Fabrication and microstructural stability of spark plasma sintered Al2O3/Er3Al5O12 eutectic

Abstract

Al2O3-Er3Al5O12 (BAG) eutectic was prepared by a arc melting process under Ar atmosphere. Button shaped melts, containing fine sized irregular eutectic structures of 'Chinese script', with interpenetrated Al2O3 and EAG phases and primary BAG, were achieved by rapid cooling. Pulverized fine powders of eutectic were then consolidated by the spark plasma sintering (SPS) technique, applying different cooling rates (10 degrees C, 600 degrees C) and dwell times at 1700 degrees C, under a uniaxial pressure of 15 MPa. Coarsening of both phases was observed over a long dwell time (10 mm) at the maximum sintering temperature. Applying short holding times (2 mm) and slow cooling rates (10 degrees C/min) led to samples retaining their starting microstructures. The measured Vickers hardness was in the range of 14.11-15.86 GPa, and the fracture toughness of the samples was around 2 MPa m(1/2). In addition, the micro-structural stability of the eutectics was investigated at 1500 degrees C in air atmosphere for 5 and 20 h. Samples sintered with a dwell time of 10 min were found to be unstable at high temperatures due to grain coarsening. On the other hand, samples sintered with a dwell time of 2 mm preserved their main microstructural features following-after the heat treatment. The relationship between microstructural and mechanical properties was also discussed