Mechanical boron carbide ceramics

All the above primarily refers to materials containing relatively small amounts of impurities. However, boron carbide ceramics usually contain 7-20% A1 or AI2O3 to increase hardness and 6-13% silicon to improve mechanical characteristics [98]. Aluminum- and silicon-doped materials often exhibit structural nonuniformity. They have areas of pure boron carbide, and silicon- and aluminum-doped areas [107]. 

Table 11.2 Mechanical properties of self-bonded boron carbide ceramics.

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. 

Although few applications have so far been found for ceramic matrix composites, they have shown considerable promise for certain military applications, especially in the manufacture of armor for personnel protection and military vehicles. Historically, monolithic ("pure") ceramics such as aluminum oxide (Al203), boron carbide (B4C), silicon carbide (SiC), tungsten carbide (WC), and titanium diboride (TiB2) have been used as basic components of armor systems. Research has now shown that embedding some type of reinforcement, such as silicon boride (SiBg) or silicon carbide (SiC), can improve the mechanical properties of any of these ceramics. 

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. 

A method was developed for the examination of boron nitride ceramics by automated ultrasonic inspection [57]. A comparison of sliding and abrasive wear mechanisms in ceramics and cemented carbides shows that a-BN ceramics are quite susceptible to indentation fracture [58]. Many more additional applications are reported in Section 4.1.1.10.8, p. 129. 

Baharvandi H. Hadian A Alizadeh A. (2006). Processing and Mechanical Properties of Boron Carbide-titanium Diboride Ceramic Matrix Composites. Applied Composite Materials, Vol. 13, No. 3, May, 2006, pp. 191-198, ISSN0929189X Basu B. Vleugels J. Biest O. (2005). Processing and Mechanical Properties of Zr02-TiB2 Composites. Journal of the European Ceramic Society, Vol. 25, No.l6, May,2005, pp.3629- 3637, ISSN 09552219... 

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... 

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. 

Nonoxide ceramics, such as silicon carbides, silicon nitrides, and boron nitrides, have unique mechanical and functional characteristics. Silicon carbides with high thermal conductivity, high thermal stability, excellent mechanical strength, and chemical inertness are especially considered as effective catalyst supports. 

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