Silicon nitride flexural strength

Flexural strengths as a function of temperature for silicon nitride composites.24... 

In addition to the initial work in the alumina and mullite matrix systems previously mentioned, SiC whiskers have also been used to reinforce other ceramic matrices such as silicon nitride,9-13 glass,14 15 magnesia-alumina spinel,16 cordierite,17 zirconia,18 alumina/zirconia,18 19 mullite/zirconia,18-21 and boron carbide.22 A summary of the effect of SiC whisker additions on the mechanical properties of various ceramics is given in Table 2.1. As shown, the addition of whiskers increases the fracture toughness of the ceramics in all cases as compared to the same monolithic materials. In many instances, improvements in the flexural strengths were also observed. Also important is the fact that these improvements over the monolithic materials are retained at elevated temperatures in many cases. 

Fig. 2.5 High temperature flexural strength of sialon (Si4 5Al15015N65-2%3Y203-5AI203) and silicon nitride (Si3N4-6% Y203-2% A1203) materials with and without SiC whiskers. Whiskers are from American Matrix.

Fig. 2.6 High temperature flexural strength of silicon nitride (Si3N4-6% Y2Oj-2%A12C>3) materials with various types of SiC whiskers. Whisker content was 20 vol.% for all composites. ACMC is Advanced Composites Materials Corp.

Silicon nitride ceramics should have high flexural strength and fracture toughness at room temperature and good creep resistance at elevated temperatures. Because these properties are determined by the microstructure of these ceramics, further improvement of these ceramics is possible through alloy design. The following sections will be devoted to micro-... 

Lai and Tien [26] (Fig. 15) have shown that the flexure strength and fracture toughness of silicon nitride ceramics depends on the aspect ratio... 

Fig. 21. Flexural strength of RBSN infiltrated with equilibrium liquid. The liquid has the eutectic composition on the Si3N4-Y2Si207 join saturated with silicon nitride crystals [33].

Fig. 1. Specific yield strength (0.2 % proof stress in compression per unit weight density at 10 4s 1 strain rate in compression) as a function of temperature for the D022 phase Al3Nb [112, 113], the Heusler-type phase Co2TiAl [67], the Laves phasesTiCr15Si05 andTaFcAl [67,114], the two-phase alloy NbNiAl-NiAl with 15 vol.% NiAl in the Laves phase NbNiAl [67,114], and the hexagonal D8g phase Ti5Si3 [100] in comparison to the superalloy MA 6000 (in tension) [115] and the hot-pressed silicon nitride HPSN (upper limit of flexural strength) [116],...

Yao DX, Zeng YP (2011) High flexural strength porous silicon nitride prepared via nitridation of silicon powder. J Inorg Mater 26 422-426... 

TABLE 4. Grain size distributions for the Si3N4-BAS composite from different ratio of starting silicon nitride powders with their indentation fracture toughness and flexural strength... 

The ceramic materials investigated in this paper are hot-pressed silicon nitride (HPSN), reaction-bonded silicon nitride (RBSN), zirconia-toughened alumina (AI2O3), and porous SiC. The available material properties for these ceramics are given in Table 4.3. The HPSN and zirconia-toughened alumina ceramics were in the shape of flexural strength test bars cut from billets. The RBSN ceramic was molded into bars of the shape of flexural test specimens. The porous SiC ceramic was provided in the shape of flexural test specimens. 

Bandyopadhyay, B.P. and Ohmori, H., "The Effect of ELID Grinding on the Flexural Strength of Silicon Nitride," to be published in the International Journal of Machine Tools and Manufacture, Pergamon press. 

Addition of SiC particulates to a silicon nitride matrix is expected to improve the mechanical properties of silicon nitride. The flexural strength at 1400° C is considerably improved with the addition of 3 xm SiC particles to a silicon nitride matrix using MgO as a sintering aid [60]. 

Figure 13.5 Flexural strength of silicon nitride vs. temperature.

Density is 1.9 to 2.3 kg/1 and flexural strength 30 to 90 mPa. Silicon oxynitride is used as a lining for cells for the electrolysis of AICI3 to A1 and ZnCl2 to Zn, and as crucibles and tubes for molten salts. It occurs as a constituent of nitride bonds (see silicon nitride, SILICON carbide) and has been used to strengthen silica optical fibres by surface coating. 

Figure 11.16 Flexural strengths of reaction-bonded silicon nitride (RBSN) and dense sintered silicon nitride as a function of temperature. The strong deterioration of the strength of HT superalloys with temperature is given for comparison.

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