Title: Powder-based Indirect Selective Laser Sintering of Ceramics (Poeder-basis selectief laser sinteren van keramieken)
Other Titles: Powder-based Indirect Selective Laser Sintering of Ceramics
Authors: Shahzad, Khuram; S0209861;
Issue Date: 8-Jul-2013
Abstract: In this thesis an additive manufacturing (AM) route based on the selective laser sintering (SLS) principle was developed to fabricate ceramic parts. During SLS, 3D parts are built in an additive way, i.e. layer by layer, without using a mold or die. A 3D CAD model of the part is virtually sliced into thin sections and the parts are built by depositing powder layers representing these slices. A laser beam is used as heating source to locally heat and sinter the deposited powder layer according to predetermined geometries. The sequence of powder deposition and laser scanning is repeated until the 3D part is completed. In this work, an indirect SLS approach was adapted using a sacrificial organic polymer binder phase. A ceramic/binder composite powder was used as a starting material.Laser irradiation of the composite powder deposit layer aims to melt the organic phase that binds the ceramic particles into a component layer.The green SLS parts were subsequently debinded and sintered to increasedensity and strength of the final ceramic part.The first challenge was to produce micrometer sized polymer/ceramic composite powder which contains submicrometer ceramic particles. An innovative powder preparation technique, thermally induced phase separation (TIPS), was developed to produce such powder. This is a simple technique which involves thedissolution of polymer in a suitable solvent by heating, followed by precipitation of the polymer induced by cooling of the solution. Compositespherical powder was successfully synthesized using TIPS. The effect ofthe polymer concentration, cooling rate, stirring and ceramic powder content and type on the polymer and polymer-ceramic composite microsphereswas investigated. The morphology of the composite powder was found to be strongly determined by the amount and particle size of the ceramic phase. The ceramic particles were incorporated into the precipitating polymer sphere during TIPS when submicrometer or nanosized ceramic particles are added to the polymer solution. Agglomeration of composite micropsheres was not observed, in contrast to pure polymer particles. The size of the composite microspheres decreased when increasing the concentration of ceramic powder in the solution. Different grades of spherical alumina-polypropylene (PP), alumina-polyamide (PA) and zirconia-PP composite powder were synthesized by TIPS for selective laser sintering (SLS). The morphology, microsphere size and thermal properties of the composite powder were analyzed.The effect of the composition of the composite starting powder and SLS parameters on the formability of green SLS partswas studied. Laser scanning parameters like laser power, laser scan spacing and laser scan speed were varied to find an optimum set of parameters. To fabricate green parts with sufficient strength allowing post SLS processing, a high polymer content of 60 or 70 vol. % was required,depending on the particle size of the ceramic starting powder. Moreover, the applied laser energy density had to be accurately controlled within a narrow range. Using lower or higher laser energy density resulted indelaminated parts or parts that were too fragile to handle.Although thefabrication of 3D green parts was realized using SLS, the density of the parts was poor (36-54 %) which resulted in a low sintered Al2O3 or ZrO2 ceramic density (32-50 %). To increase the density, green parts were subjected to pressure infiltration (PI) and/or warm isostatic pressing (WIPing). The application of PI and WIPing increased the homogeneity and density of the composite parts which resulted in a higher sintered alumina and zirconia part density of ~ 90 % of the theoretical density.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Surface and Interface Engineered Materials
Production Engineering, Machine Design and Automation (PMA) Section

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