Project Details
Projekt
Pressure and field assisted sintering of refractory composites and their influence on the microstructural and electrical properties
Subject Area
Glass, Ceramics and Derived Composites
Materials in Sintering Processes and Generative Manufacturing Processes
Materials in Sintering Processes and Generative Manufacturing Processes
Term
since 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 416817512
In the first funding period, the compaction behavior of Al2O3-Nb-(Ta) powder mixtures of different composition and grain size was investigated in a first step. With the help of pressure and field-assisted compaction, it was possible to completely compact almost all Ta and Nb-containing powder mixtures in combination with fine Al2O3. In contrast, the powder mixtures with coarse-grained Al2O3 showed a strong dependence on the material composition during compaction. Another focus of the work was the investigation of the electrical properties, in particular the determination of the percolation number and the development of the electrical conductivity with increasing metal content. Percolation numbers in the range of 7.5-17.5% by volume were determined, with the percolation number for compositions with coarse-grained Al2O3 being lower than with fine-grained Al2O3. Within the 2nd funding period, the structural causes are to be clarified which lead to the composite materials becoming electrically conductive even with low metal content. This should be done with the help of micro-computed tomography (µ-CT), which, in contrast to conventional CT methods, provides a high resolution down to the µm range. Sintered samples with targeted variations in density and composition are examined in µ-CT with regard to the spatial arrangement of the metal particles and their texture with the aim of identifying conductive paths. At the same time, the electrical conductivity of these samples is analyzed as a function of density; the data on the dependence of the conductivity on the Nb or Ta content are already available. The results obtained can be used to correlate the metal content, texture effects and bond density with the electrical conductivities, and percolation numbers can be explained or, if necessary, also predicted. Furthermore, larger quantities of dense Nb-Al2O3 samples are to be produced in the FAST in the 2nd funding period, which are then made available to TP1 in order to produce coarse grains from them. The coarse grains produced in this way should then be compacted again. The samples produced using the two-stage process are then delivered to TP1 in order to examine the wetting behavior of these composites with molten steel, for example. In TP1 it is also planned to produce alginate-generated (coarse) grains with a reduced metal content of 30% by volume Nb or Ta and 70% by volume Al2O3 with an outer layer of pure refractory metal. The sintering behavior of these alginate-generated (coarse) grain sizes is to be analyzed in TP6 using pressure-assisted sintering processes; in addition, the electrical conductivity of the compacted samples is examined.
DFG Programme
Research Units
