Zirconia 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. 

It has been known for some time that considerable improvement of the mechanical properties of alumina in terms of flexural strength, fracture toughness, yield strength and elastic modulus can be achieved by adding particles of stabilised zir-conia as a structural reinforcement (see Chapter 4.1.2). Such ceramics are known as ZTA (zirconia-toughened alumina), duplex ceramics or dispersion ceramics. 

There is a slight decrease in flexural strength and toughness of zirconia ceramics exposed to bodily fluids. The reason is associ-... 

S. R. Choi and N. P. Bansal, High-temperature flexure strength, fracture toughness, and fatigue of zirconia/alumina composites, Ceram. Eng. Sci. Proc., 24 [3] 273-279 (2003). 

The ceramic materials investigated in this paper are hot-pressed silicon nitride (HPSN), reaction-bonded silicon nitride (RBSN), zirconia-toughened alumina (AI2O3), and porous SiC. The available material properties for these ceramics are given in Table 4.3. The HPSN and zirconia-toughened alumina ceramics were in the shape of flexural strength test bars cut from billets. The RBSN ceramic was molded into bars of the shape of flexural test specimens. The porous SiC ceramic was provided in the shape of flexural test specimens. 

Flexural strength versus depth of material removed by lapping results for zirconia-toughened alumina ceramic are shown in Figure 4.11a through... 

Fig. 2.76 Temperature dependence of flexural strength of partially and fully stabilized zirconia single crystals, polycrystalline PSZ, and hot-pressed Si3N4 (HPSN). PSZ is partially stabilized Zr02 with Y2O3 [24], With kind permission of Wiley and Sons...

Fig. 5.48 Flexural strength of composites as a function of total zirconia content [31], With kind permission of Elsevier...

Rieth, P. H., Reed, J. S., and Naumann, A. W. (1976). Fabrication and flexural strength of ultrafine-grained yttria-stabilized zirconia. Am. Ceram. Soc. Bull. 33 717-721, 727. 

A time goes on, more specifications like this may be crafted, possibly for biological materials such as surgical implants. Several ASTM standards for alumina and zirconia materials for surgical implants are on the books, but only require flexural strength, elastic modulus, and hardness at the moment. 

Researchers at NGK Spark Plug developed an LTCC system for MCMs directed toward the personal computer market. Their material, with dielectric constant of 7.0, had sufficient strength to be brazed to Kovar and AUoy 42, a nickel-iron alloy similar to Kovar. The dielectric is a mixture of alumina, CaO, BjOj, and a small amount of zirconia. Varying the alumina content affected the flexural strength and CTE. Flexural strength maximized at 4.0 weight percent alumina. CTE was varied from 4.5 to 6.5, as alumina content varied from 2.0 to 5.0. 

J. Adams, Young s modulus, flexural strength, and fracture of yttria-stabilized zirconia versus temperature. J. Am. Ceram. Soc. 80(4), 903-908 (2000)... 

---