Processing, structure and properties of alumina-YAG eutectic composites

Research over the past 15 years on alumina-YAG eutectic composites as a high temperature structural material is reviewed. It is suggested that this is among the most attractive oxidation-resistant systems for ultra high temperature (1500 degreesC) structural use. Processing methods studied to date result in alumina-YAG composites of varying length scales of constituent phases ranging from micrometers down to nanometers. Variations in constituent geometry from bulk eutectics to fibers and powders have been explored. The microstructures have ranged from single crystal eutectics with both coarse and fine eutectic structures to polycrystalline eutectics. The properties of interest are strength at temperature, creep resistance, fracture toughness and environmental stability. High temperature strength has been found promising and the creep resistance is among the best in oxide ceramics and is sufficient for applications up to 1500 degreesC. The mechanisms of creep have been studied extensively. The fracture resistance continues to be less than desired for most structural applications. The effect of dopants on the fracture behavior has shown some promise, but there has not been a systematic study and is suggested for future work. This system has excellent environmental stability in a combustion environment compared to other high temperature structural solids.