Silicon carbide fracture toughness

There are, of course, many more ceramics available than those listed here alumina is available in many densities, silicon carbide in many qualities. As before, the structure-insensitive properties (density, modulus and melting point) depend little on quality -they do not vary by more than 10%. But the structure-sensitive properties (fracture toughness, modulus of rupture and some thermal properties including expansion) are much more variable. For these, it is essential to consult manufacturers data sheets or conduct your own tests. 

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... 

Hoffman, M., Rodel, J., Stemitzke, M. et al., Fracture toughness and subcritical crack growth in alumina/silicon carbide nanocomposites , Fracture Mechanics of Ceramics, 1996, 12 179. 

Collin, K.M., Rowcliffe, D.J. (2001), Influence of thermal conductivity and fracture toughness on the thermal shork resistance of alumina-silicon-carbide-whisker compositer Journal of the American Ceramic Society, 84(6), 1334—1340. 

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. 

In, the central zone, the regular distribution of transverse cracks shows that the induced strain is rather homogeneous. Consequently, many analytical models can be applied in order to determine the intrinsic parameters of the coatings. The critical cracking energy and the mode I fracture toughness of the deposited silicon carbide film were assessed by means of the model presented previously. It should be remembered that it was first established and developed for composite materials based on research by Kelly and subsequently by Hu ", that when the stress normal to the coating reaches a critical value... 

The fracture toughness values of the silicon carbide deposits on steel thus calculated (cf. Table 6) are of the same order of magnitude as the toughness of a sintered silicon carbide (1 to 4 MPa.m On a tantalum substrate, these are lower. These differences are probably due to residual stresses which vary considerably depending on the nature of the underlying substrate. 

Silicon carbide has attracted considerable interest because of its good mechanical and physical properties and chemical inertness. One of the most important applications of SiC is to produce a matrix reinforced by fibres, forming ceramic-matrix composites. These composite materials exhibit much better fracture toughness than monolithic ceramics. Compared with carbon/carbon composites, fibre-reinforced SiC matrix composites possess superior oxidation resistance and mechanical properties. The Si-C-H-Cl system (e.g. methyltrichlorosilane, CH3SiCl3) has been used for SiC deposition because it is easy to produce stoichiometric SiC deposits. 

The extraordinary mechanical, thermal and electrical properties of carbon nanotubes (CNT) have prompted intense research into a wide range of applications in structural materials, electronics, and chemical processing.Attempts have been made to develop advanced engineering materials with improved or novel properties through the incorporation of carbon nanotubes in selected matrices (polymers, metals and ceramics). But the use of carbon nanotubes to reinforce ceramic composites has not been very successful. So far, only modest improvements of properties were reported in CNTs reinforced silicon carbide and silicon nitride matrix composites, while a noticeable increase of the fracture toughness and of electrical conductivity has been achieved in CNTs reinforced alumina matrix composites. ... 

Silicon carbide can be pressureless sintered by a solid stated process with the aid of B and C to near full density at temperatures in excess of 2100 C. However, the lower fracture toughness (3 to 4 Mpa-m ) limit their use in many potential structural applications [1]. 

MICROSTRUCTURE OF LIQUID PHASE SINTERED SILICON CARBIDE CERAMICS WITH HIGH FRACTURE TOUGHNESS ... 

Sung-Gu Lee and Young-Wook Kim, Relationship between Microstructure and Fracture Toughness of Toughened Silicon Carbide Ceramics, / Am. Ceram. Soc., 84, 1347-53 (2001). 

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