Zirconia-toughened alumina

Begand, S., Oberbach, T., and Gliem, W. (2006) Mechanical properties of hip joint heads made of the dispersion ceramic - alumina toughened zirconia. Key Eng. Mater., 309-311, 1257-1260, 1261-1264. 

N. P. Bansal and S. R. Choi, Processing of alumina-toughened zirconia composites, NASA/TM—2003-212451, National Aeronautics and Space Administration, Glenn Research Center, Cleveland, OH (2003). 

Thompson, I., Rawlings, R.D. (1991), Monitoring thermal shock of alumina and zirconia-toughened alumina by acoustic techniques , J. Mater. Sci., 26, 4534-4540. 

Alumina and toughened zirconia ceramics are used in the wire drawing industry as capstans, pulleys, and guides. Improved product quality, longer component service life, and lower manufacturing costs have been attributed to the use of ceramics. For example, ceramic capstans last up to 10 times longer than carbide-coated capstans. 

We can add a second phase to modify the mechanical properties of a ceramic. An example we discussed in Chapter 18 is the toughening of alumina using zirconia. In this application again, the materials should not react (which is why zirconia is used). 

Toughened Alumina. Numerous researchers have reported that the addition of a second phase, a process referred to as toughening, can increase the strength and toughness of alumina. Schwartz discusses the properties of alumina toughened by additions of various forms of zirconia, and by additions of silicon carbide. Saito discusses alumina toughened by addition of titanium carbide, TiC. 

Ceramics as Valves Alumina or silicon carbide is fhe material for valves. Gate valves used in an irrigation ditch are made of metal or concrete. Slide-gate valves in ladles holding molten steel are made of ceramics. Alumina is the material used to make oxygen valves of respirators used in hospitals. Ball-and seat valves, made of WC-Co, transformation-toughened zirconia, or silicon nitride, are used in downhole pumps required for deep oil wells. 

Metal balls in hip implants are replaced by ceramic balls made of alumina, transformation-toughened alumina, or zirconia (Figure 1.10). 

Golf putters have been constructed with ceramic heads. Some drivers contain ceramic inserts and some golf cleats are also made of ceramics. The ceramics used for all these are transformation-toughened zirconia or alumina. Some bowling balls contain a ceramic core. Some race cars are equipped with ceramic valves and composite ceramic brakes. 

Zirconium oxide is fused with alurnina in electric-arc furnaces to make alumina—zirconia abrasive grains for use in grinding wheels, coated-abrasive disks, and belts (104) (see Abrasives). The addition of zirconia improves the shock resistance of brittle alurnina and toughens the abrasive. Most of the baddeleyite imported is used for this appHcation, as is zirconia produced by burning zirconium carbide nitride. 

What exactly takes place here is not yet completely clear. For the transformation of the zirconium crystal in their free state a temperature of appr. 1200 °Cis needed. It will be clear that this temperature will not be reached in the situation of figure 14.8. Apparently we are not only dealing with a transfer of energy here. To end this item, one more technical term ZTA (Zirconia Toughened Alumina), which is aluminium oxide which has been made tougher by adding zirconium. 

As mentioned previously, the main body of research on whisker-reinforced composites was concerned with alumina, mullite, and silicon nitride matrix materials. None the less, selected work examined zirconia, cordierite, and spinel as matrix materials.16-18 The high temperature strength behavior reported for these composites is summarized in Table 2.5. As shown, the zirconia matrix composites exhibited decreases in room temperature strength with the addition of SiC whiskers. However, the retained strength at 1000°C, was significantly improved for the whisker composites over the monolithic. Claussen and co-workers attributed this behavior to loss of transformation toughening at elevated temperatures for the zirconia monolith, whereas the whisker-reinforcement contribution did not decrease at the higher temperature.17,18... 

C Properties of zirconia toughened alumina.. ZTA, depend on the specific microstiucture and the proportions of zirconia and alumina. d To convert MPa to psi, multiply by 145. 

Fig. 15. Scanning electron microscope photomicrograph of multilayer TiB2/Al203 with zirconia toughened alumina (Adapted from DeAngelis and Weiss, 1990).

Low, I.M., Skala, R, Richards, R. and Perera, D.S. (1993). Synthesis and Properties of Novel Mullite-Zirconia-toughened Alumina Composites . J. Mater. Sci. Lett. 12, 1985-1987. 

Pratapa, S. and Low, I.M. (1996). The Effects of Spodumene Addition on Properties of Functionally-graded Aluminium Titanate/Zirconia-toughened Alumina Composites . In Proceedings of the 2nd International Meeting of Pacific Rim Ceramic Societies. 

Gutierrez-Mora, F. et. al.. Influence of internal stresses on superplastic joining of zirconia-toughened alumina, Acta Mater. 50 (2002) 3475-3486. 

---