High-temperature mechanical behavior of partially sintered ceramics

The high-temperature mechanical behavior (elastic properties, fracture strength, and degree of irreversible deformation) of partially sintered alumina and zirconia ceramics with different porosities and degrees of sintering was evaluated by (static) three-point bending tests at 1100 °C, from which load–deflection curves were obtained. Furthermore, the elastic modulus obtained from these curves was compared to Young’s modulus as measured via the impulse excitation technique. Bar-shaped specimens were prepared by uniaxial pressing and sintering at 1100, 1200, 1300 and 1400 °C for 2 h, and subsequently characterized via bulk density measurements, total porosity calculations and electron scanning microscopy analysis. The effects caused by progressive sintering and the occurrence of irreversible deformation due to the weak bonds (small sinter necks) between particles affected the values of the static elastic modulus, which resulted in values quite lower than those obtained by the impulse excitation technique. A very good correlation described with a power-law relationship was obtained between both type of modulus, dynamic and static one, in the whole range of sintering temperatures for the two evaluated porous ceramics. In particular, the very fine (nanocrystalline) grain size and the tendency to agglomerate of the zirconia powder facilitated the irreversible deformation by grain boundary sliding.