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

Abstract

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.

Effects of heating rate on microstructure and property of sintered reaction bonded silicon nitrides

“…40) Suppose the compositions and post-sintering conditions are the same, the lattice oxygen amounts can be roughly evaluated by the ¢ ratio of the nitrided compacts, and the higher value indicates the lower oxygen contents. 28) In this work, the microstructural characteristics were the dominant factor for the thermal conductivity rather than the oxygen contents, and the heating rate of 8 °C/min, which has the higher density and the greater number of the large grains, showed the highest thermal conductivity, as shown in Table 1.…”

“…17) Zhou et al 18) prepared the Si 3 N 4 ceramics with the addition of 2 mol.% Y 2 O 3 and 5 mol.% MgO, which achieved the highest thermal conductivity ever reported of 177 W/(m•K) and better fracture toughness of 11.2 MPa m 1/2 by the SRBSN method. The features of reactant Si particles, 19)23) post-sintering condition, 18),24)27) and nitridation temperature 28) at this composition have been investigated. However, to the best of our knowledge, there have been no studies investigating the effect of heating rate during the nitridation procedure.…”

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

“…This increase was due to the reduction of internal F I G U R E 7 Relation between thermal conductivity and bending strength for Si 3 N 4 sintered by different routes. GPS, 14,28,[40][41][42][43][44][45] gas pressure sintered; SRBSN, sintered reaction-bonded silicon nitride 2,16,18,46,47 ; HP, hot pressing [48][49][50] ; SPS, spark plasma sintering 51,52 ; PLS, pressureless sintering 33 ; HPFS, hot-pressing flowing sintering.…”

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

“…[8][9][10][11][12][13] It was found that raising the sintering temperature and prolonging the sintering time was adequate for increasing the thermal conductivity, 8 while the strength decreased because of grain growth. 14 In the previous work, 15 we investigated the nitridation temperature for silicon compact and achieved compatibly high mechanical strength and thermal conductivity, which are generally known to be in a trade-off relationship. This is because the microstructures and characteristics of the sintered body are strongly affected by those of the nitrided one.…”