Papers by Author: Paulo A.P. Wendhausen

Abstract: This work evaluates the influence of particle morphology in mixture rheology. Range of particle morphology was used, changing in the mixtures the proportion of spherical powders and irregular powders, respectively gas and water atomized powders, in fraction of 0, 25, 50, 75 and 100% in mass. Components were obtained by mixtures with solid loading very close to critical values. Rheological analysis of the mixtures was elaborated in a capillary rheometry. The solids loading maximum was larger in 10% for the mixtures with only gas atomized powder, when compared to the mixture with just water atomized powder. The mixtures between gas and water atomized powders with maximum solid loading present difficulties in obtaining homogeneity and presents high viscosity.

Abstract: In this work, Metal Injection Molding (MIM) process was applied to manufacture Nd-Fe-B magnets, where carbon residues were quantified. In a separated test, controlled additions of carbon were added prior to sintering in the conventional processing of Nd-Fe-B magnets, aiming to simulate the binder residues with more accuracy. The carbon contents in the sintered magnets were related to final magnetic properties such as remanence and coercivity. It was found that the rare-earth content in the alloy influence the threshold where further additions of carbon will degrade coercivity. This study gives directions on developing binder systems and debinding processes, focusing on reaching adequate carbon levels to maximize final magnetic properties.

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: Research on determined alloys produced by metal injection molding has been done for cost reduction purposes through the use of powders with bigger particle size. However, regarding feedstock homogeneity, certain limitations are presented when coarse particles are used. For instance, homogeneity strongly influences rheological behavior of the feedstock and dimensional control of the sintered part. Therefore, the purpose of this work was to evaluate effectiveness of a modified binder system with the addition of a surfactant polymer which makes the feedstock more homogeneous. This study was carried out on a FeNiP alloy currently processed by MIM, where 50%wt of the iron powder was replaced with course powder having a particle size distribution of D90 less than 47 ,m. Effectiveness of binder systems using a Melt Flow Index (MFI) and the behavior of dimensional accuracy at sintered part were analyzed. Results showed more feedstock homogeneity and less dimensional deviation when a surfactant agent was used.

Abstract: Ni-Fe based soft-magnetic alloys, processed via Metal Injection Molding (MIM), were investigated regarding the influence of processing route on final magnetic properties and compared to fully dense cast materials. The process variations included high and low temperature debinding, different sintering routes and the application of hot isostatic pressing (HIP). The different densities resulting from the process variations were related to maximum magnetic permeability. Results have shown that density, in the range between 7,5g/cm³ and 8,0g/cm³, does not have significant influence on the maximum permeability, allowing cost-effective process routes. It was also verified that fullydense cast alloys still exhibits superior properties, with lower coercive fields and higher permeability, but results achieved after HIP process overcame even the values of these commercial grade alloys.

Abstract: The known process as Metal Injection Molding is derived from the conventional powder metallurgy (M/P) being an alternative for production of parts with complex geometry, great dimensional precision and freedom of chemical composition. The present work has the objective to evaluate the processing of the Fe3Si alloy sintering in the vacuum furnace using as raw materials iron powder carbonyl and prealloyed powder Fe45Si with D90<10-m. Properties of microhardness, density, coercivity, magnetic permeability, and chemical composition was evaluated. The obtained results were compared with what is presented in the literature for parts processed by conventional ways and with parts processed by M/P. A density of 7,620 kg/m3, a coercive field (Hc) of 101.14 A/m, a relative maximum permeability of 5,484 and a residual induction of 1.1 T was achieved by MIM. Comparing with conventional processes (where 100% of densification is reached), the MIM process results were worse, however they were better than P/M.

Abstract: The sintering of Sm2Fe17 compound prior to the nitrogenation process is studied as an alternative process to produce dense Sm2Fe17N3 hard magnets with higher maximum energy products (BH)max than conventional polymer bonded magnets. In order to optimize sintering and nitrogenation processes, powders made from alloys, with different compositions, in the as-cast as well in the as-homogenized state were used. It could be shown that the amount of α-Fe, formed in the casting process, was reduced during sintering and that Sm selective loss is restricted to the surface up to a depth of 100 +m. Moreover the density of the sintered samples was not much affected by the initial composition or by the prior homogenization of the alloys. Although the nitrogenation process was successful in producing the Sm2Fe17N3 as proved by the mass gain, magnetic properties measurements and X-Ray diffraction, the hard magnetic properties were much lower than expected, indicating that other variables, which are discussed in the text, must be considered.

Abstract: This paper compares the effect of using different types of iron powders for the preparation of Sm2Fe17 by calciothermic reduction-diffusion (CRD). Three types of iron powder were used: carbonyl, sponge and water atomized. The results show that, when immediately nitrogenated after the CRD process, Sm2Fe17 prepared from sponge and water atomized iron powders yield Sm2Fe17N3-magnets with a high degree of texture. However, after a suitable treatment with hydrogen followed by nitrogenation, Sm2Fe17-powders made from Carbonyl iron produce magnets with the best quality regarding coercivity, remanence and degree of texture.

Abstract: In order to obtain specific magnetic properties, it is of paramount importance to increase the alloy density of components fabricated by powder metallurgy. An alternative to increase the density of alloys such as Fe-49Co-2V would be the use of elemental Fe and Co instead of the prealloyed powder. Trying to give some insight on the industrial application of this strategy, this paper investigates the replacement of more conventional pre-alloyed Fe-49Co-2V powders with elemental Fe and Co. A previous analysis shows that it is possible to achieve higher densities using elemental Fe and Co powders sintered at the same temperature than Fe-49Co-2V. It is also shown that this leads to a noticeable improvement in some important magnetic properties such as permeability and magnetic induction.

Abstract: A new development in MIM aims at the manufacturing of parts out of two materials, the Two Components Injection Molding, which allows the production of parts with different materials in distinct locations, obtaining different properties in distinct regions of the part. In this work an austenitic stainless steel was combined with tool steel, based on the Two Components Injection Molding process, using dilatometric experiments to analyze the behaviour of materials during sintering. Metallographic analyses and tensile tests were made to verify the microstructure and the strength in the contact area of the two materials.