Eutectic Al2O3-Er3Al5O12 ceramic production and characterization

The study is divided into two main parts. The first part considers the production of Al2O3/Er3Al5O12 (EAG) eutectics without any sintering additives. Spherical melts containing fine sized irregular eutectic structure of "Chinese script" with interpenetrated Al2O3 and EAG phases and primary EAG were achieved by rapid cooling. Pulverized fine powders were then consolidated by spark plasma sintering (SPS) technique applying different cooling rates and dwelling times at 1700°C under a uniaxial pressure of 15 MPa. Coarsening of both phases were observed with long dwelling time (10 min) at maximum temperature. Applying short holding times (2 min) following slow cooling rates (10°C/min) led samples to retain their starting microstructures. The measured Vickers hardness was in the range of 14.11-15.86 GPa and the fracture toughness of the samples were around 2 MPa m1/2. Additionally, the microstructural stability of the eutectics was investigated at 1500°C in air for 5 and 20 hours. Samples sintered with a dwell time of 10 min were found to be unstable at high temperatures due to the grain coarsening. On the other hand samples sintered with a dwell time of 2 min in 1700°C preserved their main microstructural features after the heat treatment. The second part discusses the role of the sintering aid, LiF, in processing Al2O3/Er3Al5O12 (EAG) eutectics. LiF was added to some of the powder lots in fractions ranging from 0.25 to 1 wt.%. The addition of LiF to Al2O3/EAG powder at more than 0.25 wt.% leads to the formation of some disadvantages like cracks within the samples. Addition of LiF resulted in decreased sintering temperature of the composites and also affected positively the microstructural stability of the samples during the heat treatment.