Potential of Directionally Solidified Eutectic Ceramics for High Temperature Applications

Directionally solidified eutectic (DSE) ceramics add new potentialities to the advantages of sintered ceramics: a higher strength, almost constant, up to temperatures close to the melting point and a better creep resistance. The microstructure of melt-growth composites (MGC) of ceramic oxides consists in three-dimensional and continuous interconnected networks of single-crystal eutectic phases. After solidification of binary eutectics, the eutectic phases are alumina and either a perovskite or garnet phase. In ternary systems, cubic zirconia is added as a third phase. For very high temperature structural applications such as turbine blades in future aeronautical turbines or thermal power generation systems, the investigation is focused on both binary (Al₂O₃-Y₃Al₅O₁₂ (YAG), Al₂O₃-Er₃Al₅O₁₂ (EAG) and Al₂O₃-GdAlO₃ (GAP)) and ternary (Al₂O₃-YAG-ZrO₂, Al₂O₃-EAG-ZrO₂ and Al₂O₃-GAP-ZrO₂) eutectics. Improving the strength and toughness of DSE ceramics being essential for such practical applications, results concerning the mechanical behavior of these eutectics will be reported after a short presentation concerning microstructure and crystallography. This better knowledge of DSE ceramics has led to the development of a specific Bridgman furnace to produce large crystals and investigate possible applications of DSE ceramics to a new generation of very high temperature gas turbines, e.g. hollow non-cooled nozzles, turbine blades or combustor liner panels.