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Study of microstructure evolution during intermediate stage of sintering of advanced ceramic materials
Jemelka, Marek ; Pouchlý, Václav (oponent) ; Maca, Karel (vedoucí práce)
The primary goal of this master’s thesis was the description of the dependence of a critical density (i. e. the density when tubular pores completely turn to isolated closed pores) and average grain size at this density on different heating rates of intermediate stage sintering process. The obtained results are highly important, e. g. for producing of transparent ceramic armors, high-performance cutting tools or dense bone and joint implants, because they provide information for selection of the most suitable sintering approach in order to obtain pre-sintered samples with critical density and minimal average grain size for subsequent capsule-free post-HIP process. It has been found that for all studied oxide materials (alumina, tetragonal zirconia and cubic zirconia) the critical density is not significantly dependent on heating rate in the range of 2°C/min to 200°C/min and the average values of critical densities are 96.3 %, 92.4 % and 93.0 % for alumina, t-zirconia and c-zirconia, respectively. Previous literature results showed that the critical density is also not dependent on the green body microstructure, therefore, we can conclude that the critical density seems to be a material constant depending on the dihedral angle of the material. The sintering trajectories (the dependence of the average grain size on relative density) were evaluated for all three heating rates (2, 10 and 200°C/min followed by 5min dwell time) as well as for so-called long-dwell sintering (5-10 hours at low sintering temperatures). The results did not explore any new approach leading to decrease of the grain size at the critical density, so the widely used conventional presintering (10°C/min, 5 min dwell time) remains the appropriate method to reach the optimal microstructure prior to post-HIP process.
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Study of microstructure evolution during intermediate stage of sintering of advanced ceramic materials
Jemelka, Marek ; Pouchlý, Václav (oponent) ; Maca, Karel (vedoucí práce)
The primary goal of this master’s thesis was the description of the dependence of a critical density (i. e. the density when tubular pores completely turn to isolated closed pores) and average grain size at this density on different heating rates of intermediate stage sintering process. The obtained results are highly important, e. g. for producing of transparent ceramic armors, high-performance cutting tools or dense bone and joint implants, because they provide information for selection of the most suitable sintering approach in order to obtain pre-sintered samples with critical density and minimal average grain size for subsequent capsule-free post-HIP process. It has been found that for all studied oxide materials (alumina, tetragonal zirconia and cubic zirconia) the critical density is not significantly dependent on heating rate in the range of 2°C/min to 200°C/min and the average values of critical densities are 96.3 %, 92.4 % and 93.0 % for alumina, t-zirconia and c-zirconia, respectively. Previous literature results showed that the critical density is also not dependent on the green body microstructure, therefore, we can conclude that the critical density seems to be a material constant depending on the dihedral angle of the material. The sintering trajectories (the dependence of the average grain size on relative density) were evaluated for all three heating rates (2, 10 and 200°C/min followed by 5min dwell time) as well as for so-called long-dwell sintering (5-10 hours at low sintering temperatures). The results did not explore any new approach leading to decrease of the grain size at the critical density, so the widely used conventional presintering (10°C/min, 5 min dwell time) remains the appropriate method to reach the optimal microstructure prior to post-HIP process.
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