Thermoplastische Formgebung endgestalttreu reaktionsbindender Oxidkeramiken
The aim of this thesis, which was carried out at Forschungszentrum Karlsruhe in the Institute for Materials Research III, was to prove the application of reaction-bonded oxide ceramics of the ternary system Al 2 O 3 -SiO 2 -ZrO 2 for low-pressure injection moulding. These ceramics are based on the intermetallic compounds ZrAl 3 , Zr 2 Si and ZrSi 2 . Because of their comparatively high increase in volume due to oxidation, they allow a complete compensation of sintering shrinkage. Calculations
... age. Calculations revealed that powder contents of 47-71 vol.% are required to achieve zero shrinkage. However, any addition of metal oxides increases the required powder content. Besides the binder and the dispersant, the powder content is of high importance for the rheology of a feedstock for low-pressure injection moulding. Furthermore the particle size, the particle size distribution and the morphology of the particles are playing a decisive role. Different feedstocks based on ZrAl 3 and ZrSi 2 were prepared by variation of the composition, the morphology and the surface character of the powders. The rheological behaviour was investigated. Correlations between rheology and mechanical properties of the produced ceramic samples were identified. The influence of the rheology and the shaping method were assesed by comparing the accuracy of sintered microparts. It was proven, that low-pressure injection moulding of the reaction-bonded oxide ceramics enables net-shape fabrication of ceramic microparts in a very efficient and accurate way under complete compensation of sintering shrinkage. The bending strength of low-pressure injection moulded ZrSiO 4 -ceramics are about 300 MPa, proven under biaxial load as well as in the three point bending test. The mechanical properties and the Weibull modulus are significantly affected by the powder content. The powder content has a crucial influence on the rheology and furthermore on the distribution of defects. In addition, there is an obvious influence of the shaping method on the distribution of defects and on the Weibull parameters. Due to the miniaturisation of the test specimens for the three point bending test there is a shift in the ratio of surface-flaws to volume-defects. Miniaturisized specimens show a 40 % higher three point bending strength than macro specimens. However, even higher values had been expected according to Weibull theory without the limiting influence of surface defects.