Reaction Sintering and Properties of Silicon Oxynitride Densified by Hot Isostatic Pressing

Abstract

Silicon oxynitride ceramics were reaction sintered and fully densified by hot isostatic pressing in the temperature range 1700°C to 1950°C from an equimolar mixture of silicon nitride and silica powders without additives. Conversion to SizNLO increases steeply from a level around 5% of the crystalline phases at 1700°C to 280% at 1800°C, and increases a few percent further at higher temperatures. a-Si3N4 is the major residual crystalline phase below 1900°C. The hardness level for materials containing 285% Si2Nz0 is approximately 19 GPa, comparable with the hardness of SiJN4 hot isostatically pressed with 2.5 wt% Y z 0 3 , while the fracture toughness level is around 3.1 MPa m"', being approximately 0.8 MPa mi" lower. The three-point bending strength increased with HIP temperature from approximately 300 to 500 MPa. [Key words: silicon oxynitride, sintering, hot isostatic pressing, X-ray diffraction, mechanical properties.]

Fabrication and characterization of polymer-derived Si2N2O-ZrO2 nanocomposite ceramics

“…Modulus of rupture shows a superior performance in comparison to that of fully dense monolithic Si2N20 (HIPed at 1570-1750~ with a pressure of 33 MPa) studied by Billy et al [30] and compared with polysilazane-derived Si2N20 by Sehrer and Riedel [7]; on the other hand, it is comparable with MOR values presented by Larker [16] for Si2N20 HIPed at extremely high temperature and pressure.…”

“…However, K~c values in Table II [30] and Rundgren et al [13]. A clear improvement is evident i n comparison to values of ~3 MPa m ~ presented by Larker [16]. Both hardness and elastic modulus seems to be lower than those presented in other papers [16,[30][31][32].…”

“…Figure 3 Shrinkage of the specimen during hot pressing under isothermal conditions 1500 ~ Figure 4 Scanning electron micrographs of the fracture surface of the hot-pressed ceramic. Tables II and III and will be discussed in comparison with data corresponding to related silicon oxynitride materials [7,13,16,[30][31][32].…”

“…To overcome these problems, oxide additives giving a liquid phase are generallyused to allow the formation of fully dense ceramics at lower temperatures via a liquid-phase sintering process. Indeed, dense Si2N20 has recently been produced either by pressureless sintering [14,15] using large amounts of sintering aids (10 wt % Y203 and 6% A1203) or by glass-encapsulation hot isostatic pressing (HIP) at 1950 ~ [16].…”

Generic principles of crack-healing ceramics

“…9). Compared to the low level of fracture toughness of 1-2 MPa·m 1/2 associated with the porous and amorphous microstructure of the polymer derived ceramic residue [136], formation of dense crystalline oxinitride/nitride surface layers may attain significantly higher toughness ranging from 3(Si 2 N 2 O) to >6 MPa·m 1/2 (Si 3 N 4 ) [137,138]. Moreover, the catalytic fillers dispersed in the Si-O-C may undergo nitridation reaction, as for example, 3CrSi 2 + 11 2 N 2 3CrN + 2Si 3 N 4 ,…”