Papers by Author: Aloísio Nelmo Klein

Abstract: First results of a possible alternative route for plasma assisted processing of 410 LHC steel powder compacts are shown in present work. Carburizing treatment was performed simultaneously with the sintering of samples. The main motivation of this study was verifying the possibility to eliminate the manufacturing step of the carburizing thermochemical treatment, which is normally applied in the production of sintered steel parts subjected for extreme wear conditions. Treatment was carried out in pulsed DC abnormal glow discharge, using gas mixture (atmosphere) of 99%(80% Ar + 20% H₂) + 1.0% CH₄, at 1100 °C, during 60 min, and 9 Torr, for two different conditions, termed: a) Sintering-Carburizing at high flow (for 480 sccm); and b) Sintering-Carburizing at low flow (for 120 sccm). Characterization of the treated samples was performed by Optical Microscopy, SEM, XRD, and microhardness measurements. The presence of CH₄ in the plasma atmosphere proved to be viable to carburize the sample surface while the sintering stage was carried out. Despite of this, further studies are required to optimize both the carburizing + sintering effects, aiming to produce non-brittle structures and parts, opening a new R&D field to the plasma sintering of metallic materials.

Abstract: Previous works studied the colloidal processing of nickel-silica and nickel-titania nanocomposites fabricated via slip casting. A rheological approach was used to characterize and optimize a 30 vol.% nickel aqueous suspension with up to 10 vol.% SiO₂ and 5 vol.% TiO₂ nanoparticles. In this work, the effect of mechanical activation of Ni-SiO₂ and Ni-TiO₂ nanocomposites on microstructural and mechanical properties was studied. For this aim Ni-SiO₂ and Ni TiO₂ slip-cast compacts were attrition milled for up to 12 hours. Green bodies of the mechanical-alloyed powders were obtained by cold pressing (300 MPa). Next, those green bodies were annealed at 700°C for 1 h, repressed at 700 MPa and sintered at 900°C for 1 h in flowing Ar/5%H₂ atmosphere. Porous and dense materials were characterized by SEM/FESEM, Archimedes densities and Vickers microhardness measurements. Mechanical alloying produces a remarkable improvement on microstructure homogenization, sintering densification and hardness comparing with slip-cast composites.

Abstract: Binders based on mixtures of polymers and waxes are suitable both for solvent combined with thermal extraction, as well as for pure thermal debinding. The recently developed plasma-assisted debinding and sintering (PADS) process has been targeted, for historical reasons, on a wax-polymer system, appropriated for solvent combined with thermal extraction processes. This paper shows experimental results related to the debinding rate of parts produced by metal powder injection molding using the recently developed Plasma Assisted Debinding process. Influence of temperature and the ratio of cathodic area on the mass loss were studied.

Abstract: this paper describes the PADS process and equipment, which has been developed to produce PIM components. The use of a hybrid system of plasma discharge and Mo heating elements makes debinding and sintering PIM components in the same heating cycle possible. The use of an abnormal discharge between a cathode and anode under low-pressure provides reactive specimens that break the polymeric chains of the binder of the molded parts. By the combination of these features it was possible to use heating rates of 2,0º C/min during the debinding step. The hydrocarbons, resulted from debinding, are pumped out through vacuum pumps, without traps. The clean environment makes possible to sinter the parts in the same cycle, as well as execute a surface treatment during cooling. The results present short process times as 6 hours to Fe2Ni0,6C low alloy steel and 7 hours to 316-L stainless steel. Characteristics as density, carbon content and mechanical properties are similar to traditional PIM process. The reduction of energy and gas consumption and shorter lead-times are economic advantages of PADS system. The clean environment of PADS is also an ecological advantage.