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Abstract: Metals with certain porosity are a new class of materials with extremely low density and a unique combination of excellent mechanical, thermal, electrical, and biocompatible properties. Absorption of impact and shock energy, dust and fluid filtration, construction materials, and most importantly, biocompatible implants are all potential applications for metallic foams. An orthopaedic implant made of metallic foam can provide an open-cell structure that allows for the ingrowth of new bone tissue and the transport of body fluids. Due to its strong biocompatibility and stable fixation between the implant and human bone, titanium foam has recently received much attention as an implant material. Finite element modelling is a suitable method to obtain an efficiently designed implant. Accurate finite element analyses depend on the precision before implementation as well as the functionality of the material properties employed. Since the mechanical performances of titanium foam and solid titanium are different, a constitutive model for porous metal is required. The model of Deshpande and Fleck in the finite element analysis software ABAQUS is used to describe the compressive and flexural deformation properties of titanium foam with 63.5% porosity. The finite element simulation results were compared with the practical mechanical properties obtained by compression testing of the foam. Finally, the material modelling was used to investigate the stress distributions on the dental implant system.
Keywords: finite element analysis, ABAQUS, titanium foam, sintering, dental implant, material modeling, mechanical properties, bending, compressing
Published in DKUM: 25.09.2024; Views: 0; Downloads: 3
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Abstract: Reaction-formed $MnZn$ ferrite was prepared and the decrease in shrinkage after sintering due to the volume expansion accompanying iron oxidation was studied. Green compacts consisting of the milled raw oxides $Fe_2O_3$, $Mn_3O_4$, $ZnO$ and metallic iron powder were sintered at 1350 °C in air. During the first hold at 800 °C, $Fe$ was oxidized to $\alpha-Fe_2O_3$ and $Zn$ ferrite was formed. Above 1300 °C the reaction bonding was completed and $MnZn$ ferrite, exhibiting a relatively low shrinkage, was formed. The chemical reactions involved during reaction bonding were associated with a volume expansion and porosity formation, compensating for the shrinkage on sintering. Intensive milling decreases the porosity after sintering but induces the oxidation of iron, and partially removes the shrinkage compensation caused by the presence of metallic iron.
Keywords: reaction-forming, $MnZn$ ferrite, inorganic technology, ferrite ceramics, reaction bonded ceramics, sintering, iron oxides, iron
Published in DKUM: 25.08.2017; Views: 1182; Downloads: 112
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Abstract: Fe- and steel-based powder metallurgy (P/M) products, such as steel gears, spurs, locking mechanisms, porous filters, sliding bearings and bushes, as well as other machine parts and structural elements, are mainly produced with the so-called conventional sintering technology. It is the most efficient technology for the mass production of small, complex, functional and structural parts. Therefore, it is the most convenient and popular among all of the P/M technologies. The most important end-user of sintered parts is the automotive industry. However, small, complex, sintered parts can also be frequently used in the furniture and household industries, precise mechanics, articles for recreation and sports. A fine, iron-based powder mixture or prealloyed powder is first automatically uniaxial-die compacted (ADC) into the final shape of the product with a mechanical or hydraulic press and then sintered in a protective atmosphere at approximately 1100 °C. The metal powder mixture must have the appropriate engineering properties given by the chemistry and particle morphology, enabling a fast and reliable die-compaction process. The most important are a high tap density, a good powder flowability and a low compressibility. All this gives the green compacts an appropriate final shape with a smooth surface, a relatively high and uniform green density, as well as a green strength without internal flaws and cracks. In the case of very small two-or-more-heights products, for example, spur gears with a low module, it is very difficult to obtain a uniform green density at acceptable compaction pressures. Often small cracks are formed at height crossings and big differences in the green density appear in smaller or thinner regions. In the frame of our investigation we analysed the influence of the selected prealloyed commercial iron powder’s morphology and its technological properties on automatic die compaction, as well as the sintering process in the case of small two-level sintered gear dimensions of 5/40–7/10×7mm with module m = 0.5. The original iron powder was sieved and the finest powder particle fraction (< 45 µm) was compared with the original powder mixture considering ADC and sintering process. It was found that the selection of the finer powder mixture could not contribute to the improvement in the overall ADC process, as well as a better green compact. In the present paper the results of our investigations are presented and the reasons why a finer powder mixture cannot contribute much to an improvement of the conventional sintering process.
Keywords: Fe-based alloy powders, particles, morphology, microstructure, automatic die compaction, sintering
Published in DKUM: 27.03.2017; Views: 1428; Downloads: 363
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