Silicon nitride mechanical properties

Creep Resistsince. Studies on creep resistance of particulate reinforced composites seem to indicate that such composites are less creep resistant than are monolithic matrices. Silicon nitride reinforced with 40 vol % TiN has been found to have a higher creep rate and a reduced creep strength compared to that of unreinforced silicon nitride. Further reduction in properties have been observed with an increase in the volume fraction of particles and a decrease in the particle size (20). Similar results have been found for SiC particulate reinforced silicon nitride (64). Poor creep behavior has been attributed to the presence of glassy phases in the composite, and removal of these from the microstmcture may improve the high temperature mechanical properties (64). 

In the sintering of such materials as silicon nitride, a silica-rich liquid phase is formed which remains in the sintered body as an intra-granular glass, but this phase, while leading to consolidation, can also lead to a deterioration in the high-temperature mechanical properties. 

Most structural PMCs consist of a relatively soft matrix, such as a thermosetting plastic of polyester, phenolic, or epoxy, sometimes referred to as resin-matrix composites. Some typical polymers used as matrices in PMCs are listed in Table 1.28. The list of metals used in MMCs is much shorter. Aluminum, magnesium, titanium, and iron- and nickel-based alloys are the most common (see Table 1.29). These metals are typically utilized due to their combination of low density and good mechanical properties. Matrix materials for CMCs generally fall into fonr categories glass ceramics like lithium aluminosilicate oxide ceramics like aluminnm oxide (alnmina) and mullite nitride ceramics such as silicon nitride and carbide ceramics such as silicon carbide. 

The carbides and nitrides are well known for their hardness and strength, and this section will briefly compare a number of these properties with those of the pure metals. Concentration will be placed here on the first row compounds, since these constitute a complete series, and Mo and W, since these are the most commonly studied metals. As will be shown, the physical and mechanical properties of carbides and nitrides resemble those of ceramics not those of metals. Comparisons will be made with boron carbide (B4C), silicon carbide (SiC), aluminium nitride (AIN), silicon nitride (Si3N4), aluminium oxide (A1203), and diamond, as representative ceramic materials. 

NISTCERAM National Institute of Standards and Techology Gas Research Institute, Ceramics Division mechanical, physical, electrical, thermal, corrosive, and oxidation properties for alumina nitride, beryllia, boron nitride, silicon carbide, silicon nitride, and zirconia... 

Silicon nitride is prized for its hardness (9 out of 10 on the Mohr scale), its wear resistance, and its mechanical strength at elevated temperatures. It melts and dissociates into the elements at 1,900 °C, and has a maximum use temperature near 1,800 °C in the absence of oxygen and near 1,500 °C under oxidizing conditions.41 It also has a relatively low density (3.185 g/cm3). Unlike silicon carbide, silicon nitride is an electrical insulator. The bulk material has a relatively good stability to aggressive chemicals. This combination of properties underlies its uses in internal combustion engines and jet engines. 

Parr NL, Martin GF, May ERW (1960) Preparation, Microstructure and Mechanical Properties of Silicon Nitride. In Popper P (ed) Special Ceramics. Heywood, London, p 102... 

Lewis MH (1994) Crystallisation of Grain Boundary Phases in Silicon Nitride and SiAlON Ceramics. In Hoffmann MJ, Petzow G (eds) Tailoring of Mechanical Properties of Si3N4 Ceramics. NATO ASi Ser E 276, Kliiwer Academic Publishers, Dordrecht, p 217... 

Baskaran, S., and Halloran, J.W. (1994), Fibrous monolithic ceramics III, Mechanical properties and oxidation behavior of the silicon carbide/boron nitride system , J. Am. Ceram. Soc., 77(5) 1249-1255. 

Trice, R.W. (1998), The Elevated Temperature Mechanical Properties of Silicon Nitride/Boron Nitride Fibrous Monoliths, PhD Thesis. University of Michigan, Ann Arbor, MI. 

Table 15.1 Values of the thermal shock resistance parameters R, R, R"" for a range of ceramic materials where HPSN is hot pressed silicon nitride and RBSN is reaction bonded silicon nitride (reprinted from Table 11.1 on p 213 of Ceramics Mechanical Properties, Failure Behaviour, Materials Selection by Munz and Fett, 1999, published with permission from Springer-Verlag GmbFI)...

Bhatt, R.T., Phillips, R.E. (1990), Thermal effects on the mechanical properties of SiC fibre reinforced reaction-bonded silicon nitride matrix composites , J. Mater. Sci., 25, 3401-3407. 

Sialon is the generic name for the large family of silicon nitride solid solutions containing the basic elements Si, Al, O and N. Over the last three decades, the matrix sialon phases (a-, P-, and 0-) have been developed and various excellent reviews are available (Cao and Metselaar, 1991 Ekstrom and Nygren, 1992 Izhevskiy et al., 2000). In the sialon family, a- and P-sialons offer most interest as engineering ceramics because of their excellent combination of mechanical and high-temperature properties. 

Wotting, G., Kanka, B. and Ziegler, G., (1986), Microstructural development, microstructural characterization and relations to mechanical properties of dense silicon nitride , in Hampshire S, Non-oxide Technical and Engineering Ceramics, London and New York, Elsevier Science, 83-96. 

In addition to dense monolithic ceramics, porous silicon nitrides are gaining more importance in technological applications [24], Some porous silicon nitrides with high specific surface area have already been applied as catalysis supports, hot gas filters and biomaterials [25], There is an emerging tendency to facilitate silicon nitride as biomaterial, because of specific mechanical properties that are important for medical applications [25], Moreover, in a recent study it was shown that silicon nitride is a non-toxic, biocompatible ceramic which has the ability to propagate human bone cells in vitro [25], Bioglass and silicon nitride composites have already been realized to combine... 

Concerning carbon nanotube-reinforced silicon nitride matrices, only a few reports have so far been published [19]. In this case, hot isostatic pressing has been used for composite processing. The carbon nanotubes remained in the microstructure only under low pressures (2 MPa) they connect the silicon nitride grains and produce a 15-37% improvement of the mechanical properties as compared with other carbon-filled samples (Fig. 19.11). Increase of pressure... 

Poorteman, M., Descamps, P., Cambier, F., Plisnier, M., Canonne, V., Descamps, J.C., Silicon nitride/silicon carbide nanocomposite obtained by nitridation of SiC fabrication and high temperature mechanical properties, J. Eur. Ceram. Soc., 23, 2003, 2361-2366. 

Becher, P.F. et al. (1994), Microstructural contribution to the fracture resistance of silicon nitride ceramics , in Hoffmann M. J. and Petzow G., Tailoring of Mechanical Properties of Si3N4 Ceramics, NATO ASI Series, Series E Applied Science, 276, Dordrecht, Kluwer Academic, 87-100. 

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