High-temperature mechanical properties of zirconia/nickel composites

The creep properties of wet-processed 3 mol% yttria-stabilized tetragonal zirconia (YTZP)–nickel cermets have been studied for metal concentrations of 20 and 40 vol.% (below and above, respectively, the percolation threshold). Compressive creep tests were performed at constant load at temperatures ranging from 950 to 1250 °C and under stresses between 5 and 100 MPa. The experimental results have been correlated with microstructural observations by scanning and transmission electron microscopy. Similar values of the stress exponent n and the activation energy for flow Q were found for the two metal contents studied. Both creep parameters decrease when increasing the stress and/or the temperature. This trend is similar to that exhibited by high-purity monolithic YTZP, indicating that the overall creep behavior of the composites is primarily controlled by the matrix phase. The strain rate of 40 vol.% Ni cermet is one order of magnitude higher than that of 20 vol.% Ni cermet. The mechanical properties of the composites is discussed in terms of a creep model for two-phase materials.