Superplastic Flow in 3 mol % Yttria-Stabilized Zirconia at High Temperatures

A detailed study was undertaken to characterize the deformation behaviour of a superplastic 3 mol% yttria stabilised tetragonal zirconia (3 Y-TZP) over a wide range of loads, strain rates and temperatures (1448 - 1623 K) under the three modes of loading (bending, compression and tension). The obtained data were analysed in terms of the following equation: d epsilon /dt approx = sigma exp n exp(-Q/RT), where d epsilon /dt is the strain rate, sigma is the flow stress, Q is the activation energy, R is the gas constant, T is the absolute temperature and n is the constant termed the stress exponent. The n values were in the range of 2.5 - 3, but Q values in the range of 555 - 587 kJ/mol. There was a good compatibility among these three, mentioned above, loading methods. It was also proved that flow occurs by Coble diffusion creep controlled by movement of the Zr exp 4+ ions and, because of the small grain sizes in the material, the creep rates were reduced through interface-controlled diffusion creep. The presented results and conclusions were consistent with Owen and Chokshi data and Berbon and Langdon analysis.