Alumina superplasticity

Ishihara, S., etal., Stereographic analysis of grain boundary sliding in superplastic deformation of alumina-zirconia two phase ceramics , Mater. Trans. JIM, 1999, 40, 1158-65. 

Sato, E., Morioka, H., Kuribayashi, K., and Sundararaman, D., Effect of small amount of alumina doping on superplastic behaviour of tetragonal zirconia , J. Mater. Sci., 1999, 34, 4511-18. 

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

Lartigue-Korinek, S., C. Carry, F. Dupau, and L. Priestier. 1994. Transmission electron microscopy analysis of grain boundary behavior in superplastic doped aluminas. Materials Science Forum 170-172 409—414. ... 

Fig. 5.8 Scanning electron microscopy micrographs of ultrafine grains of superplastic ceramics a 2Y-TZP, b alumina, c silicon nitride, and d 2Y-TZP/alumina at equal volume fraction [3]. With kind permission of John Wiley and Sons...

In Fig. 5.8, the microstructure of alumina is shown, indicating superplastic behavior (early experiments failed to show superplasticity). Plastic deformation to large strains was achieved, but the window for superplastic fabrication is very narrow, because sintering below 1330 °C is quite difficult and requires much experience for successful production. Above this temperature, grain growth is quite fast. Therefore, proper additives are needed to reduce grain growth above this... 

A typical jump test is shown in Fig. 9.44 of flow stress versus strain. The stress temperature is 1450 °C. The slopes of each line in Fig. 9.44b yield for m 0.5, meaning that the stress exponent of the strain rate is 2 this indicates the superplastic behavior of the zirconia-alumina-spinel composite under the test conditions of temperature and strain rate. In order to determine the activation energy, a plot of strain rate versus the inverse absolute temperature must be made (as in Fig. 9.44c). The average activation energy of PS-HEBM-SPS is 945 kJ/mol, which is much higher than that of the composite processed from nanopowder mixtures (622 kJ/mol). This should represent GBS, if the concept of superplasticity is the dominant mechanism of deformation. Table 9.1 summarizes the strain rates and various temperatures of two and/or three specimens. PS-SPS appears in the Table 9.1 as PS-SPS and is listed under column C. For the purpose of comparison, the flow-stress results for nanopowder mixtures are also listed in Table 9.1 and are smaller than those processed from PS powders with/without HEBM. 

X. Zhou, D. M. Hulbert, J. D. Kuntz, R. K. Sadangi, V Shukla, B. H. Kear, and A. K. Mukheijee, Superplasticity of Zirconia-Alumina-Spinel Nanoceramic Composite by Spark Plasma Sintering of Plasma Sprayed Powders, Mater. Sci. Eng., A394,353-359 (2005). 

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