Made available in DSpace on 2014-10-09T12:37:19Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:05Z (GMT). No. of bitstreams: 1 02041.pdf: 7973448 bytes, checksum: 293424e15491e6c324cc1d3a2cc034c5 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The formation of zinc ferrite from zinc and iron compounds, which reacted under sintering conditions, has been investigated. A mechanism of ferrite formation controlled by cation diffusion has been suggested and it has been shown that the nature of the reagents affects the note of ferrite formation. The decomposition of zinc ferrite by alkaline earth compounds, which reacted under sintering conditions, has also been studied. Calcium ferrite was found to be more stable than zinc ferrite but, for kinetic reasons a metastable phase of zinc ferrite was formed more readily. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

The effect of ball milling on the compaction and sintering of nanocrystalline FC-0205 powder was studied in this work. As-received micron-sized FC-0205 powder was subjected to High Energy Ball Milling (HEBM) in an argon atmosphere at different milling time of 0, 8, 16, 20 and 24 hours to obtain nanocrystalline structures. Unmilled, 8 and 16 hour milled powder were compacted using uniaxial die compression at a pressure ranging from 274 MPa to 775 MPa to obtain a relative density from 74% to 95%. The steel powder compacts were sintered at temperatures ranging from 400 °C (752 °F) to 1120 °C (2048 °F) in a controlled atmosphere. Microscopy analysis using Optical Microscope (OM), Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) was performed on the milled powder, and on the green and sintered compacts to examine the grain size, morphology and agglomeration.

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Laser Sintering is an Additive Manufacturing technology that uses digital files to construct 3-dimensional parts by depositing and consolidating layers of powdered material. Application of the technology for metal and ceramic powders is common but the focus of this work was on polymer laser sintering. A significant drawback for polymer laser sintering is the limited selection of materials currently available for use compared with more conventional processes such as injection moulding. This constrains the usefulness of the technology for designers and engineers. A primary reason for this is a lack of detailed understanding of the development process for new materials for laser sintering. This PhD investigation examines some of the key attributes and requirements needed for successfully implementing new polymer-based laser sintering materials. A strategic method for characterizing and identifying new polymer materials was created utilizing thermal measurements, practical and analytical methods to quantify sintering rate, and degradation studies. Validation of this work occurred through the successful integration of a new laser sintering material at industrial project partner Burton Snowboards. Thermal degradation as a result of the laser sintering process was studied in detail and resulted in the creation of a proposed new parameter: Stable Sintering Region (SSR). The term acknowledges and defines the region above the melting point that is the minimum requirement for sintering to occur and an upper limit beyond which polymer deterioration impedes on mechanical properties. A quantitative approach to define the SSR was developed and explored with three different laser sintering materials, two of which were flexible elastomers. The ability to specifically interpret laser sintering process parameters from thermal degradation characterization was created and used to explore the effects of high energy input on tensile properties and molecular weight. The results of these tests showed the potential to identify an Optimum Sintering Range based on maximizing mechanical properties through the control of energy input and molecular weight. This thesis makes a significant contribution to the knowledge and understanding of polymer laser sintering, especially in the context of materials development. Novel concepts such as the Stable Sintering Region were developed using a theoretical approach and practical measurements and were also thoroughly explored for verification. Additionally, a new method to use a powder characterization technique to predict the actual machine parameters of a material in the laser sintering process was quantified. This has several implications for testing new materials for laser sintering and efficiently identifying appropriate processing conditions.

Aluminum powder metallurgy (PM) parts have found applications in automotive, aerospace and transportation. Sintered aluminum parts have been developed and compete with traditionally fabricated ingot metallurgy (IM) products for specific applications. To extend the range of application of (PM) alloys which offer the advantage of net and near net shape production, processing parameters and corrosion behaviour of the aluminum alloys need to be improved. In this research, processing parameters and corrosion behaviour of a commercial Al-Mg-Si aluminum alloy (Alumix 321) were investigated. This alloy is the PM equivalent of wrought AA6061. Four sintering temperatures (610 °C, 620 °C, 630 °C, 640 °C) and two pressing pressures (200 MPa, 400 MPa) were used and the optimum pressing and sintering procedure was selected. In addition to different processing routes of aluminum powder metallurgy alloys, a series of electrochemical experiments on both (IM) and (PM) aluminum alloy was performed with the aim of correlating corrosion behaviour with production techniques. As a modification step, post sintering treatments and surface alteration techniques were applied. Hot rolling, hot swaging, repressing, resin impregnation and shot peening were performed and their effect on corrosion behaviour was investigated; their effect on density, hardness, and microstructure was also studied. Hardness after hot swaging and hot rolling increases and near full density was achieved (? 99%), while for resin impregnation and shot peening surface nature and roughness were affected, respectively. Electrochemical techniques such as open circuit potential (OCP), Tafel extrapolation (TE), cyclic polarization (CP) and stair step polarization (SP) were performed on the ingot, wrought, and post sintered alloys immersed in a 3.5 wt% NaCl solution. Electrochemical experiments show that corrosion current decreases as a result of post sintering treatments. The electrochemical experiments also show different corrosion mechanisms that were later confirmed by the metallographic analysis. The corrosion product and corroded surfaces of the alloys were characterized by optical microscopy, scanning microscopy (SEM), energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS), and X-ray diffraction (XRD). Results show that pitting is the main corrosion mechanism of the wrought alloy. However, powder metallurgy alloys show pitting, crevice, and intergranular corrosion. / Effect of processing parameters on corrosion behaviour of Alumix 321 PM alloy

Recent studies indicate B4C nanopowder may provide additional advantages without loss of established properties. In this study, preliminary forms of graphite-coated B4C nanopowders on the order of 20-40 nm with various additives were sintered and analyzed. Methanol washing was performed on the powders to remove most of the B2O3 impurity usually present. XRD analysis of the powders verified the nanograined nature and, to some extent, the amount of amorphous material within the powders. A dilatometer furnace was used to track the dimensional changes during sintering, and densities of sintered samples were compared to green compact densities. The onset of sintering occurred at various temperatures depending on the dopant and its amount, most often occurring at higher temperatures than expected. This was likely due first to volatilization of residual B2O3 and then to the graphite coatings of the powders preventing direct B4C-B4C contact. Double-stage sintering, where sintering is either slowed, arrested or reversed and then re-accelerated, occurred in all but one sample. Samples with sintered densities greater than 93% theoretical density were hot isostatically pressed (HIP) with the expectation that the post-HIP density would be 100% theoretical density. Ultimately, post-HIP densities increased less than 2% compared to sintered densities.

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Made available in DSpace on 2014-10-09T12:32:15Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:39Z (GMT). No. of bitstreams: 1 02531.pdf: 2279289 bytes, checksum: 1edfd4f1c6bed88132ea0c1644f03839 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

This diploma work is focused on exploitation of high-temperature dilatometry in sintering of advanced ceramic materials. Newly developed software is presented in this diploma work. This software is able to calculate activation energy of sintering process via concept of Master Sintering Curve. In the second part of diploma work the software was verified by evaluation of sintering of four different ceramics materials. The following activation energies of sintering were calculated: 990kJ/mol for tetragonal ZrO2 (3mol% Y2O3), 620kJ/mol for cubic ZrO2 (8mol% Y2O3) and 640kJ/mol resp. 720kJ for Al2O3 with two different particle size.