Pressureless flexural strength

Properties of the pressurelessly-sintered ZrB2-SiC ceramics were shown in Fig 4. It was observed that the flexural strength and elastic modulus almostly had the same trends as the B4C contents changed except for the first two batches. Along with the B4C concentration increased, the elastic modulus decreased sharply at the beginning and then as the B4C inclusion was more than I wt%, the modulus and strength were all hardly dropped. On the other hand, in the first two batches the strength was low and increased as more B4C added. The reasons were not clear at present and... 

Figure 17. Flexural strength of pressureless sintered (=S, unhatched bars) and post-HIPed (=HIPS, hatched bars) S1C-B4C particulate composites [157].

Mechanical properties of SiC-AlN-Y203 composites (SiC 50%wt-AlN 50%wt), pressureless-sintered with an innovative and cost-effective method, were determined before and after oxidation performed at 1300°C for 1 h. As a consequence of the oxidative treatment, fracture toughness increased from 4.6 MPa m to 6.6 MPa m, flexural strength from 420 MPa to 488 MPa, Weibull modulus from 4.5 to 5.3 and thermal shock resistance (expressed as critical temperature difference) from 3I0°C to 380°C. First of all, these results demonstrated that a pre-oxidation treatment is needed to increase the mechanical resistance and reliability of SiC-AlN-Y203 components. Secondarily, the beneficial effects of the oxidation on the mechanical properties could be explained in terms of compressive residual stresses and crack healing ability. 

Table 3. Summary of research results illustrating the effect of temperature on flexural strength of different UHTCs [HP hot pressing, PS pressureless sintering, 4-P 4-point and 3-P 3-pointflexural strength]...

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