Effects of Y 2 O 3 /MgO ratio on mechanical properties and thermal conductivity of silicon nitride ceramics

We prepared sintered reaction‐bonded silicon nitride ceramics by using yttria and magnesia as sintering additives and evaluated the effects of nitrogen pressure (0.1–1.0 MPa) on their microstructure, bending strength, fracture toughness, and thermal conductivity. The ratio of β phase in the nitrided compacts varied with the pressure and increased with increasing it. Since many β grains in the nitrided compacts were formed and interlocked each other with a stable three‐dimensional structure which restricted the shrinkage during the sintering procedure, many pores remained in the sintered body. Under the middle pressure (0.3–0.5 MPa), the grains grew large because the number of formed nuclei was small. On the other hand, under the high pressures (0.8–1.0 MPa), the grains were relatively fine and uniform because of a large number of nuclei. Since the porosity and grain length depended on the nitridation mechanism, which was affected by the nitrogen pressure, the properties largely varied accordingly. The nitridation at 0.1 MPa gave the best properties in this study.

Section: Discussionmentioning

confidence: 82%

“…Such film can be removed via dissolution in eutectic liquid 21 . In the Si 3 N 4 –Y 2 O 3 –SiO 2 –MgO system, the eutectic liquid is formed around 1200°C 29 . This result is reasonable because Si reacts with N 2 around this temperature, as shown in Figure 7A.…”

Section: Discussionmentioning

confidence: 82%

Effects of nitrogen pressure on properties of sintered reaction‐bonded silicon nitride

Nakashima

Zhou

Tanabe

et al. 2023

“…Comparing 1480°C with and without holding, the nitridation ratio and relative density were higher in the case without holding, indicating that the prolonged nitridation treatment, not the nitridation temperature, would be important for the loss of MgO. Shrinkage can occur together with the formation of the liquid phase of Si 3 N 4 –Y 2 O 3 –SiO 2 –MgO system, in which the eutectic point is reported to be around 1200°C, 23 meaning that the liquid phase can present in all the nitridation procedures. Further, the amount of liquid increase and its viscosity decreases at the elevated temperatures, in which the shrinkage can be definitely promoted.…”

Section: Discussionmentioning

confidence: 96%

Effects of nitridation temperature on properties of sintered reaction‐bonded silicon nitride

Nakashima

Zhou

Tanabe

et al. 2022

We prepared sintered reaction-bonded silicon nitride ceramics by using yttria and magnesia as sintering additives and evaluated effects of the nitridation temperature on their microstructure, bending strength, fracture toughness, and thermal conductivity. The effects of the nitridation temperature were large, but different depending on the property. The ratio of β-phase in the nitrided compacts significantly increased with increasing the nitridation temperature, whereas their microstructures had no clear difference. Although the bending strength varied, it maintains a high value of 800 MPa. Fracture toughness was almost constant regardless the temperature. The thermal conductivity improved as the β-phase in the nitrided compact increases. This resulted in a decrease of the lattice oxygen content and increase of the thermal conductivity. Therefore, elevating the nitridation temperature and consequently the β-phase ratio should be a promising strategy for achieving compatibly high strength and high thermal conductivity, which are generally known to be in a trade-off relationship.

“…The reason for this was that the addition of Y 2 O 3 led to a higher phase transition rate 24,27 and promoted anisotropic grain growth. 28,29 During extrusion deformation, more β-Si 3 N 4 nuclei with high aspect ratio were deflected, resulting in a higher degree of texturing. Therefore, the MgY167 sample obtained the highly textured structure.…”

Section: Phase Compositionmentioning

confidence: 99%

Fabrication of silicon nitride with high thermal conductivity and flexural strength by hot‐pressing flowing sintering

Li,

Jiang,

Pan

et al. 2024

The silicon nitride (Si3N4) possessing enhanced thermal conductivity and flexural strength was sintered by a hot‐pressing flowing sintering (HPFS) method. The effects of extrusion deformation and sintering additives on the density, phase, microstructure, and performances of Si3N4 fabricated by HPFS were investigated. As the strain increased from 67% to 167%, the mean grain diameter of Si3N4 with MgSiN2 as an additive increased by 49%, reaching 1.36 ± .6 µm. The addition of MgSiN2–Y2O3 resulted in a significantly stronger degree of texturing and smaller grain diameter in Si3N4, compared to the incorporation of MgSiN2 alone. The thermal conductivity of Si3N4 with added MgSiN2–Y2O3 increased to 109.1 W m−1 K−1 in the flow direction, and the flexural strength reached the maximum value of 1250.8 ± 39 MPa in the hot‐pressing direction. The results showed that the thermal conductivity and flexure strength of Si3N4 were enhanced due to the formation of texture and the reduction of flaws induced by HPFS. Moreover, HPFS method exhibited outstanding controllability over the microstructures and properties of materials.