Instrumented nanoindentation investigation into the mechanical behavior of ceramics at moderately elevated temperatures

An analysis of indentation hardness data from three ceramic materials, zirconium diboride, silicon carbide, and titanium nitride, is presented to extract the fundamental deformation parameters at 295 to 623 K. The measured activation volume was of the order of 1 x b(3) to 4 x b(3) (b is the Burgers vector). The calculated activation energies were in the range of 0.75 to 1.61 eV and are typical of lattice-controlled dislocation glide mechanism. Using finite difference simulations, it was demonstrated that there is a significant difference between the plastic strain rate and the total strain rate for materials showing substantial elastic deformation (i.e., large hardness/elastic modulus ratio). Therefore, the measured total strain rates must be converted into plastic strain rates, which require a reduction during loading and an increase during the dwell at maximum load. Additionally, importance of quantification of instrumental thermal drift was discussed and use of either short duration indentation tests or high loads was emphasized.