Silicon carbide whiskers properties

E. R. Fuller, Jr., R. F. Krause, Jr., J. Kelly, R. N. Kacker, E. S. Lagergren, P. S. Wang, J. Barta, P. F. Jahn, T. Y. Tien, and L. Wang, Microstructure, Mechanical Properties, and Machining Performance of Silicon Carbide Whisker-Reinforced Alumina, J. Research NIST, in press. 

The bulk analysis of /3-SiC whiskers shows the least variation in chemistry. In some whiskers, the residual metals content can vary, most likely, as a result of additives that used as catalysts during synthesis. These include iron, cobalt, and chromium. Studies by Karasek et al. [56] have shown that the physical properties of silicon carbide whisker-reinforced composites do not correlate to the bulk properties of the whiskers significantly. This lack of significant correlation is mainly due to the fact that the important phase chemistry of the whisker-matrix interface is controlled by the matrix chemistry and the surface chemistry of the whiskers. There seems to be little impact of the diffusion of materials into or out of the bulk whisker material. 

Recent advances further enhance their commercial potential in metal matrix composites such as aluminum, nickel, and copper ceramic matrix composites, such as alumina, zirconia and silicon nitride and glass ceramic matrix composites such as lithium aluminosilicate. Silicon carbide whiskers increase strength, reduce crack propagation, and add structural reliability in ceramic matrix composites. Structural applications include cutting tool inserts, wear parts, and heat engine parts. They increase strength and stiffness of a metal, and support the design of metal matrix composites with thinner cross sections than those of the metal parts they replace, but with equal properties in applications such as turbine blades, boilers and reactors. 

Ueno, K., and Toibana, Y. (1983). Mechanical properties of silicon nitride ceramic composite reinforced with silicon carbide whisker. Yogyo-Kyokai-Shi 91 491-497 (in Japanese). 

Jing Wang, Litong Zhang, Laifei Cheng et al. Preparation and mechanical properties of silicon carbide whisker reinforced silicon carbide mini composites. Journal of Aeronautical Materials, 29(1) 68-71, 2009. 

The superalloys, as well as alloys of aluminum, magnesium, titanium, and copper, are used as matrix materials. The reinforcement may be in the form of particulates, both continuous and discontinuous fibers, and whiskers concentrations normally range between 10 and 60 vol%. Continuous-fiber materials include carbon, silicon carbide, boron, aluminum oxide, and the refractory metals. However, discontinuous reinforcements consist primarily of silicon carbide whiskers, chopped fibers of aluminum oxide and carbon, or particulates of silicon carbide and aluminum oxide. In a sense, the cermets (Section 16.2) fall within this MMC scheme. Table 16.9 presents the properties of several common metal-matrix, continuous and aligned fiber-reinforced composites. 

Zhang, X. H., Xu, L., Han, W. B., Weng, L., Han, J. C. (2009). Microstmcture and properties of silicon carbide whisker reinforced zirconium diboride ultra-high temperature ceramics. Solid State Sciences, 11,156-161. doi 10.1016/j.solidstate-sciences.2008.05.010. 

Whipple s rules, 20 138 Whisker reinforcement, 5 554, 555, 654 performance in ceramic—matrix composites, 5 572-575 physical properties, 5 557t synthesis, 5 642-643 and toughening, 5 622 Whiskers, silicon carbide, 22 533-534 White... 

R. T. Bhatt, The Properties of Silicon Carbide Fiber-Reinforced Silicon Nitride Composites , in Whisker- and Fiber-Toughened Ceramics, eds. R. A. Bradley, D. E. Clark, D. C. Larsen, and J. O. Stiegler, ASM, Materials Park, PA, 1988, p. 199. 

Metal-Ceramic Composites. Metals such as aluminum, titanium, copper and the intermetallic titanium aluminide, which are reinforced with silicon-carbide fibers or whiskers show an appreciable increase in mechanical properties particularly at elevated temperatures. These composites are being considered for advanced aerospace structures.1 1... 

Silicon carbide (SiC) whiskers are extremely anisotropic, short fibrous crystals and grow from SiC particles along the [111] plane through catalysis. At present, SiC whiskers are usually prepared by vapor reaction and solid methods, and the latter is more economical and more suitable for industrial production. Figure 3.1 shows the microstructures of SiC whiskers. Table 3.1 shows the chemical and physical properties of SiC whiskers. 

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. 

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