Nanoindentation characterization of sub-micrometric Y-TZP ceramics

Three Y-TZP zirconia ceramics with different grain size have been characterized by depth-sensing indenta- tions tests with several peak loads. The analysis of the load- ing-unloading curves gave loading exponents lower than the theoretical values of 2 in most of the cases. The unloading ex- ponent indicated that the unloading contact could be well modelled by a paraboloid of revolution, especially for high peak loads. Independently on the mean grain size, the hardness showed no sign of load-dependency in the investigated range. As for the mean grain size dependency, at low peak loads, no statistical difference was observed among the mate- rials as a consequence of the large data dispersions. At high peak loads, the hardness instead followed the Hall-Petch rela- tion: the smaller was the grain, the higher was the hardness. Also the Young's modulus had a small grain size depen- dence. Higher values were in fact associated to finer micro- structures. This was very likely due to a better microstructural arrangement.