Micro-mechanical testing of afvanced ceramics: tools, procedures and first results

Abstract

Micro-mechanical testing has lately become a more accessible tool for understanding deformation, strengthening and failure mechanisms at small scales. It has been found that the often considered intrinsic or “intensive” properties of materials, i.e. not size dependent, start to exhibit an extrinsic behaviour if the volume of material tested is reduced down to the level of the micro- or nano-scale. This is true at least for metals, where diverse experimental approaches have shown that the ultimate strength strongly increases in enough small material volumes in the micro-nano range. In ceramics, the small scale testing approach has received much less attention probably because of the absence of dislocation-controlled deformation mechanisms. Even though, it is the only direct method for the study of the mechanical behaviour of ceramics in thin coatings, superficial layers induced by surface degradation processes as in wear, corrosion, etc. Besides, in ceramics with a grain size dependent transformation toughening mechanism, such as zirconia-based ceramics, a clear effect is expected when testing at the micro-scale. In this work the methodology of micro-mechanical testing is presented and is applied to yttria-stabilized zirconia. Advantages and limitations of the technique are discussed and details about the combination of FIB-machining and nanoindentation testing are illustrated. At the same time, first results of the strength in compression of zirconia micropillars are presented and the failure mechanism is discussed.