Mechanical high-temperature properties and damage behaviour of refractory composites

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Coarse-grained refractory composites have a high potential for applications in hybrid construction, such as in heatable heat shields or as plugs for steel casting due to their low shrinkage during sintering, plasticity at high temperatures and electrical conductivity. The aim of subproject 3 is to investigate in the second funding period the mechanical properties and damage behaviour of the composites and model material composites (hybrid heat shields and hybrid plugs) generated within the research group based on coarse-grained Al2O3 as outer shell and coarse-grained metal-ceramic composites (60% Nb or Ta and 40% Al2O3) as electrically heatable core at high temperatures. The high-temperature properties such as compressive strength, creep and stress relaxation behaviour of the individual components of the material composites (i) coarse-grained Al2O3 and the composites (ii) from the slip casting process, (iii) from granules of the alginate route and (iv) from additively manufactured granules, as well as of the hybrid composite are to be researched in the temperature range relevant to the application. In addition, the influence of cyclic cold isostatic pressing (different pressures and pressure pulsations) and subsequent sintering regimes (1600°C, 1700°C) on the mechanical properties and damage behaviour of the composites with different pre-synthesized grains from subproject 1 at temperatures up to 1600°C will be investigated. The same composite granules are used as for the sandwich structures. Of interest is also the comparison of the mechanical properties of the porous composites with the samples sintered in subproject 6 by means of FAST, which have a much lower or negligible porosity. In addition, the focus is on the fracture mechanical properties. Of particular interest is also the damage behaviour at the ceramic/composite interface in the sandwich structure. 4-point bending tests on notched and unnotched specimens will be used to investigate the damage behaviour of the metal-ceramic core and the coarse-grained Al2O3 cladding. In addition to the acoustic emission measurements, a thermographic investigation will also be applied to the sandwich structures to detect the damage development in the ceramic cladding of the sandwich structures during heating and mechanical loading.