LAYERED MANUFACTURING OF POROUSCERAMIC PARTS FROM CERAMIC POWDERSAND PRECERAMIC POLYMERS

摘要

Solid freeform processing is used to build porous ceramic preforms, which are then infiltratedrnwith molten metal in order to fabricate Metal Matrix Composites (MMC). In this process,rnselective laser processing of a preceramic polymer serves to bind the ceramic grains togetherrnby decomposing the polymer during laser processing. The preforms, fabricated starting from a silicon carbide powder and a polysiloxane, are then infiltrated with aluminium. The resultingrncomposites show promising microstructures. This process entails several key aspects: mixturernof ceramic powder and polymer, energy transfer from laser beam to polymer-powder bed,rnnon-equilibrium chemical decomposition of polymer and microstructure formation. Arnfundamental model of the selective laser processing of preceramic polymer-ceramic powderrnmixtures is developed through careful experiments and this understanding serves to developrnmodels of the laser/powder interaction and non-equilibrium pyrolysis kinetics of a preceramicrnpolymer. In addition to characterizing porous preforms and the infiltration process, thernlaser/matter interactions and the chemical decomposition of the polymer are studied.rnMeasurements of the optical properties of the powder beds are performed; the results are usedrnto characterize laser/matter interactions. The polymer decomposition in conventionalrnpyrolysis has been characterized and the results are compared with the kinetics of the nonequilibrium laser decomposition. These kinetics are characterized by infra-red microscopyrnamong other techniques. The results allow to determine how local heating by the laser affectsrnthe chemical reactions. In this paper, we give an overview of the current results of thisrnresearch.