SUPERPLASTIC FLOW IN 3 MOL% YTTRIA-STABILISED ZIRCONIA AT HIGH TEMPERATURES

The deformation behaviour of a superplastic 3 mol% yttria stabilised tetragonal zirconia (3Y-TZP) over a wide range of load, strain rates and temperatures (1448-1623 K) under the three modes of loading (bending, compression and tension) was studied. The obtained data were analysed in terms of the following equation: depsilon/dt of the order of sigma n exp(-Q/RT), where depsilon/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, and Q values in the range of 555-587 kJ/mol. There was a good compatibility between the three loading methods. It is shown that flow occurred by Coble diffusion creep, controlled by movement of the Zr4+ ions and, because of the small grain sizes in the material, that creep rates were reduced through interface-controlled diffusion creep. 7 refs.