputtering and condensation on the concave surface, resulting in an activation of surface sintering.

Sintered metallic porous structures have an application as capillary structures in two-phase heat transfer loops. In this work the manufacturing procedure of tubular porous structures for capillary pump application is discussed. The application of porous structures on capillary pumping systems requires porosity higher than 40% and pore size diameter lower than 20 µm. Carbonyl nickel powder with particle diameter between 3 and 7 µm and stainless steel AISI316L powder with particle diameter between 1 and 22 µm were used as raw material. Sintering under hydrogen atmosphere was performed both in a resistive furnace and in a plasma reactor. Temperature and time were the modified parameters to obtain suitable porosity and roundness on the samples. The porosity was measured using the Arquimedes Principle (MPIF-42), the roundness was evaluated using a simplified measurement technique of the sample diameter and the pore size distribution was determined by image analysis techniques. Images obtained by Scanning Electronic Microscopy were employed on the image analysis. The sintering parameters selected to manufacture nickel samples were 700 °C and 30 min resulting in a porosity of about 44%. The sintering parameters selected to manufacture stainless steel samples were 1000 °C and 30 min resulting in a porosity of about 40%.

Electrochemical experiments together with SEM and X-Ray techniques were carried out in order to evaluate the corrosion resistance, to analyze the surface condition and to characterize the nitride layer of the sintered and sintered/plasma-nitrided Fe-1.5% Mo alloy in Mg(NO3)2 0.5mol.L-1 solution (pH 7.0). The sintered/plasma-nitrided samples presented a higher corrosion resistance, indicating that the surface treatment improved the electrochemical properties of the sintered material. In addition, the nitride layer formed at 500 °C showed better corrosion resistance that the layers formed at higher temperatures. This difference can be ascribed to the nitrogen content in the nitride layer, which at 500°C is higher due to the formation of a phase rich in nitrogen (epsilon phase) while at higher temperatures a phase poor in nitrogen (gamma' phase) is formed.