Silicon carbide strength ceramics

L. A. Giannuzzi, K. L. Rugg and R. E. Tressler, High temperature strength and creep behavior of Carborundum alpha silicon carbide fibers, Ceram. Trans., 38,655-666 (1993). 

Properties of Dense Silicon Carbide. Properties of the SiC stmctural ceramics are shown in Table 1. These properties are for representative materials. Variations can exist within a given form depending on the manufacturer. Figure 2 shows the flexure strength of the SiC as a function of temperature. Sintered or sinter/HIP SiC is the preferred material for appHcations at temperatures over 1400°C and the Hquid-phase densified materials show best performance at low temperatures. The reaction-bonded form is utilized primarily for its ease of manufacture and not for superior mechanical properties. 

Other ceramic cutting-tool materials include alumina, Si-Al-0-N, alumina-carbide composites and, more recently, a composite of silicon nitride reinforced with silicon carbide whiskers. This last material can be produced by chemical-vapor infiltration (CVI) and has high strength and toughness as shown in Table 18.3.Cl... 

Soluble polysilane polymers can also be used as precursors to silicon carbide. The first such application, using (PhMeSi)n-(Me2Si)m copolymers ("Polysilastyrene"), was to strengthen silicon nitride ceramics. The Si3N4 ceramic body was soaked in polysilane and refired, leading to the formation of silicon carbide whiskers in the pore spaces and a consequent increase in strength. (U)... 

Fracture strength, of vitreous silica, 22 428 Fracture tests, 1 514 Fracture toughness ceramics, 5 619-623 of silicon carbide, 22 528t of vitreous silica, 22 429 Fracture toughness tests, 10 427 Fracture toughness values... 

Considerable recent activity in the area of ceramic processing is aimed toward the formulation of materials with high strengths, comparable to the room temperature strength of metal alloys, at high temperatures (of the order of 2000 K). The impetus comes from the significant gains made in the last 20 years with materials formed from submicron powders of silicon nitride and silicon carbide and the promise of similar improvements in the near future. 

Fig. 2. Processing C/C composites. Graphiie cloth is impregnated wilh lurfuryl alcohol and pyroty/ed three or more times, each time increasing pan density, strength, and modulus. Next, the part is packed with ceramic powder and fired al 1650 C tu form a silicon carbide coaling on the lop two layers of the luniinuie. to prevent oxidation. (LTV Aerospace and Defense)...

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. 

J.A. Robertson, Continuous High Strength Ceramic Fibers by Pyrolysis of Inorganic-Loaded Ray on i Silicon Carbide and Alumina afml-TR-67-409, Contract AF 33 (615>3881, FMC,... 

Baskaran, S., and Halloran, J.W. (1993), Fibrous monolithic ceramics II, Flexural strength and fracture behavior of the silicon carbide/graphite system , J. Am. Ceram. Soc., 76(9) 2217-2224. 

Brennan, JJ. and Prewo, K.M., Silicon carbide reinforced glass-ceramic matrix composites exhibiting high strength and toughness, J. Mat. Sci., 17, 2371-2783 (1982). 

Rendtel, A., Htibner, H., Hermann, M., Schubert, C., Silicon nitride/silicon carbide nanocomposite materials II, Hot strength, creep and oxidation resistance, J. Am. Ceram. Soc., 81(5), 1998, 1109-1120. 

Sand (silicon dioxide) and coke (carbon) are combined to form silicon carbide (SiC), a compound used in high-strength ceramic materials. 

It was also found that the electrical resistivity of ceramics based on silicon carbide, and, more recently, zinc oxide could be made sensitive to the applied field strength. This has allowed the development of components that absorb transient surges in power lines and suppress sparking between relay contacts. The non-linearity in resistivity is now known to arise because of potential barriers between the crystals in the ceramic. 

The use of non-oxide ceramics (e.g., silicon carbide) as supports, which were also expedient by virtue of their greater mechanical strength, suppressed HC1 adsorption on the carrier to negligible levels and thus avoided the difficulties described. 

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