Flexural silicon nitride

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.

Figure 3.40 Calculated phase velocity of flexural plate waves vs ratio of plate thickness, d, to wavelength. A, for silicon nitride. Material is assumed to have the elastic properties of Si3N4 and no residual tension. The mode shapes ate illustrated at the right with a greatly enlarged vertical scale for clarity. Ellipses at left show the retrograde elliptical particle motions of the lowest S3rmmetric and antisymmetric modes for d/A = 0.03. (Reprinted with pemtission. See Ref. (621.)...

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. 

Table 4. Comparison of Flexural Streng ui of PY-6 Ceramics Made from Different Silicon Nitride Powder Lots...

The creep/fatigue studies Involving a high performance silicon nitride were also initiated. In particular, the creep strain associated with both button-head tensile samples and four-point flexure samples was measured as a function of time and stress at 1370 C, In the case of the button-head tensile samples, a direct-contact capacitance extensometer was used to monitor the displacement during constant load tests. The deflection of the specimen midspan in the flexure samples was measured with respect to the Inner load points using a three-probe LVDT extensometer. Additional details of the experimental procedure are given elsewhere. 

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