Abstract
The present contribution reports the influence of nitridation and sintering conditions on the densification, microstructure, mechanical and thermal conductivity properties of sintered reaction bonded Si3N4 (SRBSN) mixed with 3.5% Y2O3-1.5% MgO. The nitridation of samples was carried out at 1450 and 1500°C for different time schedules (2.5, 8 and 16h) in order to increase β Si3N4 phase and subsequently sintering was performed at various temperatures (1850, 1900 and 1950°C) for 10h to enhance densification and properties of SRBSN ceramics. It was observed that the density of the samples slightly decreased and β Si3N4 phase significantly increased to 87% with increasing nitridation temperature and time. The density of gas pressure sintered (GPS) samples increased with increasing sintering temperature, almost full density was measured for all the samples at the respective sintering temperature (except those samples which were given nitridation at 1500°C for 16h). The microstructure of SRBSN samples were characterized by bimodal microstructure with equiaxed and rod like elongated grains and average grain size of SRBSN samples varied between 1.62 and 2.43μm and aspect ratio of grains varied from 3.78 to 6.88 with varying the sintering temperature. Depending on the sintering density and microstructure, the SRBSN samples exhibited hardness (16.69 to 19.47GPa), fracture toughness (7.02 to 9.20MPa·m1/2) and thermal conductivity (77.32 to 98.52W/m·K). The coarsening of grain size and aspect ratio negatively affected hardness and fracture toughness, on the contrary the thermal conductivity increased. Among all samples, the SRBSN (which was subjected to nitridation at 1500°C for 16h; GPS at 1950°C for 10h) measured with good combination of hardness: 17.32GPa, fracture toughness: 8.36MPa·m1/2and thermal conductivity: 98.52W/m·K.
Published Version
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