High α-β phase transition and properties of YbF3-added porous Si3N4 ceramics obtained by low temperature pressureless sintering. (January 2019) - Ding, Honghui
Abstract: In this paper, we used YbF3 as a sintering additive to get a high α-β phase transition in porous Si3 N4 ceramics. The mechanism of YbF3 as sintering additives as well as the relationship between microstructure and mechanical properties have been investigated in detail. In addition, we used pressureless sintering to lower the temperature to 1550 °C. YbF3 makes α-Si3 N4 completely transform to β-Si3 N4, whereas only 41.1% β-Si3 N4 could be obtained with Yb2 O3 . This process yielded ceramics with more flexural strength and increased fracture toughness using less energy. In addition, using YbF3 substituted for part Yb2 O3 could promote sintering behaviors of Si3 N4 ceramics at low temperature to increase α-β phase transition rate and improve the properties of silicon nitride ceramics significantly. In particular, when we used YbF3 -Yb2 O3 as additives, we obtained a flexural strength of 269.87 MPa and a fracture toughness of 4.59 MPa·m 1/2 . Highlights: Porous Si3 N4 ceramics were fabricated at this low temperature (1550 °C) by pressureless sintering. Complete phase transition from α-Si3 N4 to β-Si3 N4 occurs among the liquid phase using YbF3 as a single sintering aid. YbF3 produces liquid phase at a low temperature and promotes sintering behaviors to obtain high perfomance Si3 N4 ceramics.