Mullite flexural strength

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. 

The flexural strength of a mullite/20 vol.% SiC whisker composite as a function of temperature is presented in Fig. 2.4. As shown, the significant increase in the strength of the composite is retained up to temperatures of at... 

Table 2 Values of fracture toughness (Kk), fracture strength (erf), flexural strength, and microhardness for 3 2 mullite at different temperatures...

FIGURE 8. Room temperature four-point flexural strength of mullite-Zr02-Y203-SiC whisker composites versus SiC whiskercontent. Published with permission of the J. Am. Ceram. Soc. (15)... 

Limited flexural strength measurements were made at 1250°C on all compositions. Samples were tested in four-point bending and vacuum. A comparison of room temperature and high temperature strength data is given in Fig. 10. It is seen that the strengths of mullite... 

FIGURE 10. Comparison of room tempeiatuie and 1250°C flexural strengths for mullite-SiC and mullite-Zr02-SiC whisker composites. 

The thermal shock resistance of mullite-SiC whisker composites and mullite-Zr02-SiC whisker composites was evaluated by Kelly, et al. using samples prepared as described by Ruh andMazdiyasni. Thermal expansion, flexural strength and Young s modulus were... 

Fibers of mullite and/or yttrium altuninum garnet, Y3AI5O12 (YAG) which possess excellent high temperature mechanical properties such as high flexural strength and low... 

---